QCLs are becoming the most important sources of laser radiation in the midwave infrared (MWIR) and longwave infrared (LWIR) regions because of their size, weight, power and reliability advantages over other laser sources in the same spectral regions. The availability of multiwatt RT operation QCLs from 3.5 μm to >16 μm with wall plug efficiency of 10% or higher is hastening the replacement of traditional sources such as OPOs and OPSELs in many applications. QCLs can replace CO₂ lasers in many low power applications. Of the two leading groups in improvements in QCL performance, Pranalytica is the commercial organization that has been supplying the highest performance QCLs to various customers for over four year. Using a new QCL design concept, the non-resonant extraction [1], we have achieved CW/RT power of >4.7 W and WPE of >17% in the 4.4 μm - 5.0 μm region. In the LWIR region, we have recently demonstrated QCLs with CW/RT power exceeding 1 W with WPE of nearly 10 % in the 7.0 μm-10.0 μm region. In general, the high power CW/RT operation requires use of TECs to maintain QCLs at appropriate operating temperatures. However, TECs consume additional electrical power, which is not desirable for handheld, battery-operated applications, where system power conversion efficiency is more important than just the QCL chip level power conversion efficiency. In high duty cycle pulsed (quasi-CW) mode, the QCLs can be operated without TECs and have produced nearly the same average power as that available in CW mode with TECs. Multiwatt average powers are obtained even in ambient T>70°C, with true efficiency of electrical power-to-optical power conversion being above 10%. Because of the availability of QCLs with multiwatt power outputs and wavelength range covering a spectral region from ~3.5 μm to >16 μm, the QCLs have found instantaneous acceptance for insertion into multitude of defense and homeland security applications, including laser sources for infrared countermeasures for protecting aircraft from MANPADS, testing of infrared countermeasures, MWIR and LWIR lasers for identify-friend-or-foe (IFF) personnel beacons, infrared target illuminators and designators and tunable QCL applications including in-situ and standoff detection of chemical warfare agents (CWAs) and explosives. The last of these applications addresses a very important and timely need for detection of improvised explosive devices (IEDs) in combat environments like Iraq and Afghanistan.

Surface-plasmon polaritons (SPPs) are electromagnetic waves which are bound at a metal/dielectric interface. SPPs dispersion relation allows bent propagation and can lead to sub-wavelength energy concentration. These properties, well known in the visible and near-infrared, are lost at mid-infrared and THz wavelengths. Here we demonstrate an integrated device which is able to recover and exploit the confinement properties of SPPs. It operates in the mid-infrared wavelengths by electrical injection, It generates plasmonic excitations whose dispersion is artificially tailored via proper patterning of a purely metallic surface. We illustrate the power of this approach by demonstrating bending, focusing and sub-wavelength energy concentration. We demonstrate a compact (<0.1 mm2) device, which is electrically driven and is able to generate, couple, propagate on a chip over macroscopic distances, and focus mid infrared radiation into a subwavelength region.

For the scattering of an incident plane electromagnetic wave by a slotted metallic film, the previous analytical calculation for a single slot is generalized into a model for an arbitrary linear array of slots with variable slot width, slot separation and slot dielectric material. The advantage as well as the effectiveness of the generalized model presented in this work are best described by enabling calculation of a continuous spatial distribution of an electromagnetic field by inverting a small discrete coefficient matrix spanned by both the slot index and the sloteigenmode index for a set of linear equations. In comparisons with well-known plane-wave and finite-difference time-domain methods, inverting a large matrix, in wave number space for the former case and in real space at each time step for the latter case, can be avoided to greatly speed up numerical calculations. In addition, based on a partial-domain method, the formalism presented here can be employed to treat a composite surface (e.g., a slotted metal film with different dielectric materials in the slots).

Metamaterials exhibiting a negative index of refraction in the visible are of recent interest due to many possible applications including cloaking and perfect lensing. Nanoparticle dispersed metamaterials have been researched due to their flexibility in operating frequency, electronic tunability, ease of fabrication and low cost. We propose sputtered binary polaritronic-plasmonic nanoparticles as candidates for metamaterials. Specifically, we show that co-sputtered SiC and Ag nanoparticles are used to obtain a negative index in the visible. Experimental verification of the negative refractive index include the z-scan technique for measurement of the linear refractive index, phase and group velocity measurements using a double Michelson interferometer, and surface plasmon resonance measurements for s and p polarizations for finding the effective permeability and permittivity. Through numerical simulations, we show that our nanoparticle mixture can yield near-field super-resolution for both TE and TM polarizations.

We will present a brief overview of the interest in subwavelength gratings for spectral filtering in the mid-infrared wavelength range. Guided-mode, plasmonic and dipolar resonances will be considered. We will particularly focus on components fabricated in our laboratories, achieving band-pass or cut-band filtering. Optical characterization will be shown, revealing resonances with high quality factors. Multispectral camera has been realized by integrating our components into a cooled infrared focal plane array.

We fabricated a variety of periodic and random III-V, IV, and II-IV semiconductor nanostructures based on various materials, such as Si, GaAs, ZnO, sapphire, etc., by top-down and bottom-up processes for optoelectronic device applications. The periodic arrays of nanostructures were fabricated by the dry etching after forming nanopatterns using the laser interference lithography or monolayer assembly of silica nanospheres. The random nanostructures were formed by a thermal dewetting process of continuous metal thin films and a subsequent dry etching process. Also, the porous films with nanocolumns were formed by a glancing angle deposition. The ZnO nanostructures were fabricated by the hydrothermal growth and electrochemical deposition. The optical properties of the fabricated nanostructures were measured, together with theoretical analyses using the rigorous coupled-wave analysis method. To improve the device performance, these semiconductor nanostructures were applied to the devices such as light emitting diodes, solar cells, and sensors.

To improve the Mid-Infrared (IR) chemical sensing capabilities in liquids and gases, a polymer based waveguide that has 100% interaction with Quantum Cascade (QC) laser field is proposed and demonstrated. The waveguide has thickness down to 10s nanometers so that chemical diffusion and preconcentration could happen very fast; the path length is increased from several microns to over centimeters due to the high spectral and diffraction brightness of QC lasers. Efficient prism coupling into whispering gallery resonators' coated with submicron polymers and planar slab polymer waveguide are demonstrated, high signal to noise ratio is obtained and potential applications discussed.

The development and performance of a continuous wave (CW), thermoelectrically cooled (TEC) external cavity quantum cascade laser (EC-QCL) based sensor for quantitative measurements of nitric oxide (NO) concentrations in exhaled breath will be reported. Human breath contains ~ 400 different chemical species, usually at ultra low concentration levels, which can serve as biomarkers for the identification and monitoring of human diseases or wellness states. By monitoring exhaled NO concentration levels, a fast non-invasive diagnostic method for treatment of patients with asthma and chronic obstructive pulmonary disease (COPD) is feasible. The NO concentration measurements are performed with a 2f wavelength modulation based quartz enhanced photoacoustic spectroscopy (QEPAS) technique, which is very suitable for real time breath measurements, due to the fast gas exchange inside a compact QEPAS gas cell (<5 mm³ typical volume). In order to target the optimal interference free NO R (6.5) absorption doublet at 1900.08 cm^-1(λ~5.263 μm) a Daylight Solutions Inc. widely tunable, mode-hop free 100 mW EC-QCL was used. The sensor reference channel includes a 10 cm long reference cell, filled with a 0.5% NO in N₂ at 150 Torr, which is used for line-locking purpose. A minimum detection limit (1σ) for the EC-QCL based line locked NO sensor is ~5 ppbv with a 1 sec update time by a custom built control QCL compatible electronics unit.

We report here modified absorption property of InGaAs nano-membrane on a Fano filter made of patterned single crystalline silicon nano-membrane transferred onto glass substrate. Placement of an ultra-thin InGaAs film on Si Fano resonant membrane enhances the absorption with simulated enhancement factor ~35 and measured enhancement factor of ~26. Leaky modes in the photonic crystal (PC) consist of high field standing waves that can be coupled to the out of plane radiation mode provided by lattice matching of the PC. We will present simulation, device fabrication and experimental characterization of stacked ultra-thin InGaAs/Si Fano resonance membrane in the IR regime.

The MOVPE growth properties of GaAsN and InAsN in H₂ and N₂ mixed carrier gases are studied. The N contents of the GaAsN and InAsN films increase with increasing the N₂/(H₂+N₂) ratio in the H₂ and N₂ mixed carrier gas. The growth rate reduction of GaAsN films in higher N₂/(H₂+N₂) ratio is explained by the smaller diffusion coefficients of precursors. The pyrolysis of 1,1-dimethylhydrazine (DMHy) is investigated by a quadrupole mass spectrometer (QMS) that is combined with the MOVPE growth reactor. At lower temperatures, the pyrolysis of DMHy in H₂ carrier gas is higher than that in N₂ carrier gas. The results indicate that the higher N contents at the higher N₂/(H₂+N₂) ratios in the mixed carrier gases are attributed to the suppression of the decomposition of III-V-N films as NHx. The higher reactor pressure also exhibits higher N contents in each carrier gas. It is interpreted as the effect of the faster growth rates and the higher DMHy pyrolysis.

InSb nanostructures embedded in InAs and InAsSb matrices were grown on InAs (001) and GaAs (001) substrates by molecular beam epitaxy. The diameter and height of InSb quantum dots (QDs) on InAs with 2ML-InSb coverage grown by Stranski-Krastanov (S-K) are ~36.8 nm and ~3.1 nm, respectively. The density of QDs is ~2.5×10¹⁰ cm^-2. The size distribution of InSb QDs on InAs with 2ML-InSb coverage grown by migration enhanced epitaxy (MEE) was larger than that of its S-K counterpart. Unique InSb quantum dashes (Q-dashes) on InAsSb elongated along two directions were found on an AlSb-buffered GaAs substrate. InSb Q-dashes grown by migration enhanced epitaxy (MEE) were ~159 nm in length, ~63 nm in width, and ~11 nm in height. A large reduction of volume of InSb structures between those in the matrix and those on the surface was found. Threading disl°Cations resulting from the Q-dash structures were also observed. This may be attributed to As-Sb exchange.

InAs/InAs_1-xSb_x strain-balanced superlattices (SLs) on GaSb are a viable alternative to the well-studied InAs/Ga_1-xIn_xSb SLs for mid- and long-wavelength infrared (MWIR and LWIR) laser and photodetector applications, but the InAs/InAs_1-xSb_x SLs are not as thoroughly investigated. Therefore, the valence band offset between InAs and InAs/InAs_1-xSb_x, a critical parameter necessary to predict the SL bandgap, must be further examined to produce InAs/InAs_1-xSb_x SLs for devices operational at MWIR and LWIR wavelengths. The effective bandgap energies of InAs/InAs_1-xSb_x SLs with x = 0.28 - 0.40 are designed using a three-band envelope function approximation model. Multiple 0.5 μm-thick SL samples are grown by molecular beam epitaxy on GaSb substrates. Structural characterization using x-ray diffraction and atomic force microscopy reveals excellent crystalline properties with SL zero-order peak full-width-half-maximums between 30 and 40 arcsec and 20 x 20 μm2 area root-mean-square roughnesses of 1.6 - 2.7 A. Photoluminescence (PL) spectra of these samples cover 5 to 8 μm, and the band offset between InAs and InAs/InAs_1-xSb_x is obtained by fitting the PL peaks to the calculated values. The bowing in the valence band is found to depend on the initial InAs/InSb valence band offset and changes linearly with x as C_{Ev_bowing} = 1.58x - 0.62 eV when an InAs/InAs_1-xSb_x bandgap bowing parameter of 0.67 eV is assumed. A fractional valence band offset, Q_v = ΔE_v/ΔE_g, of 1.75 ± 0.03 is determined and is practically constant in the composition range studied.

In this paper we describe the design and performance of nonlinear quantum cascade laser sources for near-infrared and terahertz applications. Our devices are based on monolithically integrated mid-infrared quantum cascade lasers and passive nonlinear structures which provide a giant nonlinear response for the pumping frequency. Such design concept can be applied for both short-wavelength and long-wavelength generation. In our work, short-wavelength devices were based on the concept of second-harmonic generation whereas long-wavelength devices utilized difference-frequency generation. With this approach we demonstrate room-temperature operation down to 2.7 μm for near-infrared devices and up to 70 μm at 210 K for terahertz devices. The performance of our nonlinear devices is very sensitive to the resonance condition for the pump and nonlinearity. We demonstrate that, once resonant, nonlinear powers in the mW range are available.

The intrinsic narrow linewidth of quantum cascade lasers (QCLs) promises wide applications such as highsensitive trace-gas detection. However, so far limited work has been reported in intrinsic linewidth characteristics of QCLs. In this paper, we theoretically investigate the linewidth broadening caused by intrinsic temperature fluctuations in both mid-infrared and Terahertz QCLs. When microscopic features of the refractive index variations associated with the intersubband transitions and energy level broadening in mid-infrared QCLs are considered, the linewidth broadening increases up to a few hundred Hz in mid-IR QCLs.

We demonstrate room temperature, continuous wave operation of quantum cascade ring lasers around 5 μm with single mode operation up to 0.51 W output power. Single mode operation persists up to 0.4 W. Light is coupled out of the ring cavity through the substrate with a second order distributed feedback grating. The substrate emission scheme allows for epilayer-down bonding, which leads to room temperature continuous wave operation. The far field analysis indicates that the device operates in a high order mode.

Room temperature III-nitride QCL THz is reported. With increasing carrier concentration, the peak in optical shifts towards higher energies. Peak in the optical gain increases with carrier concentration demonstrating a blue shift correlated to quantum confinement. THz power increases linearly with current demonstrating an output power of 0.4448 μW at 6THz. A higher THz power is obtained in Al_xGa_1-xN/GaN/Al_xGa_1-x heterostructures as compared to heterostructures incorporating In. An increase in the Al-mole fraction results in higher THz power.

In this work, we present a comprehensive study of the photocurrent phenomena in single defect-free GaN nanowires (NWs), analyzing the effect of the contact nature, excitation power, light polarization, measuring frequency, and environment. GaN NWs present high photocurrent gain, in the range of 1E5-1E8, with the photocurrent increasing sublinearly with the excitation power. The spectral response is relatively flat for excitation above the GaN bandgap and presents a visible rejection of more than six orders of magnitude. In depleted nanowires (diameter < 100 nm), the photocurrent time response is in the milisecond range, far from the persistent photoconductivity effects (seconds, minutes) observed in larger NWs or two-dimensional layers. From the above-described results, we confirm that the photoresponse is dominated by the redistribution of charge at the surface levels. However, the total depletion of the NW active region reduces the surface band bending preventing persistent photoconductivity effects and granting insensitivity to the chemical environment.

We report on the self-assembly by Au-catalyzed metalorganic vapor phase epitaxy (MOVPE) of GaAs-based nanowires (NWs) and their applications to novel and efficient nano-devices. The growth of GaAs and GaAs-AlGaAs core-shell NWs is presented as case study, focusing on the dependence of their structural, optical and electrical properties on MOVPE conditions. MSM diodes fabricated using as-grown core-shell NWs are reported, along with their photoelectric performances. These devices show potentials for applications as fast photo-detectors and efficient solar cells.

Quantum dot (QD) functionalized nanowire arrays are attractive structures for low cost high efficiency solar cells. QDs have the potential for higher quantum efficiency, increased stability and lifetime compared to traditional dyes, as well as the potential for multiple electron generation per photon. Nanowire array scaffolds constitute efficient, low resistance electron transport pathways which minimize the hopping mechanism in the charge transport process of quantum dot solar cells. However, the use of liquid electrolytes as a hole transport medium within such scaffold device structures have led to significant degradation of the QDs. In this work, we first present the synthesis uniform single crystalline ZnO nanowire arrays and their functionalization with InP/ZnS core-shell quantum dots. The structures are characterized using electron microscopy, optical absorption, photoluminescence and Raman spectroscopy. Complementing photoluminescence, transmission electron microanalysis is used to reveal the successful QD attachment process and the atomistic interface between the ZnO and the QD. Energy dispersive spectroscopy reveals the co-localized presence of indium, phosphorus, and sulphur, suggestive of the core-shell nature of the QDs. The functionalized nanowire arrays are subsequently embedded in a poly-3(hexylthiophene) hole transport matrix with a high degree of polymer infiltration to complete the device structure prior to measurement.

InAs/GaSb superlattice pin photodiodes showing asymmetrical period design were fabricated by MBE on ptype GaSb substrate. These SL structures exhibited cut-off wavelength in the midwave infrared domain (MWIR) at 5μm at 80K. Electrical characterizations including dark current and capacitance-voltage measurements were performed on single detectors in the temperature range [77K-300K]. The SL photodiode measurements revealed carrier concentrations of about 6x10¹⁴ cm^-3 at 77K, dark current densities J= 4x10^-8 A/cm² at 77K, J = 0.19A/cm² at 200K and J = 10A/cm² at 300K for Vbias =-50mV. The measured R₀A product is higher than 1.5x106Ω.cm² at 77K and equal to 1x10^-2Ω.cm² at T=300K, for cut-off device equal to 5μm and 6.05μm, respectively. These results are compared with the ones obtained by symmetrical SL structure and show that the differential resistance area product is improved by more than one order of magnitude. These results obtained help us to define the optimized SL pin structure design suitable for high temperature operation in the MWIR domain.

A bariode is a new type of "diode-like" semiconductor photonic device, in which the transport of majority carriers is blocked by a barrier in the depletion layer, while minority carriers, created thermally or by the absorption of light, are allowed to pass freely across the device. In an n-type bariode, also known as an XB_nn structure, both the active photon absorbing layer and the barrier layer are doped with electron donors, while in a p-type bariode, or XB_pp structure, they are both doped with electron acceptors. An important advantage of bariode devices is that their dark current is essentially diffusion limited, so that high detector operating temperatures can be achieved. In this paper we report on MWIR n-type bariode detectors with an InAsSb active layer and an AlSbAs barrier layer, grown on either GaSb or GaAs substrates. For both substrate types, the bariodes exhibit a bandgap wavelength of ~ 4.1 μm and operate with Background Limited Performance (BLIP) up to at least 160K at F/3. Different members of the XBnn device family are investigated, in which the contact layer material, "X", is changed between n-InAsSb and p-GaSb. In all cases, the electro-optical properties of the devices are similar, showing clearly the generic nature of the bariode device architecture. Focal Plane Array detectors have been made with a pitch of 15 or 30μm. We present radiometric performance data and images from our Blue Fairy (320×256) and Pelican (640×512) detectors, operating at temperatures up to 180K. We demonstrate for both GaSb and GaAs substrates that detector performance can be achieved which is close to "Rule 07", the benchmark for high quality, diffusion limited, Mercury Cadmium Telluride (MCT) devices.

We introduce a power-law approximation to model non-linear ranges of the thermal conductivity, and under this approximation derive a simple analytical expression for calculating the temperature profile in high power quantum cascade lasers and light emitting diodes. The thermal conductivity of a type II InAs/GaSb superlattice (T2SL) is used as an example, having negative or positive power-law exponents depending on the thermal range of interest. The result is an increase or decrease in the temperature, respectively, relative to the uniform thermal conductivity assumption.

Quantum dot infrared photodetectors have generated a lot of interest in the recent past due to their potential for low dark current and high operating temperature. We demonstrate the use of thin AlGaAs barrier layers in the quantum dots in a well (DWELL) heterostructure to enhance the quantum confinement of carriers in the excited energy level. By controlling the excited state energy of the DWELL structure between the confinement enhancing (CE) barriers and near the continuum level of the barrier between the stacks, high quantum confinement as well as high escape probability for the photoexcited carriers has been obtained. High responsivity and detectivity of 6.5x10¹⁰ cm.Hz^1/2W^-1 (77K, 0.6V, 7.5mm, f/2), a factor of 10 improvement over a control sample without the CE barriers has been measured. The effect of changing the quantum well thickness and quantum dot size is also reported.

Recently, the type-II InAs/GaSb superlattice (T2SL) material platform is considered as a potential alternative for HgCdTe technology in long wavelength infrared (LWIR) imaging. This is due to the incredible growth in the understanding of its material properties and improvement of device processing which leads to design and fabrication of better devices. In this paper, we report electrical low frequency noise measurement on a high performance type-II InAs/GaSb superlattice 1024×1024 LWIR focal plane array.

We report our recent efforts on advancing of antimonide superlattice based infrared photodetectors and demonstration of focal plane arrays based on a complementary barrier infrared detector (CBIRD) design. By optimizing design and growth condition we succeeded to reduce the operational bias of CBIRD single pixel detector without increase of dark current or degradation of quantum efficiency. We demonstrated a 1024×1024 pixel longwavelength infrared focal plane array utilizing CBIRD design. An 11.5 μm cutoff focal plane without anti-reflection coating has yielded noise equivalent differential temperature of 53 mK at operating temperature of 80 K, with 300 K background and cold-stop. Imaging results from a recent 10 μm cutoff focal plane array are also presented. These results advance state-of-the art of superlattice detectors and demonstrated advantages of CBIRD architecture for realization of FPA.

High resolution multi-band infrared detection of terrestrial objects is useful in applications such as long range and high altitude surveillance. In this paper, we present a 640 by 512 type-II superlattice focal plane array (FPA) in the long-wave infrared (LWIR) suitable for such purposes, featuring 100% cutoff wavelengths at 9.5μm (blue channel) and 13μm (red). The dual band camera is single-bump hybridized to an Indigo 30μm pitch ISC0905 read-out integrated circuit. Test pixels revealed background limited behavior with specific detectivities as high as ~5x10¹¹ Jones at 7.9μm (blue) and ~1x10¹¹ Jones at 10.2μm (red) at 77K.

Free-space optical communication is a promising solution to the "last mile" bottleneck of data networks. Conventional near infrared-based free-space optical communication systems suffer from atmospheric scattering losses and scintillation effects which limit the performance of the data links. Using mid-infrared, we reduce the scattering and thus can improve the quality of the data links and increase their range. Because of the low scattering, the data link cannot be intercepted without a complete or partial loss in power detected by the receiver. This type of communications provides ultra-high bandwidth and highly secure data transfer for both short and medium range data links. Quantum cascade lasers are one of the most promising sources for mid-wavelength infrared sources and Type-II superlattice photodetectors are strong candidates for detection in this regime. The same way that that low scattering makes mid-wavelength infrared ideal for secure free space communications, high scattering can be used for secure short-range free-space optical communications. In the solar-blind ultraviolet (< 280 nm) light is strongly scattered and absorbed. This scattering makes possible non-line-of-sight free-space optical communications. The scattering and absorption also prevent remote eavesdropping. III-Nitride based LEDs and photodetectors are ideal for non-line-of-sight free-space optical communication.

One of the biggest challenges of improving the electrical performance in Type II InAs/GaSb superlattice photodetector is suppressing the surface leakage. Surface leakage screens important bulk dark current mechanisms, and brings difficulty and uncertainty to the material optimization and bulk intrinsic parameters extraction such as carrier lifetime and mobility. Most of surface treatments were attempted beyond the mid-infrared (MWIR) regime because compared to the bulk performance, surface leakage in MWIR was generally considered to be a minor factor. In this work, we show that below 150K, surface leakage still strongly affects the electrical performance of the very high bulk performance p-π-M-n MWIR photon detectors. With gating technique, we can effectively eliminate the surface leakage in a controllable manner. At 110K, the dark current density of a 4.7 μm cut-off gated photon diode is more than 2 orders of magnitude lower than the current density in SiO₂ passivated ungated diode. With a quantum efficiency of 48%, the specific detecivity of gated diodes attains 2.5 x 10¹⁴ cmHz^1/2/W, which is 3.6 times higher than that of ungated diodes.

Exploring the novel application to the quantum optics, the periodic crystallographic-polarity-inverted GaN waveguides were fabricated. In addition to the successful periodic reversal of the crystallographic orientations, periodic grating structures were formed on the surface due to the slight difference in the growth rates for different polarities, which gives the occurrence of the well-known photonic band structures. In this work, basic optical properties were investigated utilizing the variable-angle optical reflectance measurements on these waveguides with one-dimensional periodic grating structures, in order to obtain their photonic band structures. In addition to the optical interference fringes, clear reflectance dips originated from the resonance between the incident light and allowed waveguide modes appeared, aside from a weak resonant feature due to the coupling of the diffracted light to the evanescent mode on the grating surface, known as Wood's anomalies. Taking into account the refractive index dispersions and the zone-folding effects invoked by the grating, the origins of all the resonant features are successfully elucidated. Especially in case of resonant coupling to the waveguide modes, the corresponding orders of both the grating diffractions and the guided modes are assigned. Based on these assignments, the possible configurations of the wavelength conversions are discussed.

Engineered substrates such as large diameter (100mm) GaSb wafers need to be ready years in advance of any major shift in DoD and commercial technology, and typically before much of the rest of the materials and equipment for fabricating next generation devices. Antimony based III-V semiconductors are of significant interest for advanced applications in optoelectronics, high speed transistors, microwave devices, and photovoltaics. GaSb demand is increasing due to its lattice parameter matching of various ternary and quaternary III-V compounds, as their bandgaps can be engineered to cover a wide spectral range. For these stealth and spaced based applications, larger format IRFPAs benefit clearly from next generation starting substrates. In this study, we have manufactured and tested 100mm GaSb substrates. This paper describes the characterization process that provides the best possible GaSb material for advanced IRFPA and SLS epi growth. The analysis of substrate by AFM surface roughness, particles, haze, GaSb oxide character and desorption using XPS, flatness measurements, and SLS based epitaxy quality are shown. By implementing subtle changes in our substrate processing, we show that a Sb-oxide rich surface is routinely provided for rapid desorption. Post-MBE CBIRD structures on the 100mm ULD GaSb were examined and reveals a high intensity, 6.6nm periodicity, low (15.48 arcsec) FWHM peak distribution that suggests low surface strain and excellent lattice matching. The Ra for GaSb is a consistent ~0.2-4nm, with average batch wafer warp of ~4 μm to provide a clean, flat GaSb template critical for next generation epi growth.

In this paper we describe the crystal growth and surface characterisation of ultra-flat 4" GaSb substrates suitable for the epitaxial deposition of advanced infrared detectors. Results will be presented on the production of single crystal 4" GaSb ingots grown by a modified version of the liquid encapsulated Czochralski (LEC) technique , supported by the analysis of bulk material quality by dislocation Etch Pit Density (EPD) and X-Ray topography (XRT) assessments. This study will also describe how various techniques were used to characterize the quality of the bare substrate. Surface oxide properties of the GaSb substrates will be characterized by spectroscopic ellipsometry (SE). Bow, Warp and Total Thickness Variation (TTV) data will be presented for 4" wafers processed on a multiwafer-type polishing platform. This study will conclude with a 'blueprint' for the manufacture of large diameter GaSb substrates, this defining the requirements for the production use of GaSb within a commercial epitaxial wafer foundry.

As size requirements and pixel viabilities for infrared focal plane arrays (IRFPAs) continue to increase, resolution and sensitivity requirements for high performance advanced imaging systems must meet or surpass stringent demands. Strain layer superlattice (SLS) grown by molecular beam epitaxy (MBE) on 100mm GaSb has necessitated changes in crystal processing and finishing parameters. Device layer growth typically requires a thin (2-5 nm) and highly desorbable surface oxide on very flat substrates for successful MBE. This study compares the ability for rapid pre-epi desoprtion of three different chemo-mechanical (CMP) finishes on 100mm n:GaSb: CMP-1 with sequential double side polished (DSP), CMP-2 with sequential DSP, and CMP-2 with simultaneous double side polished (S-DSP). X-ray photoelectron spectroscopy (XPS) reveals the improvement from a CMP-1 (Ga-oxide rich) to CMP-2 (Sb-oxide rich) surface. No difference in surface chemistry was found between the CMP-2 of the sequential vs. simultaneous DSP. Tropel flatness measurements of the 100mm n:GaSb substrates show that both DSP and SDSP substrate batches yield excellent (<5μm) wafer warp. However, initial studies have shown a more consistent wafer flatness with use of the simultaneous-DSP process. MBE growth on the Sb-rich surface was examined by high resolution XRD and resulted in a 64.7A periodicity and excellent FWHM (~20 arcsec) which verified the GaSb surface finish effectiveness. The resultant surface finish and flatness may provide a benefit for larger diameter GaSb IRFPA applications.

Antimony-based photodetector materials have attracted considerable interest for their potential and demonstrated performance in infrared detection and imaging applications. Mid-wavelength infrared detector has been demonstrated using bulk InAsSb/AlAsSb-based nBn structures. Heterostructures based on InAs/Ga(In)Sb strained layer superlattices create a type-II band alignment that can be tailored to cover a wide range of the mid- and long-wavelength infrared absorption bands by varying the thickness and composition of the constituent materials. Through careful design, these Sb-based detectors can realize desirable features such as higher operating temperature, better uniformity, suppression of Auger recombination, reduction of tunneling currents, and higher quantum efficiency. The manufacturing challenge of these structures is the reproducible growth of high-quality Sb-based epiwafers due to their complex designs including large numbers of alternating thin layers and mixed group-V elements. In this paper, we discuss the manufacturability of such epiwafers on 3" and 4" diameter GaSb substrates by molecular beam epitaxy using multi-wafer production tools. Various techniques were used to characterize the material properties of these wafers, including high-resolution x-ray diffraction, low-temperature photoluminescence, Nomarski optical microscopy, and atomic force microscopy.

Systems for 3D image acquisition are the enabling technology for a number of applications such as architectural studies, safety and security, automotive. Single-sensor active-illumination cameras are the most promising system, ensuring a good depth measurement accuracy combined with a simple structure (no double sensor required), simplest measurement algorithm and night and daytime operation. These systems are based on the measurement of the time delay between the emission of light signal and the detection of the back-reflected signal (Time of Flight - TOF). The direct measurement of the time delay between two adjacent pulses is called direct TOF (dTOF), while if the time delay is obtained starting from the phase delay of a periodic waveform we speak of indirect TOF (iTOF). We present two different 0.35μm CMOS Silicon mini-arrays for iTOF 3D ranging based on square and sinusoidal waveforms, in which the sensitive element is a Single-Photon Avalanche Diode (SPAD).

In the last years many progresses have been made in the field of Silicon Single Photon Avalanche Diodes (SPAD) thanks to the improvements both in device design and in fabrication technology. For example, the use of custom fabrication processes has allowed a steadily improvement of SPAD performance in terms of active area diameter, Dark Count Rate (DCR), and Photon Detection Efficiency (PDE). Although a significant breakthrough has been achieved with the recent introduction of a new device structure capable of combining a good timing resolution with a remarkable PDE in the near infrared region, nevertheless there is still room for further improvements. In this paper we will discuss further modifications to the device structure enabling the fabrication of arrays with red enhanced photon detection efficiency.

The 3 to 4 μm range had long appeared inaccessible to quantum well lasers made on GaSb. Despite having excellent performance in the 2 to 3 μm range, GaInAsSb/AlGaAsSb quantum well lasers rapidly show their limits when crossing the 3 μm barrier (the highest wavelength reached with such a device was 3.04 μm under cw operation at 20°C). This situation was all the more regrettable because several gases have their strongest absorption lines in the 3 to 4 μm range: methane, for example, has a peak of absorption at 3.26 μm overhanging a weaker peak at 2.31μm by a factor 40. Works carried out in the University of Munich in 2005 gave new hopes to the world of laser diode spectroscopy. By replacing the quaternary AlGaAsSb barrier by a quinary AlGaInAsSb barrier, researchers were able to reach laser operation at 3.26 μm and room temperature in the pulsed mode. Since then, several teams have engaged in the objective of reaching cw operation at room temperature with such structures. We will give an insight into the phenomena responsible for the increase of threshold current with growing wavelength. Finally, we will present results obtained with a monomode DFB laser diode emitting at 3.37 μm having a threshold current of 140 mA at 18°C.

The interband cascade laser (ICL) is a unique device concept that combines the effective parallel connection of its multiple-quantum-well active regions, interband active transitions, and internal generation of electrons and holes at a semimetallic interface within each stage of the device. The internal generation of carriers becomes effective under bias, and the role of electrical injection is to replenish the carriers consumed by recombination processes. Major strides have been made toward fundamentally understanding the rich and intricate ICL physics, which has in turn led to dramatic improvements in the device performance. In this article, we review the physical principles of the ICL operation and designs of the active region, electron and hole injectors, and optical waveguide. The results for state-of- the-art ICLs spanning the 3-6 μm wavelength range are also briefly reviewed. The cw threshold input powers at room temperature are more than an order of magnitude lower than those for quantum cascade lasers throughout the mid-IR spectral range. This will lengthen battery lifetimes and greatly relax packaging and size/weight requirements for fielded sensing systems.

Silicon emission in and out resonant coupling with a high Q optical mode is studied in a microdisk cavity with emissive W-centers. Results show that the W-centers photoluminescence intensity in a silicon microdisk is one order of magnitude higher than that in the substrate. It exhibits a maximum when emission line and cavity mode frequencies are matched.

Selected results obtained in the framework of MBE grown nanostructure for photonics on silicon are repsented in this paper. We present first a comprehensive study of GaAsPN/GaPN quantum wells (QWs) grown onto GaP substrates, in the light of a comparison with their N-free GaAsP/GaP QWs counterpart system. High density of small InGaAs/GaP Quantum Dots are presented next with their PL properties. Finally, RT photoluminescence properties of GaAsPN/GaPN QWs onto Si substrate are presented and discussed in term of carrier injection efficiency. However, for future development, optical properties of the active area must be improved and are tightly bound to the structural perfection of the GaP/Si template layer. To address this point, structural analyses including X-Ray Diffraction (lab setup and synchrotron) and Transmission Electron Microscopy have been performed, with a particular care for typical III-V/Si defect characterisation. First results of Si buffer layer growth are also presented as a perspective for future low defect MBE grown GaP/Si template layers.

Integration of semiconductor laser diodes on Si substrates will allow the realization of complex photonics circuits with new functionalities. A promising way to combine the well known Si technology with III-V semiconductors is the direct growth of the Sb-based materials. Indeed, GaSb, AlSb, InAs and their related alloys offer a large range of band-gaps and band-offsets. High performance Sb-based lasers and detectors operating in the mid-infrared wavelength range as well as high speed and low consumption field effect transistors have already been demonstrated using these materials. We investigated the potential of GaSb-based lasers grown by molecular beam epitaxy onto Si substrate. With standard design and technology we demonstrate pulsed laser operation at room temperature from the telecom wavelength range (1.5 μm) to the mid-IR (2.3 μm). A new structure design with a dedicated technology process allows cw lasing at room temperature.

Besides microcavities and photonic crystals, photonic nanowires have recently emerged as a novel resource for solidstate quantum optics. We will review recent studies which demonstrate an excellent control over the spontaneous emission of InAs quantum dots (QDs) embedded in single-mode GaAs photonic wires. On the basic side, we have demonstrated a strong inhibition (x 1/16) of QD SpE in thin wires (d<λ/2n), a nearly perfect coupling of the SpE to the guided mode (β>0.95 for d~λ/n), and polarization control in elliptical nanowires. A single QD in a photonic wire is thus an attractive system to explore the physics of the "one-dimensional atom" and build novel quantum optoelectronic devices. Quite amazingly, this approach has for instance permitted (unlike microcavity-based approaches) to combine for the first time a record-high efficiency (72%) and a negligible g⁽²⁾ in a QD single photon source.

Analysis of complex quantum systems having many partitions is a very complicated numerical task. As the number of entities increase, the computational burden blows up and at the same time accuracy is lost due to integration in timedomain. Here, we present a systematic and rigorous methodology to deal with the multi-partite quantum systems comprised of many quantum dots with arbitrary transition oscillator strengths as well as dipole-dipole interaction. No limit is imposed on the number of radiation modes in the interacting reservoir. We present an exact solution to this system and also a general self-generating automated code which is capable of solving the system in time-domain with full accuracy and maximal computational efficiency. The code is also able to compute the exact concurrency as the measure of entanglement. Various coupling regimes ranging from the weak to ultrastrong are analyzed and discussed.

We present standoff detection of various explosives by backscattering spectroscopy, using a sensing system based on mid-IR external-cavity quantum cascade lasers (EC-QCL) with a broad tunable range of about 300 cm^-1. Traces of TNT (trinitrotoluene), PETN (pentaerythritol tetranitrate) and RDX (cyclotrimethylenetrinitramine) as well as different nonhazardous substances were investigated by illuminating them with the EC-QC laser and collecting the diffusely backscattered light. Tuning the EC-QCL across the characteristic absorption spectra enables us to detect and identify the explosives against a background of non-hazardous materials.

We present a study of the spectral and angular dependence of the diffuse scatter of mid-infrared (MIR) laser light from explosives residues on surfaces. Experiments were performed using an external cavity quantum cascade laser (ECQCL) tunable between 7 and 8 μm (1270 to 1400 cm^-1) for surface illumination. A mercury cadmium telluride (MCT) detector was used to detect backscattered spectra as a function of surface angle at a 2 meter standoff. A ferroelectric focal plane array was used to build hyperspectral images at a 0.5 meter standoff. Residues of RDX, tetryl, and TNT were investigated on surfaces including a painted car door for angles between zero (specular) and 50 degrees. We observe spectral signatures of the explosives in the diffuse scattering geometry which differ significantly from those observed in transmission geometries. Characterization of the scattered light spectra of explosives on surfaces will be essential for understanding the performance of standoff explosives detection instruments and developing robust spectral analysis techniques.

Block Engineering has developed a widely tunable quantum cascade laser (QCL) spectrometer, a probe, and algorithms specific to detecting low levels of surface contamination. This paper discusses the basic technology of the QCL spectrometer both in a standoff and probe based configuration. It provides information on the algorithms and probes developed for this application. The paper compares the QCL based technique to other approaches for detecting surface contamination.

Sensitive and fast identification of drugs or drug precursors is important and necessary in scenarios like baggage or container check by customs or police. Fraunhofer IPM is developing a laser spectrometer using external cavity quantum cascade lasers (EC-QCL) to obtain mid-infrared (IR) absorption spectra in the wavelength range of the specific vibrational bands of amphetamines and their precursors. The commercial EC-QCL covers a tuning range of about 225 cm^-1 within 1.4 s. The system could be used for different sample types like bulk samples or liquid solutions. A sampling unit evaporates the sample. Because of small sample amounts a 3 m long hollow fiber with an inner volume smaller than 1ml is used as gas cell and wave guide for the laser beam. This setup is suitable as a detector of a gas chromatograph instead of a standard detector (TCD or FID). The advantage is the selective identification of drugs by their IR spectra in addition to the retention time in the gas chromatographic column. In comparison to Fourier Transform IR systems the EC-QCL setup shows a good mechanical robustness and has the advantage of a point light source. Because of the good fiber incoupling performance of the EC-QCL it is possible to use hollow fibers. So, a good absorption signal is achieved because of the long optical path in the small cell volume without significant dilution. In first laboratory experiments a detection limit in the microgram range for pseudo ephedrine is achieved.

Using infrared hyperspectral imaging, we demonstrate microscopy of small particles of the explosives compounds RDX, tetryl, and PETN with near diffraction-limited performance. The custom microscope apparatus includes an external cavity quantum cascade laser illuminator scanned over its tuning range of 9.13-10.53 μm in four seconds, coupled with a microbolometer focal plane array to record infrared transmission images. We use the hyperspectral microscopy technique to study the infrared absorption spectra of individual explosives particles, and demonstrate sub-nanogram detection limits.

We present new circuital solutions for operating InGaAs/InP SPADs at high speed with very fast avalanche quenching time. A compact wide-band pulse generator (mounted close to the detector) is able to gate the SPAD at a repetition frequency from 200 Hz up to 133 MHz. An adjustable amplitude gate-driver allows to trade-off between photon detection efficiency and dark count rate, while a variable gate-width precisely selects the time interval during which the detector is ON. A fast avalanche-quenching scheme, working on both SPAD's anode and cathode, is able to minimize quenching action to less than 1 ns, thus effectively reducing afterpulsing through a decreased total charge flowing through the junction. We integrated all such circuits into a compact detection module, together with a previouslyreported differential read-out electronics for low time-jitter response. The performance of the overall module is good in many different setting points, thus being able to satisfy a wide variety of applications.

We present a compact instrument able to quickly time-gate a silicon Single-Photon Avalanche Diode (SPAD) to be used in advanced gated Time-Correlated Single-Photon Counting (TCSPC) setups, like time-resolved optical spectroscopy, optical mammography, optical molecular imaging. The detection module can be used to boost the photon counting dynamic range, thanks to the fast transitions between the OFF and the ON state of the detector. The module embeds into a single box (11 cm x 15 cm x 24 cm) all components needed to operate a SPAD detector in fast time-gated mode and to output a standard NIM timing signal. The module includes: i) an ultra-fast pulse generator, based on MMIC components, to enable and disable the detector in less than 200 ps for very short and well-defined time slots, ranging from less than 1 ns up to 10 ns with 10 ps steps, at a repetition rate up to 50 MHz; ii) the silicon SPAD itself together with optical assembly to focus photons from an optical fiber onto the active area; iii) a passive quenching/active reset electronics, needed for optimal detector operation; iv) a low time-jitter comparator, to detect avalanche ignitions with less than 30 ps (FWHM) jitter and to generate a standard NIM output; v) a service board containing power supply, microcontroller, and USB link, to remotely set and control all instrument parameters.

Superconducting nanowire single photon detectors (SNSPD) have unique characteristics of ultra low dark counts and wide spectrum sensitivity. These natures are indispensable for the evaluation of ultra-broadband parametric fluorescence, which are used for the quantum optical coherence tomography and novel optical non-linear experiments. Here we report the spectral dependence of the detection efficiency of a meander type SNSPD device, having reduced strip width of 50 nm, over a wide spectrum range up to near infra-red wavelength. The fiber coupled, meander type device was fabricated using 6 nm thick Niobium nitride (NbN) nanowires of reduced strip width, 50 nm, patterned over a MgO substrate with active area of 10 x 10 μm². A maximum efficiency of 32% at 500 nm, 30% at 600 nm, 16% at 800 nm, 10% at 1000 nm, and 1% at 1550 nm with the normalized bias current of 0.95 (bias 37 μA ) was observed at 4.2 K. The salient feature of the device is, it exhibits a very low dark count rate (DCR) of only 2 Hz at the standard operating bias of 37 μA and ultra low DCR of 0.01Hz at 34 μA. Moreover, at this reduced bias with 0.01Hz DCR, the detection efficiency is not appreciably decreased in the visible region (32% at 500 nm and 30% at 600 nm) and an order decrease is observed (0.1%) at 1550 nm. The noise equivalent power (NEP) is of the order 10^{-19 WHz-1/2} in the visible region and 10^-17 WHz^{- 1/2} in the near IR region. Ultra-broad band parametric fluorescence of band width from 791 nm to 1610 nm generated by a quasi-phase matched (QPM) device was successfully detected with this SSPD.

Micro-size light emitting diode (μLED) arrays based on III-nitride semiconductors have emerged as a promising technology for a wide range of applications. If InGaN μLED arrays can be integrated on to Si complementary metal-oxide-semiconductor (CMOS) substrates for active driving, these devices could play crucial roles in ultra-portable products such as next generation pico-projectors, as well as in emerging fields such as biophotonics and optogenetics. Here we present a demonstration of, and methods for, creating a highresolution solid-state self-emissive microdisplay based on InGaN/GaN semiconductors. An energy efficient active drive scheme is accomplished by integrating micro-emitter arrays with CMOS active matrix drivers that are flip-chip bonded together via indium metal bumps.

The flexible GaN-based light emitting diode (LED) has been fabricated on a plastic substrate for flexible display applications. The epitaxial structures of the GaN LED arrays are transferred onto a flexible substrate using standard soft lithography technology and connected to a source-meter by metal lines. To verify the mechanically and optically stable characteristics of the GaN LEDs on the flexible substrates, the electrical properties are characterized during 2000 bending cycles at various bending radius. A white light-emitting phosphor-coated GaN LED shows its potential as a next-generation flexible light source.

Recent developements for highly efficient ligth emitting diodes are introduced. Multi-quantumwell structure to improve the internal quantum efficiency, chip fabrication techniques to increase the extraction efficiency, and packaging techniques with phosphor distribution optimization are combined to obtain the efficient LEDs. Comparison between the several leading products in the market has been performed to reveal the current LED techniques. The internal quantum efficiency is found to be related to not only the dislocation density, but also the defect size and type. Some key factors are reviewed on the reliability of LEDs which recently has been improved a lot. For general lighting application, LM-80 test becomes the industry standard and will be introduced briefly.

The electrical resistivity of monolayer graphene exhibit significant changes upon expose to different concentration of oxygen (O2) at room temperature. The monolayer graphene, grown by chemical vapor deposition (CVD) with perfect uniformity within 1cm×1cm will attach O₂ molecules which will act as a p-type dopant and enhance the hole conductivity, make a change of resistivity of graphene thin film. We quantified the change of resistivity of graphene versus different O₂ concentration and the detection limit of the simple O₂ sensor was 1.25% in volume ratio.

Two-photon absorption in GaAs occurs once two photon impinge on the semiconductor surface within the virtual state lifetime, i.e. few fs. Two photon conductivity (TPC) in GaAs is thus particulary well fitted to measure photon coincidence rates in the femtosecond range. Using this new TPC technique we have evidenced various original quantum properties of light, such as photon bunching in thermal light and extrabunching of twin beams. This technique opens new avenues in quantum optics, for quantum cryptography, ghost imaging or non linear optics.

The miniaturization of quantum information technology is a subject attracting a growing attention. The exploitation of spontaneous parametric down conversion in AlGaAs waveguides to generate photon pairs presents several advantages: high nonlinear susceptibility, room-temperature operation and high emission directionality in the telecom range. In this work we will present our recent results on three different kinds of AlGaAs devices: a selectively oxidized source based on form birefringence, a waveguide based on modal phase matching and a microcavity-based source based on counterpropagating phase matching. We will discuss and compare the figures of merit characterizing the three devices for quantum communication applications.

We show that it is possible to fix the carrier phase of a quantum cascade laser (QCL) by using injection seeding. Terahertz (THz) pulses with a fixed phase are injected into the QCL cavity and coincide with the gain of the QCL being turned on rapidly to avoid gain clamping (gain switching). The externally injected THz pulses are greatly amplified through multiple passes and can initiate laser action (instead of the spontaneous emission) and set the carrier-phase. Consequently, as well as the generation of large THz fields, this enables the electric field of the laser emission to be measured as a function of time, from initiation of lasing to the steady-state lasing regime using coherent sampling techniques. The phased-resolved field of the QCL is thus directly measured in the time-domain. This work enables the laser emission to be measured in the time domain and the QCL to be used as a powerful source for time-domain spectroscopy. We also use this scheme to imprint a fixed phase relationship between the multiple longitudinal modes of a THz QCL, resulting in the emission of ultrashort THz laser pulses.

Resonant tunneling diode (RTD) is an electronic device embodying a unique quantum-interference phenomenon: negative differential resistance (NDR). Compared to other negative resistance devices such as (Esaki) tunnel and transferred-electron devices, RTDs operate much faster and at higher temperatures. III-nitride materials, composed of AlGaInN alloys, have wide bandgap, high carrier mobility and thermal stability; making them ideal for high power high frequency RTDs. Moreover, larger conduction band discontinuity promise higher NDR than other materials (such as GaAs) and room-temperature operation. However, earlier efforts on GaN-based RTD structures have failed to achieve a reliable and reproducible NDR. Recently, we have demonstrated for the first time that minimizing dislocation density and eliminating the piezoelectric fields enable reliable and reproducible NDR in GaN-based RTDs even at room temperature. Observation of NDR under both forward and reverse bias as well as at room and low temperatures attribute the NDR behaviour to quantum tunneling. This demonstration marks an important milestone in exploring III-nitride quantum devices, and will pave the way towards fundamental quantum transport studies as well as for high frequency optoelectronic devices such as terahertz emitters based on oscillators and cascading structures.

Self-assembled nanowires represent a new interesting technology to be explored in order to increase the cut-off frequency of electronic THz detectors. They can be developed in field effect transistor (FET) and diode geometries exploiting non-linearities of either the transconductance or the current-voltage characteristic as detection mechanism. In this work we demonstrate that semiconductor nanowires can be used as building blocks for the realization of highsensitivity terahertz one-dimensional FET detectors. In order to take advantage of the low effective mass and high mobilities achievable in III-V compounds, we have used InAs nanowires, grown by vapor-phase epitaxy, and properly doped with selenium to control the charge density and to optimize source-drain and contact resistance. The detection mechanism exploits the non-linearity of the transconductance: the THz radiation field is fed at the gate-source electrodes with wide band antennas, and the rectified signal is then read at the drain output in the form of a DC voltage. Responsivity values as large as 1 V/W at 0.3 THz have been obtained, with noise equivalent powers (NEP) < 2 × 10^-9 W/√Hz at room temperature. The large existing margins for technology improvements, the scalability to higher frequencies, and the possibility of realizing multi-pixel arrays, make these devices highly competitive as a future solution for THz detection.

We report on the application of an innovative spectroscopic balancing technique to measure isotopologue abundance quantification. We employ quartz enhanced photoacoustic spectroscopy in a 2f wavelength modulation mode as an absorption sensing technique and water vapor as a test analyte. Isotope absorption lines with very close lower energy levels and with the same quantum numbers have been selected to limit the sensitivity to temperature variations and guarantee identical broadening relaxation properties. A detection sensitivity in measuring the deviation from a standard sample δ¹⁸O of 1.4%_o, in 200 sec of integration time was achieved.

A novel heterodyne-enhanced Faraday rotation spectroscopic (H-FRS) system for trace gas detection of nitric oxide (NO) is demonstrated. The system is based on a quantum cascade laser emitting at ~5.2 μm and a mercury cadmium telluride photodetector (both thermoelectrically cooled). The heterodyne detection is performed at 30MHz, where the laser relative intensity noise is significantly smaller than at low frequencies. With an implementation of active interferometer stabilization technique, the current system shows total noise level that is only 5.4 times above the fundamental shot-noise limit and the Faraday rotation angle sensitivity of 2.6 × 10^-8 rad/√Hz. The NO detection limit of 30.7 ppb-v/√Hz was achieved for the R(8.5)e NO transition using 100 Gauss magnetic field and 0.15 m optical path length.

A multi-channel laser-based chemical sensor platform is presented, in which a modular architecture allows the exchange of complete sensor channels without disruption to overall operation. Each sensor channel contains custom optical and electronics packages, which can be selected to access laser wavelengths, interaction path lengths and modulation techniques optimal for a given application or mission. Although intended primarily to accommodate mid-infrared external cavity quantum cascade lasers and astigmatic Herriott cells, channels using visible or near infrared lasers or other gas cell architectures can also be used, making this a truly versatile platform. Analog and digital resources have been carefully chosen to facilitate small footprint, rapid spectral scanning, low-noise signal recovery, fail-safe autonomous operation, and in-situ chemometric data analysis, storage and transmission. Results from the demonstration of a two-channel version of this platform are also presented.

Ultra-sensitive detection of nitrogen dioxide (NO₂) in the ν3 fundamental band of NO₂ using Faraday Rotation Spectroscopy (FRS) based optical sensor platform is reported. The FRS technique is well suited for selective trace gas measurements of paramagnetic species including the prominent air pollutants such as NO or NO₂. In this paper a widely tunable external cavity quantum cascade laser (EC-QCL) is employed as an excitation source. The available EC-QCL mode-hop free tuning range between 1600 cm^-1 and 1650 cm^-1 allows to access the optimum for FRS technique 4₄₁<-4₄₀ Q-branch NO₂ transition at 1613.2 cm^-1 with an optical power of ~135 mW. In order to improve detection sensitivity and reduce size of the sensor platform, a custom made 22.47 cm long Herriott multipass gas cell (MPC) with a total effective optical path of 10.1 m was implemented. For a MPC configured NO₂ FRS sensor operating in line-scanning mode a minimum detection limit of 1.6 ppbv (1σ) and 0.15 ppb (1σ) is achieved for a 1 sec and 100 sec averaging time, respectively. Preliminary results for long term measurements of atmospheric NO₂ for the FRS sensor operating at an optimal pressure of 30 Torr and magnetic field of 200 Gaussrms were demonstrated.

Many gas-phase sensing applications involve detection of multiple molecules with rotationallyresolved spectra. The benefits of using mid-infrared (3 - 20 μm) radiation for detection are clear: strong, characteristic absorption features across regions with varying degrees of overlap can be exploited for multi-component detection. Quantum cascade lasers now provide CW radiation throughout the mid-infrared, but there are no commercial lasers available that meet the combined requirements of small size, low power consumption, and continuous broad tuning. Recent progress in realizing these modules is discussed, along with commercial applications enabled by the technology.

We review our last results in the field of quantum imaging obtained at INRIM.

In the last few years infrared focal plane arrays based on Type-I GaAs/AlGaAs quantum well infrared photodetectors (QWIPs) have been commercialized, providing excellent cost-effective imaging for security and surveillance and gas imaging applications. A second cooled infrared sensor technology that has made significant advances in recent years is photodiodes based on Type-II InAs/(In)GaSb strained layer superlattices (SLS). Imaging chips with upto a million pixels, quantum efficiency exceeding 50%, and cutoff wavelength exceeding 10 microns have been recently demonstrated. SLS offers the promise of the high quantum efficiency and operating temperature of longwave infrared mercury cadmium telluride (MCT) at the price point of QWIP and midwave infrared indium antimonide (InSb). That promise is rapidly being fulfilled. This paper presents the current state-of-the-art of both these sensor technologies at this critical stage of their evolution.

Since 2005, Thales is successfully manufacturing QWIPs in high rate production through III-V Lab. All the early claimed advantages of QWIPs are now demonstrated. The versatility of the band-gap engineering allows the custom design of detectors to fulfill specific application requirements in MWIR, LWIR or VLWIR ranges. The maturity of the III-V microelectronics based on GaAs substrates gives uniformity, stability and high production rate. In this presentation we will discuss the specific advantages of this type of detector. An overview of the available performances and production status will be presented including under-development products such as dual band and polarimetric sensors.

Multiband infrared focal plane arrays (FPAs) with small pixel pitch have increased device processing complexity since they often need more than two terminals per pixel for readouts. Simpler FPAs are enabled by our newly demonstrated optically-addressed two-terminal multiband photodetector architecture. For long-wavelength infrared (LWIR) and midwavelength infrared (MWIR) imaging applications, the use of quantum well infrared photodetectors (QWIP) has been investigated. The results show that the utilization of unipolar QWIPs with bipolar near infrared (NIR) devices is feasible with this new optical-addressing scheme. Potential device performance is analyzed with an equivalent AC circuit model. Proposed design maximizes fill factor and enables small pixel-pitch FPA with single indium-bump per pixel for NIR/MWIR/LWIR multiband detection capability.

Rigorous electromagnetic field modeling is applied to calculate the quantum efficiency (QE) of various quantum well infrared photodetector (QWIP) geometries. We found quantitative agreement between theory and experiment for linear grating coupled QWIPs, cross-grating coupled QWIPs, corrugated-QWIPs, and enhanced-QWIPs. Also, the model adequately explains the spectral lineshapes of the quantum grid infrared photodetectors. Equipped with a quantitative model, we designed resonant cavities that are suitable for narrowband imaging around 8 - 9 microns. The results show that with properly designed structures, the theoretical QE can be as high as 78% for 25-micron pixel pitch arrays and 46% for 12-micron pixel pitch arrays. Experimental efforts are underway.

The development of GaAs quantum well infrared photodetectors (QWIPs) at NASA's Goddard Space Flight Center began in the late 1980s and has continued ever since. Initial developments produced single element detectors and shortly thereafter in 1990 a 128× 128 element array was developed in collaboration with AT&T Bell Labs and Rockwell Science Center. Since that time we have developed numerous generations of QWIP arrays most recently resulting in the multi-QWIP focal plane for the next NASA-US Geological Survey Landsat mission to be launched in December of 2012. This paper will describe the technological evolutionary process from concept to a space-flight qualified infrared detector system. Many developments have been accomplished in the ensuing two decades as well as numerous experiments, both ground-based and airborne en route to qualifying for a NASA space flight mission. Some of these experiments will also be described as well as our current development for the next generation of QWIP focal planes for potential earth observing missions.

Hexagonal boron nitride (hBN) has been recognized as an important material for various device applications and as a template for graphene electronics. Low-dimensional hBN is expected to possess rich physical properties, similar to graphene. The synthesis of wafer-scale semiconducting hBN epitaxial layers with high crystalline quality and electrical conductivity control is highly desirable. We report the successful synthesis of large area hBN epitaxial layers (up to 2-inch in diameter) by metal organic chemical vapor deposition. Ptype conductivity control was also attained by in-situ Mg doping. Compared to Mg doped wurtzite AlN, which possesses a comparable energy band gap (~6 eV), dramatic reductions in Mg acceptor energy level and p-type resistivity have been realized in hBN epilayers. Our results indicate that (a) hBN epitaxial layers exhibit outstanding semiconducting properties and (b) hBN is the material of choice for DUV optoelectronic devices. The ability of conductivity control and wafer-scale production of hBN opens up tremendous opportunities for emerging applications, ranging from revolutionizing p-layer approach in III-nitride deep ultraviolet optoelectronics to graphene electronics.

Metal-semiconductor-metal solar blind ultraviolet photodetectors have been fabricated using both BGaN-GaN and BGaN-AlN superlattices as active layers. A high internal gain (up to 3 × 10⁴ for optical power in the nW range) is obtained with a highly reduced dark current thanks to the boron incorporation. In the high optical power regime (W range), the time response is in the nanosecond range, which is much smaller than that of GaNand ZnO-based ultraviolet photodetectors. Moreover, the boron incorporation in GaN material allows the tuning of the cutoff wavelength.

Magneto-optics and nanophotonics offer promising developments for applications in various technological sectors like data manipulation and storage, bio-imaging or optical sensors. Towards such purposes we show that it is advantageous to combine ultrafast magnetism performed with ultrashort laser pulses together with nanophotonics performed on various magnetic materials. Firstly, we discuss the important physical mechanisms underlying the control of magneto-optical nanodevices with femtosecond laser pulses. Secondly, we give examples of magneto-optical patterning which can be used for switching or for realizing diffractive magneto-optics. For example, individual ferromagnetic CoPt3 dots can be manipulated at the femtosecond time scale using confocal magneto-optical Kerr microscopy. Alternatively one can pattern such dots and control their size and shape. Patterning magnetic arrays on ferromagnetic metals with light pulses is also potentially very attractive for diffractive structures. Thirdly, we describe the advantages of performing coherent magneto-optics. In particular, transparent magnetic materials like Garnets are well adapted for making self diffractive magneto-optical devices.

New boundary conditions are derived for tunnel-heterojunctions, where the effective Hamiltonian is a generic power of the momentum-operator. A novel expression of probability-current operator, which can be also applied in presence of the D'yakonov-Perel (DP) Hamiltonian, has to be used. We test our technique on the interface between two semi-infinite media, with on one side a free-electron-like material and on the other side the [110]- oriented GaAs barrier.

We present in this study a theoretical and experimental investigation of the MWIR HgCdTe nBn device concept. Theoretical work has demonstrated that the HgCdTe nBn device is potentially capable of achieving performance equivalent to the ideal double layer planar heterostructure (DLPH) detector. Comparable responsivity, low current denisty J_dark, and high detectivity *D values rival those of the DLPH device without requiring p-type doping. The theoretical results suggests that the HgCdTe nBn structure may be a promising solution for achieving a simplified MWIR device structure and addressing problems associated with reducing thermal generation in conventional p-on-n structures and processing technology limitations such as achieving low, controllable in-situ p-type doping with MBE growth techniques. Furthermore, the physical mechanisms for selective carrier conduction in the nBn structure may provide a basis to incorporate into future device structures to suppress intrinsic Auger carrier generation. Likewise, the experimental demonstration of the MWIR HgCdTe nBn devices introduces a promising potential alternative to conventional high performance p-n junction HgCdTe photodiodes. The experiments described in this study illustrate the successful implementation of a HgCdTe barrier-integrated structure. The measured current-voltage characteristics of planar-mesa and mesa HgCdTe nBn devices exhibit barrier-influenced behavior and follow temperature-dependent trends as predicted by numerical simulations. Optical measurements of the planar-mesa MWIR HgCdTe nBn device indicate a bias-dependent spectral response. Further changes to MWIR HgCdTe nBn layer structure has shown an over 10⁵ A/cm² reduction in J_dark as well as a shift to a lower turn-on operation bias. This experimental investigation highlights the potential for pursuing similar and related unipolar, type-I barrier devices for high performance infrared detector applications.

We describe the factors that go into the component choices for a short wavelength (SWIR) imager, which include the SWIR sensor, the lens, and the illuminator. We have shown the factors for reducing dark current, and shown that we can achieve well below 1.5 nA/cm² for 15 μm devices at 7°C. We have mated our InGaAs detector arrays to 640x512 readout integrated integrated circuits (ROICs) to make focal plane arrays (FPAs). In addition, we have fabricated high definition 1920x1080 FPAs for wide field of view imaging. The resulting FPAs are capable of imaging photon fluxes with wavelengths between 1 and 1.6 microns at low light levels. The dark current associated with these FPAs is extremely low, exhibiting a mean dark current density of 0.26 nA/cm² at 0°C. FLIR has also developed a high definition, 1920x1080, 15 um pitch SWIR sensor. In addition, FLIR has developed laser arrays that provide flat illumination in scenes that are normally light-starved. The illuminators have 40% wall-plug efficiency and provide low-speckle illumination, provide artifact-free imagery versus conventional laser illuminators.

HgTe colloidal quantum dot have been demonstrated for mid-infrared photoconduction. The potential and challenges associated to the materials are discussed.

This paper describes structural properties of strain-balanced InAs/InAs_1-xSb_x type-II superlattices (SLs) with random and modulated InAs/InAs_1-xSb_x alloy layers as grown on GaSb(001) substrates either by molecular beam epitaxy (MBE) or metalorganic chemical vapor deposition. The SL periods and the average Sb compositions of the InAs/InAs_1-xSb_x alloys are determined by comparison of simulations with (004) high-resolution X-ray diffraction (XRD) measurements. The most intense SL peaks no longer correspond to the zero-order peak because of the large SL periods, and XRD studies of thick individual InAs/InAs_1-xSb_x and InAs layers show envelope modulations of the SL peaks on either side of the substrate peak, causing some satellite peaks to be more intense than the zero-order SL peak. From the substrate - zero-order SL peak separations, the average SL strain in the growth direction is revealed to be less than ~0.2%. Calculated bandgap energies agree closely with photoluminescence peaks for mid-wavelength and long-wavelength infrared samples. Cross-sectional electron micrographs reveal the entire structure including the GaSb substrate and buffer layer, the SL periods, and the GaSb cap layer. Growth defects are occasionally visible, some originating at the substrate/buffer interface, some starting in the middle of the buffer layer, and some located only just within the SL. Higher magnification images of the SLs grown by MBE reveal that interfaces for InAs/InAs_1-xSb_x deposited on InAs are considerably more abrupt than those of InAs deposited on InAs/InAs_1-xSb_x with the most likely reason being segregation of the Sb surfactant during layer growth.

The strain distribution across interfaces in InAs/GaSb superlattices is investigated by scanning transmission electron microscopy (STEM), using an aberration corrected probe. Atomic resolution images of the superlattices (grown on (100)-GaSb substrates) were acquired using the high-angle annular dark field (HAADF) imaging technique. For quantitative strain analysis, the peak-pair algorithm was used to determine the local atomic displacements across interfaces and within individual layers in the structure. The measured displacements were then used to calculate the strain map with respect to a reference lattice in the GaSb-substrate region. To precisely identify the local regions in the strain map Fourier transformation of the HAADF-STEM image was performed to obtain the chemically-sensitive (200)- Fourier component of the image. A comparison of these images with strain profiles determined from the strain maps revealed that the GaSb-on-InAs interface is GaAs-like, with a tensile strain of - 0.018 ± 0.003, whereas the overall strain at the InAs-on-GaSb interface was negligible. In addition, the strain within the GaSb layers was found to be compressive, with a magnitude of 0.008 ± 0.003, indicating In incorporation in these layers.

We report the full electrooptical characterization of two MWIR InAs/GaSb superlattice (SL) pin photodiodes. The first one features a symmetrical period with 8 InAs monolayers (MLs) and 8 GaSb MLs, while the second one relies on an asymmetrical period with 7.5 InAs MLs and 3.5 GaSb MLs. This asymmetrical design was recently proposed by IES to both decrease the dark current (since it decreases the intrinsic carrier concentration) and increase the quantum efficiency (since it increases the wavefunctions overlap). We present dark current, noise, spectral response and quantum efficiency measurements. Our results confirm that the asymmetrical design allows to greatly improve the performance of MWIR SL pin photodiodes, with an improvement of more than one decade in terms of dark current and an improvement of a factor 1.5 in terms of quantum efficiency. The noise measurements under dark conditions show that the symmetrical (asymmetrical) sample remains Schottky noise-limited up to a bias voltage of -600mV (resp -800mV) and that 1/f noise remains very low.

Noise in quantum cascade detectors is studied experimentally and theoretically. Measurements were performed in dark conditions on a quantum cascade detector operating at 14.5 μm, in the very long wave infrared range. To investigate the signal-to-noise contributions of each intersubband transition involved in the transport, a model of noise has been developed. It is based on a noise equivalent electrical circuit of the quantum cascade detector. Non-radiative diagonal transitions (fundamental state to levels of the cascade structure) are identified as dominant contributions to the dark current and noise in the measured device. Based on these theoretical considerations, new optimized structures for the very long wave-infrared range are designed and exhibit a noise reduction down to a factor three at optimum responsivity.

Graphene is a promising material for optoelectronics and photonics. Recent experiments demonstrated graphene photodectectors based on interband transitions working at Mid and Near-IR/Visible regions. Extension of spectral range to longer wavelengths requires alternative photoresponse mechanisms. One of the mechanisms which has been proven to be efficient for THz detection in "classical" semiconductor materials is the optically-induced breakdown of quantum Hall effect. In our work we successfully demonstrated a graphene-based QHE photodetector. Our result demonstrates the potential of graphene as a material for Far-IR photodetectors. Further improvement in device design and use of more efficient radiation coupling solutions should enable graphene photodetectors with broader spectral range, higher sensitivity, and elevated operating temperatures for a variety of applications.