Infrared photodetectors fabricated from self-organized quantum dot nanostructures
Author(s):
Elias Towe;
Dongfeng Pan;
Stephen W. Kennerly
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Intersubband carrier transitions in either the conduction or valence bands of III-V semiconductors are important for the design of a new generation of optoelectronic devices. These transitions have been successfully used to demonstrate the operation of a new class of infrared lasers and detectors. In this paper, we discuss the use of intersubband transitions in quantum dot nanostructures for infrared sensing. The quantum dot structures in our work allow the detection of normal-incidence light. This is promising for the design of future focal plane arrays that do not require a grating structure to scatter incident light into the correct polarization for detection via intersubband transitions. The quantum dot infrared photodetectors in this work also exhibit an intrinsic photovoltaic effect. Both photoconductive and photovoltaic operation has been demonstrated at low temperatures (40 K) with responsivities on the order of tens of mA/W for bias voltages less than 0.5 V. Detectivities ranging from 2 X 108 cmHz1/2/W to 7 X 109 cmHz1/2/W have been measured in devices operating in either the photovoltaic or photoconductive mode. We have demonstrated that the quantum dot structures have the capability to detect infrared light in the 9 to 13 micrometers spectral band.
Intermixing-induced tunability in infrared-emitting InGaAs/GaAs quantum dots
Author(s):
Rosa Leon
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The effects of intermixing on the radiative emission from InGaAs/GaAs quantum dot (QD) structures with excited state luminescence are presented. Thermally induced compositional disordering of the InGaAs/GaAs interface had been used to blue-shift all peaks and tune their intersublevel energy spacings ((Delta) E[(i+1 - i]). The inhomogeneously broadened photoluminescence (PL) peaks narrowed. The intersublevel spacings (Delta) E[(i+1 - i] were reduced and could be tuned continuously for values of (Delta) E[(i+1 - i] greater, similar and lower than the LO phonon energies in InAs and GaAs. Experiments and calculations of interdiffusion in InGaAs/GaAs quantum wells of the same ternary composition determined values for activation energies and diffusivities. These established values for diffusion lengths corresponding to the observed blue shifts and reduction of (Delta) E[i+1 - i] with annealing temperature. Rate equation simulations of our experimentally obtained PL spectra were used to estimate relaxation lifetime ratios for intersublevel transitions. A slight trend towards increasing thermalization rates at values (Delta) E[(i+1 - i] approximately LO phonon energies was found. However, PL measurements showed strong emission from excited states for all (Delta) ELB(i+1 - i] values, which ranged from 53 to 25 meV.
Modeling terahertz radiation from a photoconducting structure
Author(s):
Kate A. Remley;
Andreas Weisshaar;
Vijai K. Tripathi;
Stephen M. Goodnick
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Accurate characterization of the electromagnetic radiation arising from photoconducting systems is discussed. A computational technique is presented which combines the finite-difference time domain method with a spatial transformation, the Kirchhoff surface integral formulation. The technique enables incorporation of any number of material parameters while accurately accounting for the potentially wide-band nature of the radiation in an efficient computational method. Results are presented demonstrating a more accurate portrait of the radiation arising from a photoconducting structure than has been previously reported. Based on the simulation results, a simple model incorporating equivalent dipole sources is developed. Good agreement is shown between simulation results and measurements of similar structures.
Materials and designs for high-temperature infrared photon detectors
Author(s):
Christoph H. Grein;
R. J. Radtke;
Henry Ehrenreich
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Infrared photon detectors have significant advantages over other technologies due to their fast response times and multispectral detection capabilities. However, background- limited performance is typically not achieved without significant cooling of the detectors. We discuss several strategies from improving their high-temperature performance. They are: (1) the suppression of radiative recombination using photon recycling, (2) the suppression of both radiative and Auger recombination with carrier depletion, and (3) the suppression of Auger recombination using band structure engineering in strained layer superlattices. All three effects provide significant enhancements in detectivities. We focus on extending present-day bulk HgCdTe technology to bulk and strained layer superlattice-based HgCdTe high-temperature detectors.
InAs/Ga1-xInxSb infrared superlattice diodes: correlation between surface morphology and electrical performance
Author(s):
Frank Fuchs;
L. Buerkle;
Wilfried Pletschen;
J. Schmitz;
Martin Walther;
H. Gullich;
N. Herres;
Sabine Mueller
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The structural properties of InAs/Ga1-xInxSb infrared (IR) superlattice layers grown by MBE on GaSb substrates have been investigated using high-resolution X- ray diffraction, atomic force microscopy (AFM), secondary ion mass spectroscopy and photoluminescence (PL) spectroscopy. Excellent layers could be grown with a residual mismatch below 1 X 10-3 showing interference oscillations in the X-ray diffraction pattern and high PL efficiency. IR-photodiodes processed from such layers show high responsivity and low leakage currents. The influence of n- and p-doping on the PL efficiency of IR superlattices has been investigated, showing a stronger decrease of the PL intensity for n-doping than for p-doping. Growing the IR-SLs with an As/In V/III ratio below 5, defects with a size of about 1 to 5 micrometers in diameter are observed in the AFM scans. The surface morphology between the defects remains perfect. The defects do not significantly affect the X-ray diffraction patterns and the PL intensity. In a minority-carrier-device, such as IR- photodiodes, the defects are associated with defect-assisted tunneling currents leading to a strong degradation of the electrical performance. By optimizing the growth conditions the defect density can be significantly reduced resulting in a surface roughness given by the standard deviation of the measured height profile of the AFM measurement below 0.3 nm leading to excellent device performance.
High-speed photocurrent in quantum well infrared photodetectors
Author(s):
Harald Schneider;
Peter Koidl;
Martin Walther;
Z. Lao;
Michael Schlechtweg
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Quantum well infrared photodetectors (QWIPs) are very promising for ultrafast photodetection in the 8 - 12 micrometers infrared regime. We report on time-resolved studies of the intersubband photocurrent in GaAs/AlGaAs (QWIPs). The photocurrent is excited by sub-picosecond infrared pulses, which are obtained by difference frequency mixing of the signal and idler waves of an optical parametric oscillator. Using a particular detector geometry with < 900 micrometers 2 device area, the measured electrical pulses have a full- width at half-maximum of only 16 ps and a 10% - 90% rise time of 13 ps. For practical applications, in particular for heterodyne detection, it is desirable to reduce the noise floor by using a cooled low-noise preamplifier. We have performed experiments with a low-temperature hybrid circuit consisting of a QWIP in connection with a GaAs transimpedance amplifier based on HEMT technology. This configuration yields a rise time of 19 ps at an amplifier gain of approximately 35 dB.
Influence of interdiffusion on strained GaInSb/InAs material and its application on long-wavelength infrared photodectors
Author(s):
Alex Siew-Wan Lee;
E. Herbert Li
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Intermixing effect in type-II Ga0.6In0.4Sb/InAs superlattices is studied. The interdiffusion of both group- III and group V atoms across the heterointerface modifies the superlattices optical properties and electronic structures. The intermixed-induced strain has different effects on the band structure of the respective strained layers. Conduction band is undergone successive changes where the barrier height was initially increased in potential and subsequently became lower than the as-grown one for increasing extent of intermixing. Consequently the confinement profile is tuned from an abrupt interface to a graded shape. Intersubband transition is investigated in the intermixed superlattices where the absorption peak wavelength is red shifted continuously from the as grown 11.7 to the interdiffused 12.5 micrometers . Both the intermixed absorption and responsivity are reducing in magnitude. However, dark current is reduced at initial stage of intermixing as a result of the increase in confinement potential and the effective barrier width. Detectivity at 77 K is enhanced for the intermixed detector from 2.5 X 1011 to 3 X 1011 cm(root)Hz/W, which is comparable to the MCT detector.
Free-standing amorphous Y-Ba-Cu-O detectors for uncooled IR detection and the effects of doping
Author(s):
Mahmoud F. Almasri;
Donald P. Butler;
Zeynep Celik-Butler
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Amorphous semiconducting Y-Ba-Cu-O has shown promise as the temperature sensitive element for uncooled IR detectors as both a bolometer and pyroelectric material. Thin films can be easily fabricated by RF magnetron sputtering at room temperature from a composite target. As a bolometer, Y-Ba- Cu-O possesses a relatively high temperature coefficient of resistance of 3.5% K-1 near room temperature. As a pyroelectric detector, pyroelectric coefficients as high as 20 (mu) C/cm2-K have been measured yielding a pyroelectric figure of merit of 0.065 (cm3/J)1/2. In Y-Ba-Cu-O, the oxygen concentration has been shown to determine the hole concentration and mobility. However, the anion stoichiometry plays an equally important role in determining the electronic characteristics. In this work, we have explored the effects of substitution for Cu and the corresponding changes on the electronic properties affecting the performance as an IR detector. Further, we have fabricated micromachined 1 X 10 arrays in which utilize a self-supporting Y-Ba-Cu-O thin film geometry. In this case, the Y-Ba-Cu-O film is held above the substrate only by the electrode arms, without the need of any underlying bridge material. These detectors posses a low thermal mass and have yielded detectivities as high as 108 cm-Hz1/2/W, which extrapolates to NETDs less than 20 mK.
Characterization of optical properties of PtSi at 3.392 um from 300 K to 85 K and the relation of morphological effects
Author(s):
Shane O'Prey;
Gerald F. Cairns;
Paul Dawson
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PtSi/Si Schottky junctions, fabricated using a conventional technique of Pt deposition with a subsequent thermal anneal, are examined using X-ray diffraction, atomic force microscopy and a novel prism/gap/sample optical coupling system. With the aid of X-ray diffraction and atomic force microscopy it is shown that a post-anneal etch in aqua regia is essential for the removal of an unreacted, rough surface layer of Pt, to leave a much smoother PtSi film. The prism/gap/sample or Otto coupling ring is mounted in a small UHV chamber and has facilities for remote variation of the gap (by virtue of a piezo-actuator system) and variation of the temperature in the range of approximately 300 K - 85 K. The system is used to excite surface plasmon polaritons on the outer surface of the PtSi and thus produce sensitive optical characterization as a function of temperature. This is performed in order to yield an understanding of the temperature dependence of phonon and interface scattering of carriers in the PtSi.
Self-cleaning effect and compensation mechanisms in Cl-doped high-resistivity cadmium telluride
Author(s):
Vladimir N. Babentsov;
Victoria Corregidor;
Klaus-Werner Benz;
Tobias Feltgen;
Michael Fiederle;
Ernesto Dieguez
Show Abstract
In this report a new up to dated view on the compensation mechanism in CdTe bulk crystals doped with Cl in concentration up to 1019 cm-3 is given. This concentration of Cl doping gives a high resistivity material. The chlorine atoms can act as shallow donors being in Te sites or can form complex with cadmium vacancies, so called A-centers. Spatially resolved EDAX mapping of CdTe doped revealed nonstoichiometrical areas distributed over the surface. In these areas there are a high concentration of impurities, where the Cl is located in a very small inclusions, while Na is distributed all over the volume of the big inclusions. After a short-time annealing (4 hours) at low temperature (500 degree(s)C) in Cd atmosphere the areas with deviation from stoichiometry mostly disappeared as well as the inclusions which were present inside. This paper includes a review of the different aspects, which can influence a precise compensation mechanism in a non-doped and Cl doped CdTe.
Structure and physical properties of Zn1-xMgxSe single crystals
Author(s):
Yuri A. Zagoruiko;
O. A. Fedorenko;
N. O. Kovalenko;
M. A. Rom;
O. N. Chugai;
P. V. Mateichenko
Show Abstract
The vertical Bridgman method is used to obtain crystals of Zn1-xMgxSe solid solutions (0.03
Noise characteristics of bootstrapped photovoltaic and photoconductive detectors
Author(s):
Janos P. Makai;
Jozef J. Makai;
Janos Balazs
Show Abstract
If linearity of a semiconductor photodetector is a critical issue in an application like in radiometry, spectrophotometry, etc. the detectors are used in the so called current measurement mode. In this mode the detector is directly connected to a current-to-voltage converter, consequently in an ideal situation all the photogenerated charge carriers appear on the feedback resistor of the converter and produce a voltage drop. Photovoltaic detectors are short circuited by the converter, the built in electric field of the detector transfers the generated carriers to the converter. On the other hand photoconductive detectors should be biased externally by a constant voltage to produce an internal field for the transport of the charge carriers. Some applications need great area detectors, that especially in the IR wavelength region show low shunt resistance values. Ge, InAs, InSb, PbS, PbSe, HgCdTe, etc., have many decades lower shunt resistance values than that of a Si or InGaAs detector operating in the visible or near infrared region. If high sensitivity is needed than a high value of the feedback resistor is required that decreases the closed loop gain, consequently the settling accuracy. Bootstrapping of the detectors virtually increases the shunt resistance and so restores the decreased closed loop gain and settling accuracy. The bootstrapping technique will be shown and the noise characteristics will be analyzed and compared to the traditional solutions.
MOSES: a modular sensor electronics system for space science and commercial applications
Author(s):
Harald Michaelis;
Thomas Behnke;
Matthias Tschentscher;
Stefano Mottola;
Gerhard Neukum
Show Abstract
The camera group of the DLR--Institute of Space Sensor Technology and Planetary Exploration is developing imaging instruments for scientific and space applications. One example is the ROLIS imaging system of the ESA scientific space mission `Rosetta', which consists of a descent/downlooking and a close-up imager. Both are parts of the Rosetta-Lander payload and will operate in the extreme environment of a cometary nucleus. The Rosetta Lander Imaging System (ROLIS) will introduce a new concept for the sensor electronics, which is referred to as MOSES (Modula Sensor Electronics System). MOSES is a 3D miniaturized CCD- sensor-electronics which is based on single modules. Each of the modules has some flexibility and enables a simple adaptation to specific application requirements. MOSES is mainly designed for space applications where high performance and high reliability are required. This concept, however, can also be used in other science or commercial applications. This paper describes the concept of MOSES, its characteristics, performance and applications.
High-performance 480x12x4 linear CMOS IR multiplexer
Author(s):
Charles F. Walmsley;
Timothy R. Beystrum;
Charles Glasser;
Ray Himoto;
Mark K. Preis;
Dave Parkinson
Show Abstract
This paper describes a linear CMOS IR multiplexer comprising four spectral bands, each with 480 channels of 12 TDI elements. The multiplexer is designed to interface with high R0A InSb detectors manufactured by Litton EOS, Tempe, AZ. The requirement to handle a wide range of photocurrents down to 100 fA, yet maintaining a signal bandwidth in excess of 2.5 kHz imposed significant demands on the input buffer amplifier design. In addition, each detector cell incorporates a sample/hold stage to allow snapshot operation mode. These features lead to a challenging layout for the 32 micrometers pitch to be met. To optimize dynamic range, each band may be independently operated with one of three gain settings set by switchable capacitors within the unit cell. Other architectural features of the array include bi- directional scanning, externally controllable integration time and electrical test. The array dissipates less than 50 mW of power and exhibits less than 65 noise electrons at high gain setting. A 0.7 micrometers silicon technology was used. Special design techniques were employed to allow operation at 7.5 V, thereby enhancing dynamic range. IR cameras incorporating the multiplexer are currently being delivered to the customer.
Various layouts of analog CMOS optical position-sensitive detectors
Author(s):
Davies W. de Lima Monteiro;
Gleb V. Vdovin;
Pasqualina M. Sarro
Show Abstract
We report on the fabrication and characterization of analog multi-pixel optical position-sensitive detectors (PSDs) for sensing the 2D position of a light spot over the sensor area. Computer simulations were performed to understand the influence of the geometrical layout of the device on the linearity of response. Standard CMOS technology was chosen for fabrication so that the detectors are compatible with reliable low-cost and low-power electronics for integration with processing electronics. Three chessboard-like 5 X 5- pixel structures, with different pixel layouts have been implemented. The response linearity was calculated and measured over 80% of the detector active area. It was shown that chessboard-like structures are not suitable for spot diameters below 2 pixels. For a light spot diameter comparable with the device size, the best linearity of response--RMS deviation of less than 4%--among all three structures is achieved by the structure with vertical phototransistors as the photo-sensing elements. We also implemented a PSD with two complementary spiral structures, providing sensing for both coordinates in each pixel. With this layout we achieved RMS non-linearity of less than 3.5% for a spot size comparable with pixel size in close agreement to the simulations. The computer model indicates that the non-linearity for all structures studied decreases with the number of pixels.
Avalanche photodiode array sensor with high-speed CCD delay line readout
Author(s):
Kevin L. Albright;
Jeffrey M. Bradley
Show Abstract
A prototype solid-state multi-chip-module (MCM) optical sensor circuit is described. The MCM is designed to sample the optical signals from a fiber-optic array at rates up to 200 MHz. The fiber-optic inputs interface to the MCM avalanche-photodiode (APD) sensor array. The prototype 40 pixel MCM stores approximately 1000 samples from each fiber before readout. This is done on the MCM using high-speed charge-injection input CCD delay line ICs. The MCM is designed to be cooled to 0 degrees C. This stabilizes the APD gain and minimizes dark current generation in the APD and the CCD delay line.
High-speed backside-illuminated time-delay-integration (TDI) CCDs
Author(s):
John R. Tower;
Thomas M. Sudol;
Vipulkumar Patel;
Pradyumna K. Swain;
Peter A. Levine;
Fu-Lung Hsueh;
Robin M. Dawson;
Grazyna M. Meray;
James T. Andrews;
S. Goldfarb
Show Abstract
A backside illuminated time delay integration (TDI) charge coupled device (CCD) technology has been developed. Imagers have been demonstrated at 13 pm pixel size and 8 pm pixel size. Photocomposition (stitching) has been employed to realize TDI iinagers of length < 60 mm. Performance has been enhanced in the areas of quantum efficiency, dynamic range, modulation transfer function (MTF), and line scan rates. The focus of this work has been to develop this new generation of line scan imagers for advanced reconnaissance applications. The enhancements permit the deployment of new camera systems with higher sensitivity, and higher resolution. To support the deployment of this technology into rugged environments, a custom packaging technology has been 'developed. The packages provide a hermetic enclosure for the CCD and establish precise alignment of the CCD pixels to the package mounting fixture. This paper will summarize the design features of the 13 pm pixel and 8 jim pixel TDI arrays. Measured performance will be presented. Future plans for this backside illuminated TDI technology will be discussed.
Ultrahigh-resolution 14,400-pixel trilinear color image sensor
Author(s):
Thomas Carducci;
Antonio S. Ciccarelli;
Brent J. Kecskemety
Show Abstract
An ultra-high resolution 14,400 pixel trilinear image sensor is under development to meet customer requirements as they progress into next generation, high-end color scanning systems. High-performance features being incorporated into this device include an enhanced color filter scheme providing improved blue and green responsivity, electronic exposure control, and antiblooming protection. To our knowledge, this will be the highest resolution trilinear sensor to date and is being designed to provide common optical length to Kodak's current line of long trilinear imagers.
