This PDF file contains the front matter associated with SPIE Proceedings Volume 8626, including the Title Page, Copyright Information, Table of Contents, and the Conference Committee listing.

The dependences of the 294-K and 10-K mobility μ and volume carrier concentration n on thickness (d = 25 – 147 nm) were examined in Al-doped ZnO (AZO) layers grown in Ar ambient at 200 °C on quartz-glass substrates. Two AZO layers were grown at each thickness, one with and one without a 20-nm-thick ZnON buffer layer grown at 300 °C in Ar/N₂ ambient. Plots of the 10-K sheet concentration n_s vs d for buffered (B) and unbuffered (UB) samples give straight lines of similar slope, n = 8.36 x 10²⁰ and 8.32 x 10²⁰ cm^-3, but different x-axis intercepts, δd = -4 and +13 nm, respectively. Thus, the electrical thicknesses are d - δd = d + 4 and d - 13 nm, respectively. Plots of n_s vs d at 294 K produced substantially the same results. Plots of μ vs d can be well fitted with the equation μ(d) = μ(infinity symbol)/[1 + d*/(d-δd)], where d* is the thickness for which μ(infinity symbol) is reduced by a factor 2. For the B and UB samples, d* = 7 and 23 nm, respectively, showing the efficacy of the ZnON buffer. Finally, from n and μ(infinity symbol) we can use degenerate electron scattering theory to calculate bulk donor and acceptor concentrations of 1.23 x 10²¹ cm^-3 and 1.95 x 10²⁰ cm^-3, respectively, and Drude theory to predict a plasmonic resonance at1.34 μm. The latter is confirmed by reflectance measurements.

Due to their combination of good electrical conductivity and optical transparency, Transparent Conducting Oxides (TCOs) are the most common choice as transparent electrodes for optoelectronics applications. In particular, devices, such as LEDs, LCDs, touch screens and solar cells typically employ indium tin oxide. However, indium has some significant drawbacks, including toxicity issues (which are hampering manufacturing), an increasing rarefication (due to a combination of relative scarcity and increasing demand [1]) and resulting price increases. Moreover, there is no satisfactory option at the moment for use as a p-type transparent contact. Thus alternative materials solutions are actively being sought. This review will compare the performance and perspectives of graphene with respect to TCOs for use in transparent conductor applications.

In order to facilitate the development of next-generation display devices or modern solar cells, material performance is critically important. A combination of high transparency in the optical spectral range and high electrical conductivity under ambient conditions is attractive, if not crucial, for many applications. While the doping-induced presence of free electrons in the conduction bands of CdO can increase the conductivity up to values desired for technological applications, it is, however, expected to impact the optical properties at the same time. More specifically, variations of the band gap, effective electron mass, and optical-absorption onset have been reported. In this work recent results from modern theoretical spectroscopy techniques are compared to experimental values for the optical band gap in order to discuss the different effects that are relevant for an accurate understanding of the absorption edge in the presence of free electrons with different concentrations.

Plasmonics combines attractive features of nanoelectronics and optics enabling highly integrated, dense subwavelength optical components and electronic circuits which will help alleviate the speed-bottleneck in important technologies such as information processing and computing. The wide application of plasmonic devices hinges on practical demonstrations with low losses at standard optical wavelengths such as near infrared, visible, telecom, etc. Conventional plasmonic devices, based on noble metals, suffer from large losses in these frequency regimes and are difficult to compensate completely by simply adding gain material. Transparent conducting oxides (TCOs) such as ZnO are good alternatives to metals for plasmonic applications in the optical regime since they exhibit high conductivity and relatively small negative real permittivity values necessary for practical plasmonic devices. Ga-doped ZnO layers were grown on Al₂O₃ at 200 °C by pulsed laser deposition in Ar ambient. The electrical properties, determined by the Hall effect, were: ρ = 2.95x 10^-4 Ω-cm; μ = 25.3 cm²/V-s; and n = 8.36 x 10²⁰ cm^-3. These values of μ and n were used to predict optical properties through the Drude dielectric function. Reflection measurements confirmed the Hall-effect predictions. The optical and electrical properties of the material were used to design insulator-metal-insulator (in our case, Quartz-ZnO-polymer) waveguides for long range plasmons using full-wave electromagnetic models built with finite element method simulations. The models were used to predict the behavior of ZnO as well as examine the effect of device geometry on propagation length and losses of the plasmon mode.

X-ray photoelectron spectroscopy (XPS) is used to compare the composition as a function of depth of as-grown ZnO films heavily doped with Ga and similar samples annealed in air for 10 min. at 600 °C, with particular attention given to the near-surface region. These films were grown by pulsed laser deposition (PLD) using a ZnO target containing 3 wt% Ga₂O₃. The electrical properties of these samples were determined from temperature-dependent Hall-effect measurements. The as-grown film has the following characteristics: i) a ~1:1 Zn:O ratio with a Ga concentration of ~ 3.3 atomic percent; ii) no excess Ga in the near-surface region; and iii) excellent electrical characteristics: ρ=2.42×10^-4 Ω-cm, n=8.05×10²⁰ cm^-3, and μ=32.1 cm²/V-s at 300 K. For the annealed sample: i) the Zn:O ratio remains ~ 1:1, but the Ga concentration is ~ 3 atomic percent which is ~10% lower than in the as-grown film; ii) ~7 at% Ga is measured in the near-surface region; and iii) a significant increase in resistivity to ρ = 0.99 Ω-cm, n = 1.97×10¹⁸ cm^-3, and μ=3.2 cm²/V-s at 300 K. Analysis of the O chemical shift suggests formation of a mixed ZnO/Ga₂O₃ surface layer ≤ 5 nm thick accounts for the observed changes in the Ga profile after annealing.

Wide band gap oxide media including 4fⁿ or 3dⁿ ions attracts a considerable attention in the context of photonics and bio-photonics applications due to the electromagnetic widespread spectral range covered by the intraionic radiative relaxation of the charged lanthanide and transition metal ions. Converting ultraviolet commercial light into visible luminescence continues to raise interest for the solid state light market, justifying the demand for new and efficient phosphors with wide spectrum coverage and improved thermal quenching behavior. New materials and methods have been thoroughly investigated for the desired purposes. In this work, we report on laser processing for the growth of oxides media such as ZrO₂, ZnO among other oxide hosts. The transparent crystalline materials in-situ doped with different amounts of lanthanide or transition metal ions are explored in order to enhance the room temperature ions luminescence by pumping the samples with ultraviolet photons. Spectroscopic studies of the undoped and doped oxide hosts were performed using Raman spectroscopy, photoluminescence (PL) and photoluminescence excitation (PLE).

Plasma Profiling Techniques provide direct measurement of the chemical composition of materials as a function of depth, with nanometre resolution and the capability to measure both thin and thick layers. These techniques rely on the fast sputtering of a representative area of the material of interest by a high density (10¹⁴/cm³) and low energy plasma. The unique characteristics of this plasma allow very fast erosion (2 - 10 nm/s) with minimum surface damage (as the incident particles have an average energy of about 50 eV) which has been shown to be advantageous for SEM sample preparation. When coupled to a high resolution optical system, the resulting technique is called RF GD-OES and is well established, when coupled to TOFMS detection, it is named Plasma Profiling Time of Flight Mass Spectrometry, a newly commercialized variation of the same technique. Both instruments feature an advanced pulsed RF source allowing the measurements of conductive and non conductive layers. Various applications will be presented ranging from thin film analysis for composition, contamination detection, surface area measurements and doping level to characterization of diffusion mechanisms. Aspects of analytical performance with regards to sensitivity, quantification, repeatability and sample throughput will be discussed.

Bulk ZnO crystals were grown by the hydrothermal technique with Al₂O₃ added to the solution in an attempt to obtain Al-doped ZnO crystals. Aluminum and indium co-doped ZnO were also grown by the same technique. Adding Al₂O₃ to the growth solution has a significant impact on the ZnO growth ⎯ either preventing overgrowth and dissolving the seed growth or degrading the crystalline quality; nevertheless, the resulting crystals of both Al:ZnO and Al/In:ZnO are highly conductive, similar to In and Ga doped ZnO crystals, with a resistivity approaching 0.01 Ω cm, as revealed by temperature-dependent Hall-effect measurements. Photoluminescence spectra at 18 K show Al⁰-bound-exciton peak energies of 3.3604 eV on the Zn face and 3.3609 eV on the O face for the Al-doped ZnO crystals. Similarly both an Al⁰- bound-exciton peak at 3.3604 eV and an In⁰-bound-exciton peak at 3.3575 eV were found on the Al/In-co-doped crystals. The electrical properties of all group III doped ZnO crystals grown hydrothermally are compared with each other and with Al:ZnO obtained by other growth methods.

Owing to its wide bandgap (3.37eV) and a large exciton binding energy (60meV), fabrication of ZnO based optoelectroincs devices is a very active research area. Hence, enhancing the photoluminescence of the ZnO films will be important to achieve higher efficiency optoelectronic devices. Hydrogen ion implantation (Energy = 50keV, Dose = 5×10¹²cm^-2) have been performed on Pulsed Laser Deposited ZnO thin films deposited at 650°C. The samples were subsequently subjected to Rapid Thermal Annealing at 750°C, 800, 850°C and 900°C for 30 seconds in oxygen environment. X-ray Diffraction study confirms deposition of highly oriented <002> ZnO films for all the samples. However, the peaks for the samples are not at the same position due to the strain induced during implantation and subsequent annealing. Low temperature photoluminescence (8K) spectra of the samples revealed the presence of peaks of donor-bound exciton (D°X) and free-exciton (FX) at 3.36eV and 3.37eV respectively. Deep level defect peak around 2.5eV was also observed in the samples but the intensity of these peaks was substantially weaker than the near band edge (NBE) peaks verifying the high quality of the films. Moreover, the integrated PL peak intensity of the NBE show that the luminescence gets considerably enhanced as the samples are implanted (4 times) and subsequently annealed (up to 100 times) when compared with the as-deposited sample. Thus, implanting hydrogen ions maybe a good way to enhance the photoluminescence and thus efficiency for ZnO based devices.

Zinc oxide (ZnO) is a biocompatible and versatile functional material having a bandgap of 3.37 eV that exhibits both semiconducting and piezoelectric properties and has a diverse group of growth morphologies. We have grown highly ordered vertical arrays of ZnO nanowires (NWs) using a metal organic chemical vapor deposition (MOCVD) growth process on various substrates. The NWs were grown on p-Si (100), SiO₂, and m-plane sapphire substrates. The structural and optical properties of the grown vertically aligned ZnO NW arrays were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and photoluminescence (PL) measurements. The unique diffraction pattern for ZnO (002) concurred with the SEM inspection indicating vertical orientation of the NWs. UV detectors based on ZnO NWs offer high UV sensitivity and low visible sensitivity for applications such as missile plume detection and threat warning. Compared to the photomultiplier tubes (PMTs) prevalent in current missile warning systems, the NW detector arrays are expected to exhibit low noise, extended lifetimes, and low power requirements for UV detector applications.

Single crystal β-Ga₂O₃ epitaxial layers have been prepared on c-axis (0001) sapphire substrates using metalorganic chemical vapor deposition technique at relatively low temperature. Post-annealing of β-Ga₂O₃ single crystals up to 800 °C does not affect the crystallinity, explored by x-ray diffraction, showing that β-Ga₂O₃ epitaxial layers are highly (-201) oriented. Metal-semiconductor-metal devices are fabricated on single crystals to study their photoresponsivity. A significant improvement in performance of post annealed-based devices is observed, attributed to point defect reduction. Annealing of as-grown samples results to a significant decrease in both oxygen and gallium vacancies, which are sources of current leakage.

Heterostructures and superlattices consisting of a prototype Mott insulator, GdTiO₃, and the band insulator SrTiO₃, are grown by molecular beam epitaxy and show intrinsic electronic reconstruction, approximately ½ electron per surface unit cell at each GdTiO₃/SrTiO₃ interface. Insights into charge distribution, the influence of the electrostatic boundary conditions, and strong correlation effects will be presented.

Indium Gallium Nitride (InGaN) based PV have the best fit to the solar spectrum of any alloy system and emerging LED lighting based on InGaN technology and has the potential to reduce energy consumption by nearly one half while enabling significant carbon emission reduction. However, getting the maximum benefit from GaN diode -based PV and LEDs will require wide-scale adoption. A key bottleneck for this is the device cost, which is currently dominated by the substrate (i.e. sapphire) and the epitaxy (i.e. GaN). This work investigates two schemes for reducing such costs. First, we investigated the integration of Zinc Oxide (ZnO) in InGaN-based diodes. (Successful growth of GaN on ZnO template layers (on sapphire) was illustrated. These templates can then be used as sacrificial release layers for chemical lift-off. Such an approach provides an alternative to laser lift-off for the transfer of GaN to substrates with a superior cost-performance profile, plus an added advantage of reclaiming the expensive single-crystal sapphire. It was also illustrated that substitution of low temperature n-type ZnO for n-GaN layers can combat indium leakage from InGaN quantum well active layers in inverted p-n junction structures. The ZnO overlayers can also double as transparent contacts with a nanostructured surface which enhances light in/out coupling. Thus ZnO was confirmed to be an effective GaN substitute which offers added flexibility in device design and can be used in order to simultaneously reduce the epitaxial cost and boost the device performance. Second, we investigated the use of GaN templates on patterned Silicon (100) substrates for reduced substrate cost LED applications. Controlled local metal organic chemical vapor deposition epitaxy of cubic phase GaN with on-axis Si(100) substrates was illustrated. Scanning electron microscopy and transmission electron microscopy techniques were used to investigate uniformity and examine the defect structure in the GaN. Our results suggest that groove structures are very promising for controlled local epitaxy of cubic phase GaN. Overall, it is concluded that there are significant opportunities for cost reduction in novel hybrid diodes based on ZnO-InGaN-Si hybridization.

The origin of a double peak, detected by X-ray diffraction (XRD), in a wurtzite Cd_xZn_1-xO (x=0.17) epilayer, is investigated using Rutherford backscattering spectrometry in channeling geometry (RBS/C). In-depth compositional characterization by RBS/C demonstrates that strain relaxation does not take place via compositional phase separation and does not cause any compositional pulling effects. On the contrary, RBS/C angular scans demonstrate that relaxation is a consequence of progressive structural changes during the heteroepitaxial growth of the film on MgZnO, likely due to the large distortion of the lattice induced by the high Cd content.

We will present some of our results from low temperature (<100 °C) chemical growth of inorganic zinc oxide (ZnO) crystalline nanostructures on non-conventional substrates. These non-conventional substrates include plastic, paper, and textile fabrics. Both nanowires and nanotubes are grown at low temperature. The nanowires were processed to fabricate white light emitting diodes (LEDs) with color rendering index (CRI) of up to 95. Then both the nanowires and nanotubes were tested regarding the piezoelectric effect and for generating electric power from mechanical movements. This opens the possibility to drive the LEDs from harvesting ambient mechanical movements. We also developed a printing process suitable for mass production to fabricate these LEDs on paper substrates. Also on the paper contacts and interconnection lines were made by a simple pencil drawing on the paper on which the nanowires then were printed. This ZnO nanocrystals graphitic circuitry worked excellent as metal electrodes. In this way a UV-detector was fabricated. Finally, we will also compare the paper substrates results with our other results on other different types of flexible substrates like cotton and plastic substrates.

Last generation medical imaging equipments require materials which possess outstanding performances. For scintillators in the high energy imaging field (PET), crystals with high light yields allow a decrease of the irradiation dose received by the patients during medical application and a more accurate diagnostic. Thermally stimulated luminescence (TSL) data provides the depth of hole or electron traps which can limit the efficiency and increase the kinetic. If these traps are due to lanthanide ions, the level schemes can predict the depth values. Thanks to comparison between TSL glow curves and energy diagrams, the traps inside oxide-based-hosts can be identified. Two examples are proposed here, first, the scintillation in the Ce:LYSO crystals which can be improved by thermal annealing and where divalent cations are used for charge compensation and traps removal and second, optical imaging using a new approach where persistent luminescent nanoparticles are used for in-vivo imaging. In both cases, traps depth should be carefully controlled.

TiO₂ is well known as a low-cost, highly active photocatalyst showing good environmental compatibility. Recently it was found that TiO₂ nanotubes promise to enable for high photocatalytic activity (PCA). In our experiments, we studied the PCA and spectroscopic properties of TiO₂ nanotube arrays formed by the anodization of Ti. The PCA efficiency related to the decomposition of methylene-blue was measured. To obtain reliable data, the results were calibrated by comparing with standard materials like Pilkington Activ™ which is a commercially available self cleaning glass. The studies included a search strategy for finding optimum conditions for the nanotube formation and the investigation of the relationship between PCA and annealing temperature. TiO₂ nanotubes of different shapes and sizes were prepared by an anodization of Ti foil in different electrolytes, at variable applied voltages and concentrations. The photo-dissociation of methylene-blue was detected spectroscopically. For the optimized material, an enhancement factor of 2 in comparison to the standard reference material was found. Furthermore, femtosecond-laser induced photoluminescence and nonlinear absorption of the material were investigated. Possibilities for further enhancements of the PCA are discussed.

Interest on the control of light at the nano- and microscale has increased in the last years because of the incorporation of nanostructures into optical devices. In particular, semiconductor oxides microstructures emerge as important active materials for waveguiding and confinement of light from UV to NIR wavelengths. The fabrication of high quality and quantity of nano- and microstructures of semiconductor oxides with controllable morphology and tunable optical properties is an attractive challenge in this field. In this work, waveguiding and optical confinement applications of different micro- and nanostructures of gallium oxide and antimony oxide have been investigated. Structures with morphologies such as nanowires, nanorods or branched nanowires as elongated structures, but also triangles, microplates or pyramids have been obtained by a thermal evaporation method. Light waveguide experiments were performed with both oxides, which have wide band gap and a rather high refractive index. The synthesized microstructures have been found to act as optical cavities and resonant modes were observed. In particular, photoluminescence results showed the presence of resonant peaks in the PL spectra of Ga₂O₃ microwires and Sb₂O₃ micro-triangles and rods, which suggest their applications as optical resonators in the visible range.

Zinc oxide (ZnO) has attracted considerable attension due to its wide applications in particular ultra violet light emitting diode (UV-LED). In addition, the one-dimensional ZnO crystals are quite attractive as building blocks for light emitting devices like laser and LED, because of their high crystallinity and light confinement properties. However, a method for the realization of the stable p-type ZnO has not been well established. In our study, we have investigated the effect of the nanosecond laser irradiation to the ZnO nanorods as an ultrafast melting and recrystallizing process for realization of the p-type ZnO. Fabrication of the p-n homo junction along ZnO nanorods has been demonstrated using phosphorus ion implantation and ns-laser annealing by a KrF excimer laser. Rectifying I-V characteristics attributed to p-n junction were observed from the measurement of electrical properties. In addition, the penetration depth of laser annealed layer was measured by observing cathode luminescence images. Then, it was turned out that high repetition rate laser annealing can anneal ZnO nanorods over the optical-absorption length. In this report, optical, structural, and electrical characteristics of the phosphorus ion-implanted ZnO nanorods annealed by the KrF excimer laser are discussed.

Zinc oxide (ZnO) has a wide band-gap energy of 3.37 eV and a large exciton binding energy of 60 meV which is considerably larger than the thermal energy at room temperature (26 meV), and therefore, efficient exciton emission in ultraviolet (UV) region can be expected. Especially, ZnO micro/nanocrystals are quite attractive as building blocks for efficient UV opto-electronic devices. We have been investigating micro-cavity UV lasing from variously-shaped ZnO micro/nanocrystals, and micro-cavity lasing from ZnO nanowire and nanosheet have been confirmed, so far. Recently, we could fabricate ZnO micro/nanosphere crystals by a simple laser ablation method of ZnO sintered target in the air. In this study, we report UV micro-cavity lasing from an optically-pumped single ZnO micro/nanosphere crystal, for the first time. The spherical-micro-cavity lasing characteristics were investigated and discussed by comparisons with theoretical considerations in terms of quality factor and mode spacing of its lasing spectra with modal structures. From those considerations, it was found that the lasing mechanisms within a ZnO sphere crystal was attributed to whispering-gallery- mode (WGM) cavity lasing, and a ZnO sphere crystal had a good light confinement property due to the internal total reflections. Since the fabrication method is very simple and productive without any time-consuming crystal-growth process, ZnO micro/nanosphere crystals can be promising building blocks for UV opto-electronic devices such as a UV laser diode. In addition, since a ZnO micro/nanosphere can operate as an active WGM refractometric sensor for small molecules in UV region, high sensitivity enhanced by high quality factor, refractive index, and wavelength dispersion can be expected.

ZnO as a wide band gap semiconductor is of significant interest for various applications, including dye-sensitized solar cell (DSSC) and photocatalytic degradation of organic pollutants. For DSSC, although the performance of ZnO-based devices is generally inferior to TiO₂-based ones, it is still of interest due to its high electron mobility. While the relationship between the material and the device performance are complicated, many studies have been focused on morphologies and surface area of the nanomaterials. The studies of the effect of the material properties such as the types and concentrations of native defects on the DSSC performance have been scarce. For photocatalytic degradation of pollutants, many reports showed ZnO has a higher or similar efficiency compared to the commonly used TiO₂. Reports have also pointed out the important role of native defects of ZnO in its photocatalytic activity. Nevertheless, the effect of the type and location of the defects has been contradictory in the literature indicating that there is a complex relationship. Therefore, we will discuss the effect of ZnO native defects on the dye adsorption, charge transport and hence the DSSC performance. We will also discuss their influence on reactive oxygen species (ROS) generation and photocatalytic dye degradation. As photoluminescence (PL) is a common methodology in studying native defects of ZnO, the relationship between PL, DSSC performance and photocatalytic properties will also be investigated. Preliminary results showed a higher overall PL intensity would result in a better device performance and higher photocatalytic activities.

TCO films are crucial components of almost all thin-film solar cells and a-Si:H/c-Si heterojunction solar cells. As they are used as front contacts, the requirements for electrical conductivity and optical trnamission are generally very high. Further restrictions are imposed onto the deposition process by the cell manufacturing process, in which e.g. the maximum substrate temperature can be limited. In this paper the optimization of ZnO:Al layer deposited by magnetron sputtering to different solar cells is discussed. For a-Si:H/c-Si heterojunction solar cells the advantages and limitations of different variations of magnetron sputtering of ZnO:Al are discussed and compared to standard ITO deposition. For a-Si:H/μc-Si:H the usage of post-deposition treatments to improve the optical and electrical performance is briefly discussed.

We have investigated a large variety of ZnO structures prepared by sol-gel, electrodeposition and occlusion electrolysis for dye-sensitized solar cell (DSSC) application. The micro-/nanostructures include (nano)porous films, nanowire arrays and hierarchical structures. Several dyes (D149, D205, N719, Z907) have been tested. We have found that the best system is the nanoporous ZnO film prepared by electrodeposition using EY as a structure directing agent and sensitized by the D149 indoline dye in the presence of octanoic acid. Electrochemical impedance spectroscopy (EIS) investigation of the cells’ functioning shows a high charge collection efficiency of the ZnO-based photoelectrodes (>92%). Combined with IPCE measurements, we conclude to a high charge injection efficiency (>95%). However, the cell optimizing must now focus on the light harvesting efficiency that must be increased by broadening the sunlight wavelength range collected at the ZnO-based photoelectrode.

InGaN-based p-i-n structures were transferred from sapphire to soda-lime glass substrates using two approaches: (1) laser-lift-off (LLO) and thermo-metallic bonding and (2) chemical lift-off (LLO) by means sacrificial ZnO templates and direct wafer bonding. Both processes were found to function at RT and allow reclaim of the expensive single crystal substrate. Both approaches have also already been demonstrated to work for the wafer-scale transfer of III/V semiconductors. Compared with the industry-standard LLO, the CLO offers the added advantages of a lattice match to InGaN with higher indium contents, no need for an interfacial adhesive layer (which facilitates electrical, optical and thermal coupling), no damaged/contaminated GaN surface layer, simplified sapphire reclaim (GaN residue after LLO may complicate reclaim) and cost savings linked to elimination of the expensive LLO process.

Epitaxial LiNbO₃ thin films were deposited on C-sapphire substrates by pulsed injection metal organic chemical vapor deposition and atmospheric pressure metal organic chemical vapor deposition. The effect of deposition conditions, such as the ratio of Li/Nb precursors in solution and the deposition pressure, on the phase composition, Li nonstoichiometry, texture, epitaxial quality, residual stresses and formation of twins in LiNbO₃ films was studied by means of X-ray diffraction and Raman spectroscopy. It was found that the deposition pressure played an important role in the incorporation of Li₂O in the film and the formation of in-plane and out-of-plane twins.

Nanothermochromic diffraction gratings based on the metal-insulator transition of VO₂ are fabricated by site- selective ion-beam implantation in a SiO₂ matrix. The studied diffraction gratings were defined (i) directly by spatially selective ion-beam synthesis or (ii) by site-selective deactivation of the metal-insulator transition by ion-beam induced structural defects. The strongest increase of the diffraction efficient was observed at a wavelength of 1550 nm exceeding one order of magnitude for the selectively deactivated gratings. The observed pronounced thermal hysteresis extends down close to room temperature and makes these optical elements well suited for optical memory devices.

In this work the performance of bottom gate thin film transistors (TFTs) with transparent amorphous gallium tin zinc oxide (GSZO) active layers fabricated by radio frequency sputter deposition using a single GSZO target on SiO₂/Si wafers will be presented. Trap density and its energetic distribution, and oxygen chemisorption were found to play a critical role in determining the operational characteristics of the device, all of which can be controlled by the oxygen incorporation and substrate temperature during deposition, along with the post-deposition annealing. In addition device instability, with respect to the electrical stress and optical illumination, can be suppressed by suitably tailoring these parameters. TFTs exhibiting a drain current (I_D) of 10^-6 A and on/off current ratio (I_on/off ) of 10⁶ was achieved. A stable TFT has been achieved under electrical stress for 2% oxygen flow exhibiting ΔV_T as low as ~0.5 V for 3hr stress under a gate bias of 1.2 and 12 V, with good optical stability.

In this study, TiO₂ films were deposited using thermal Atomic Layer Deposition (ALD) system. It is observed that asdeposited ALD TiO₂ films are amorphous and not suitable as TFT channel material. In order to use the film as channel material, a post-annealing process is needed. Annealed films transform into a polycrystalline form containing mixed anatase and rutile phases. For this purpose, devices are annealed at 475°C and observed that their threshold voltage value is 6.5^V, subthreshold slope is 0.35 V/dec, I_on/I_off ratios 2.5×106 and mobility value is 0.672 cm²/V.s. Optical response measurements showed that devices exhibits decent performance at ultraviolet region where TiO₂ has band to band absorption mechanism.

Here, two Praseodymium doped ZnO multilayer varistor (MLV) samples with Ag/Pd electrodes were macroscopically and microscopically investigated. Since the varistor effect is a grain boundary effect, the electrical properties of individual ZnO grain boundaries were especial subject of this study. Both samples were cross sectioned for the AFM based investigation. Besides conductive atomic force microscopy (C-AFM), Kelvin Probe Force Microscopy (KPFM) and KPFM with a voltage applied between the varistor electrodes, so called scanning surface potential microscopy (SSPM), have been employed. Both samples were mapped with electron backscatter diffraction (EBSD) after the AFM based investigations. In C-AFM, a high conductivity of the ZnO grains and a high resistivity of the grain boundaries was proven. With SSPM, individual grain boundaries with an asymmetric electrical behavior were identified. These grain boundaries are causing asymmetric current paths and therefore can cause asymmetric device behavior.

In this work we report the influence of the crystallization stage of the host matrix on the spectroscopic properties of rare earth ions in CaSiO₃/Ca₃(PO₄)₂ biocompatible eutectic glass-ceramics grown by the laser floating zone technique. The microstructural analysis shows that either a growth rate increase or a rod diameter decrease leads the system to a structural arrangement from three (two crystalline and one amorphous) to two phases (one crystalline and one amorphous). The crystalline phases correspond to apatite-like and Ca₂SiO₄ structures. Site-selective laser spectroscopy allows to distinguish between crystalline and amorphous environments for the Nd³⁺ ions and to correlate the spectroscopic properties with the microstructure of these eutectics.

Highly (-201) oriented β-Ga₂O₃ films prepared by metal-organic chemical vapor deposition on (0001) sapphire substrates, undergone different post annealing temperatures to study their resistivity under harsh environment. Both of Rutherford backscattering spectrometry and cross-sectional transmission electron microscopy (TEM) results are exposing a harmony between oxygen vacancies and gallium interstitials. TEM characterization of samples determines a relationship between interstitials and formation of screw dislocations. Cathodoluminecsnece investigated under different applied voltages is found to be applicable to study chemistry of the bulk and surface of β-Ga₂O₃.

Titanium dioxide (TiO₂) has several attractive properties such as high linear and nonlinear refractive indices and the wide bandgap for applying the nonlinear optical devices. We have been studied channel waveguides with TiO₂ as the submicron size core to verify their feasibility as the nonlinear optical devices. In this study, we analyzed optical propagation in the TiO₂ photonic crystal waveguide and demonstrated the enhanced optical nonlinearity due to slow light effect.

Polycrystalline anatase-TiO₂ thin film possesses desirable properties for on-chip photonic devices that can be used for optic computing, communication, and sensing. Low-loss anatase-TiO₂ thin films are necessary for fabricating high quality optical devices. We studied anatase-TiO₂ by reactively sputtering titanium metal in an oxygen environment and annealing. By correlating key deposition parameters, including oxygen flow rate, deposition pressure, RF power, and temperature to film morphology and planar waveguiding losses, we aim to understand the dominant source of propagation losses in TiO₂ thin films and achieve higher quality, lower-loss films.

Heavy metal oxide glasses exhibiting high transmission in the Mid-Wave Infra-Red (MWIR) spectrum are often difficult to manufacture in large sizes with optimized physical and optical properties. In this work, we researched and developed improved tellurium-zinc-barium and lead-bismuth-gallium heavy metal oxide glasses for use in the manufacture of fiber optics, optical components and laser gain materials. Two glass families were investigated, one based upon tellurium and another based on lead-bismuth. Glass compositions were optimized for stability and high transmission in the MWIR. Targeted glass specifications included low hydroxyl concentration, extended MWIR transmission window, and high resistance against devitrification upon heating. Work included the processing of high purity raw materials, melting under controlled dry Redox balanced atmosphere, finning, casting and annealing. Batch melts as large as 4 kilograms were sprue cast into aluminum and stainless steel molds or temperature controlled bronze tube with mechanical bait. Small (100g) test melts were typically processed in-situ in a 5%Au°/95%Pt° crucible. Our group manufactured and evaluated over 100 different experimental heavy metal glass compositions during a two year period. A wide range of glass melting, fining, casting techniques and experimental protocols were employed. MWIR glass applications include remote sensing, directional infrared counter measures, detection of explosives and chemical warfare agents, laser detection tracking and ranging, range gated imaging and spectroscopy. Enhanced long range mid-infrared sensor performance is optimized when operating in the atmospheric windows from ~ 2.0 to 2.4μm, ~ 3.5 to 4.3μm and ~ 4.5 to 5.0μm.

Core-shell ZnO/γ-Fe₂O₃ nanoparticles were prepared via a simple method using forced hydrolysis of acetate metallic salts in a polyol medium. Two types of morphologies can be easily obtained: (i) quasi-spherical ZnO core 20 nm in diameter coated with a continuous shell with 3 nm in length, (ii) rod-like ZnO decorated with γ-Fe₂O₃ nanoparticles. The ZnO nanorods are 80 nm in diameter and 400 nm in length. The maghemite (γ-Fe₂O₃) nanoparticles with 5 nm in diameter are strongly bonded to ZnO, well separated from each other and form a monolayer on the surface of ZnO nanorods. In both systems, coating ZnO by γ-Fe₂O₃ inhibits the surface defects and thus enhances the UV luminescence. The two systems present a superparamagnetic behavior with blocking temperature depending on the morphology: the decorated ZnO nanorods present a blocking temperature around 6 K whereas this temperature is significantly higher (300 K) for spherical core-shell nanoparticles.

The influence of the metallic electrode materials on the contact resistance of the ink-jet printed In-Ga-Zn oxide (IGZO) thin film transistors (TFTs) is investigated in this paper. Various electrodes, including Al, Ti/Au, ITO and Au were examined based on the inverted staggered (bottom gate top contact) IGZO TFTs. Without additional annealing, the contact resistance increased with the increase of the work function of the electrode, which is Al < Ti/Au < ITO < Au. However, the contact resistance behavior changed drastically for different electrodes under different annealing temperature from 200 to 500 °C. The different behavior of the electrodes upon annealing was regarded to the contact modes changed between ohmic and Schottky contact. The finding provides a clue for electrode selection for the ink-jet printed IGZO TFTs to minimize the contact resistance and optimize the device performance according to the process conditions.

In this paper, a hybrid CMOS inverter employing In-Ga-Zn oxide (IGZO) (inorganic, n-channel) and P3HT (organic, p-channel) thin film transistors (TFTs) is reported. Both inorganic and organic TFTs are fabricated by ink-jet printing technology. The field effect mobility of p and n channel TFTs are 0.0038 and 0.27 cm²/V s, respectively. The inverter exhibited an obvious inverter response for switching between logic ‘1’ and logic ‘0’, and yielded a high gain of 14 at V_DD = 30 V. With the combining advantages of oxide semiconductor (n-type, high mobility) and organic (commonly p-type), it is promising to construct powerful functional CMOS circuits, such as ring oscillator and shift registers.

Aluminum doped zinc oxide (AZO) films with the aluminum concentration of 1.5 at.% were fabricated by co-sputtering dual metallic targets, Al and Zn, under the oxygen partial pressure of 1.3×10^-4 torr. The total pressure was kept at 2.3 ×10^-4 torr during the deposition. The poly-crystalline structure, optical property and conductivity of the films were investigated by XRD, UV-VIS-IR spectrometer and Hall measurement, respectively. The more intense ZnO crystallinity of (002), larger grain size, smaller d-spacing and highest carrier concentrations were observed on the as deposited AZO film which had the lowest resistivity of 7.8 ×10^-4 Ω•cm. Comparing the AZO films post-annealed in atmosphere, in vacuum and in hydrogen ambiance, the structures processed in vacuum and hydrogen ambiance remained the good ZnO crystallinity in the film resulting from the oxygen deficient state of the films after post annealing processes. The better thermal stability of resistivity was observed in the films post-annealed in hydrogen ambiance due to the formation of the shallow donor in the film. Furthermore, the resistivity increased as increasing the post-annealing temperature in atmosphere. When the as-deposited film were post-annealed at temperature of 400 °C, the resistivity was about more than two orders of magnitude than that of the as-deposited film resulting from the decrease of the donor concentration and mobility in the AZO film. The variation of the carrier concentration in the AZO film also shifted the energy band gap. However, the average visible transmittance of all AZO films in this study was above 80 % regardless of the deposition and post-annealing conditions.

Transparent conducting oxides have been widely employed in optoelectronic devices using the various deposition methods such as sputtering, thermal evaporator, and e-gun evaporator technologies.^1-3 In this work, gallium doped zinc oxide (ZnO:Ga) thin films were grown on glass substrates via H₂O-thermal atomic layer deposition (ALD) at different deposition temperatures. ALD-GZO thin films were constituted as a layer-by-layer structure by stacking zinc oxides and gallium oxides. Diethylzinc (DEZ), triethylgallium (TEG) and H₂O were used as zinc, gallium precursors and oxygen source, respectively. Furthermore, we investigated the influences of O₂ plasma post-treatment power on the surface morphology, electrical and optical property of ZnO:Ga films. As the result of O₂ plasma post-treatment, the characteristics of ZnO:Ga films exhibit a smooth surface, low resistivity, high carrier concentration, and high optical transmittance in the visible spectrum. However, the transmittance decreases with O₂ plasma power in the near- and mid-infrared regions.

This study investigates the temperature dependence of the current-voltage (I-V) characteristics of Al-doped Mg_xZn_1-xO/p-GaN junction diodes. Specifically, this study reports the deposition of n-type Al-doped Mg_xZn_1-xO (AMZO) films on p-GaN using a radio-frequency (RF) magnetron sputtering system followed by annealing at 700, 800, 900, and 1000 °C in a nitrogen ambient for 60 seconds, respectively. The AMZO/GaN films were thereafter analyzed using Hall measurement and the x-ray diffraction (XRD) patterns. The XRD results show that the diffraction angles of the annealed AMZO films remain the same as that of GaN without shifting. The n-AMZO/p-GaN diode with 900 °C annealing had the lowest leakage current in forward and reverse bias. However, the leakage current of the diodes did not change significantly with an increase in annealing temperatures. These findings show that the n-AMZO/p-GaN junction diode is feasible for GaN-based heterojunction bipolar transistors (HBTs) and UV light-emitting diodes (LEDs).

The bandgap control of doped-ZnO nanowires is important for tunable light emitting diodes (LEDs). Ultraviolet (UV), blue and violet LED structures based on Ag-doped ZnO /p-GaN and Cd-alloyed ZnO (Zn_1-xCd_xO) nanorods/p-GaN heterojunction have been fabricated by epitaxial electrodeposition at low temperatures and thermal annealing. UV electroluminescence (EL) peak around 397 nm observed from pure nanowires-ZnO/p-GaN at room temperature was shifted to 406 nm or 423 nm by using heterojunction between Ag-doped ZnO (ZnO:Ag) and Zn_1-xCd_xO-nanorods grown on p-GaN substrate, respectively. The electroluminescence emission threshold voltage was low at about 5.0 V and EL intensity increased with rise in the applied voltage bias. Presented experimental results demonstrate the tunable emission from silver and cadmium-doping in ZnO-based nanoLEDs.

ZnO has been a subject of intense research in the optoelectronics community owing to its wide bandgap (3.3eV) and large exciton binding energy (60meV). However, difficulty in doping it p-type posts a hindrance in fabricating ZnO-based devices. In order to make p-type ZnO films, phosphorus implantation, using plasma immersion ion-implantation technique (2kV, 900W, 10μs pulse width) for 30 seconds, was performed on ZnO thin film deposited by RF Magnetron Sputtering (Sample A). The implanted samples were subsequently rapid thermal annealed at 700°C and 1000°C (Samples B and C) in oxygen environment for 30 seconds. Low temperature (8K) photoluminescence spectra reveal dominant donor-bound exciton (D°X) peak at 3.36eV for samples A and B. However, for Sample B the peaks around 3.31eV and 3.22eV corresponding to the free electron-acceptor (FA) and donor to acceptor pair peaks (DAP) are also observed. A dominant peak around 3.35eV, corresponding to acceptor bound exciton (A°X) peak, is detected for Sample C along with the presence of FA and DAP peaks around 3.31eV and 3.22eV. Moreover, the deep level peak around 2.5eV is higher for Sample B which may be due to implantation and acceptor related defects. However, for Sample C, the deep level peaks are very weak compared to the near band edge peaks confirming that these peaks are mainly due to intrinsic defects and not related to acceptors. These results clearly show us a promising way to achieve p-type ZnO films using phosphorus doping.

Terbium-doped gadolinium oxysulfide (Gd₂O₂S:Tb) nanoparticles were synthesized by hydrothermal precipitation of urea. On the reaction, were analyzed variables as the temperature of solutions, the reaction time and the stirring velocities as main factors in the crystal growth. WAXD TEM and FTIR analysis were used to characterize the Crystallographic phase, morphology and chemical vibrations of the materials. Moreover, the photoluminescent properties were evaluated as response at the UV light, obtaining the main emission at 544 nm produced by ⁵D₄ → ⁷F₅ transition of the Tb³⁺ ions. Besides, we found that the host lattice and doped-ions concentration is essential to obtain a strong visible photoluminescence evaluated experimentally.

ZnO thin films were epitaxially grown on Zn-polar (0001) ZnO substrates by plasma-assisted molecular beam epitaxy. Surface root mean square (rms) roughness below 0.3 nm was achieved on a large range of growth temperatures by growing on ZnO substrates with 0.5 degree miscut angle toward [11¯00] axis. Surface treatment with acid etching and ozone exposure was required to remove contamination such as silica residual and carboxyl and carbonate groups on the surface. Removal of these surface impurities reduces the likelihood of extrinsic defect migration into the epitaxial films. High growth temperature (> 640°C) and oxygen rich conditions were required for films with terrace steps, but resulted in a very low growth rate (~30nm/h) and low photoluminescence (PL) lifetimes of lower than 50 ps. With moderate growth temperature (~610°C), higher growth rate and higher PL lifetime with up to 380 ps were achieved. EIT was used for the oxygen plasma to reduce reactive oxygen species etching of the surface, resulting in a higher growth rate and fewer defects in the films. Good crystalline quality was evident in Xray rocking curves with consistent narrow full width at half maximum (FWHM) of (0002), (101¯2) and (202¯1) peaks, indicating low threading dislocations. Both room-temperature and low-temperature photoluminescence indicated high optical quality of the resultant films with few non-radiative recombination centers.

In order to demonstrate tunable absorption characteristics of ZnO, photodetection properties of ZnO based thin-film transistors are investigated. By controlling the occupancy of the trap states, the optical absorption coefficient of ZnO in the visible light spectrum is actively tuned with gate bias. An order of magnitude change of absorption coefficient is achieved. An optical modulator is proposed exploiting such tunable absorption mechanism.

We performed a comprehensive study of the effect of transition metal oxide anode interlayer in bulk heterojunction solar cells based on P3HT:PCBM. We have investigated the influence of different metal oxides including tungsten oxide (WO₃), vanadium oxide (V₂O₅) and molybdenum oxide (MoO₃) on the solar cell performance. In addition, the influence of different deposition techniques (solution process and e-beam deposition/ thermal evaporation) has also been investigated. We found that deposition techniques play a significant role on the film quality and morphology and hence affect the photovoltaic performance. Obtained results are discussed in detail.

We investigated the influence of ITO properties on the performance of bulk heterojunction solar cells. The morphology, electrical and optical properties of ITO electrodes were characterized. The power conversion efficiency of cells made on different ITO substrates varied significantly from 2.3% to 3.1%. It was found that for a higher sheet resistance ITO substrate, the sheet resistance was the dominant parameter affecting the performance of the based solar cells, while for the lower ( below 20 ohm/square) sheet resistance, transmittance in the region where polymer strongly absorbs and the surface roughness of the substrate had significant effect on the solar cells performance.

MgZnO thin films were grown on c-sapphire and ZnO-coated c-sapphire substrates by pulsed laser deposition from a ZnMgO target with 4 at% Mg. The MgZnO grown on the ZnO underlayer showed significantly better crystal quality than that grown directly on sapphire. AFM studies revealed a significant deterioration in surface morphology for the MgZnO layers compared with the ZnO underlayer. Optical transmission studies indicated a MgZnO bandgap of 3.61eV (compared with 3.34eV for the ZnO), which corresponds to a Mg content of about 16.1 at%. The MgZnO/ZnO heterojunction showed an anomalously low resistivity, which was more than two orders of magnitude less than the MgZnO layer and an order of magnitude lower than that for the ZnO layer. It was suggested that this may be attributable to the presence of a 2D electron gas at the ZnMgO/ZnO heterointerface.

Transparent conducting metal oxides (TCO) are unusual semiconducting materials displaying transparency to visible light. TCO materials are used for electrostatic shielding, antistatic screens, transparent heating devices, solar cells and even organic light emitting diodes. However, most TCOs are n-type, while p-type TCOs are scarce. SrCu₂O₂ is a leading candidate as a p-type transparent conductive oxide. In this paper, we report theoretical calculations and experimental studies on the vibrational, optical and microstructural properties of both bulk and thin films of polycrystalline undoped SrCu₂O₂ obtained by pulsed laser deposition (PLD). Barium doping of the SrCu₂O₂ by substitution of Sr atoms is also reported. The simulated crystal structures of both SrCu₂O₂ and BaCu₂O₂ materials, obtained through a state-of-the-art implementation of the Density functional theory, are compared with experimental X-ray diffraction data of undoped and Ba-doped SrCu₂O₂ bulk materials. Raman spectra of both SCO and BCO materials are simulated from the derivatives of the dielectric susceptibility and a symmetry analysis of the optical phonon eigenvectors at the Brillouin zone center is proposed. Good agreement with Raman scattering experimental results is demonstrated.