We report the growth of HgCdTe by metal organic vapor phase epitaxy (MOVPE), using (211)B CdTe/Si substrates grown by molecular beam epitaxy (MBE). The surface morphology of these films is very smooth. Morphological defects are primarily oval type void defects with the density of 500cm^-2. The etch pit densities (EPD) and full widths at half maximum (FWHM) of x-ray rocking curves exhibit that the grown epilayers replicate exactly the structural properties of substrate. The Hall parameters of undoped HgCdTe layers show anomalous n-type behavior with temperature. Long time annealing under Hg-saturated condition found to deteriorate the transport properties of HgCdTe layers resulting from the possible in corporation of impurities in the layers. Mid wave infrared (MWIR) photovoltaic devices have been fabricated from n on p HgCdTe films. The MOVPE grown films were processed into mesa type discrete devices with wet chemical etching employed for mesa delineation and ZnS surface passivation. The dynamic resistance-area product at zero bias voltage for a temperature of 77K is 4000 ohm-cm². But R_oA values are scattered drastically. In some detectors, R_oA values are less than 100 ohm-cm². It is thought that these results are related with localized defects or anomalous transport properties of epilayer.

We have carried out basic research on the extrinsic p-type doping of mercury cadmium telluride epilayers grown by molecular beam epitaxy. The doping is performed with elemental arsenic and gold sources. HgCdTe epilayers of CdTe mole fraction in the range of the long-wavelength and mid-wavelength infrared were grown on (211)B CdTe/Si and CdZnTe substrates. The van der Pauw technique was utilized to study the temperature dependent Hall effect characteristics of the grown epilayers and the photoconductive decay method was used to obtain minority carrier lifetime data. Activation annealing of As at different temperatures was performed. P-type conversion of As doped samples at lower than conventional annealing temperatures was achieved. The influence of the annealing conditions on the Hall effect characteristics of the grown epilayers were studied. As activation in HgCdTe is also studied in the annealing experiments and compared to the current As activation models. We studied the surface and the bulk properties of our p-type doped samples by minority carrier lifetime measurements. Gold doping was achieved by deposition of Au on and its diffusion into samples. We also investigated the effects of vacancies on the mobility of Au dopants in the HgTe lattice by ab-initio pseudo-potential methods. For this study, we first determined the smallest supercell that will produce reliable results. Then total energy calculations were performed on supercells with nearest neighbor, 2^nd nearest neighbor, 3^rd nearest neighbor, etc. vacancies relative to Au sites.

This paper describes some recent results on surface defects, uniformity, dislocation density as well as device applications of MBE growth of HgCdTe at the research center of advanced materials and devices. The features of different surface defects and their origins were studied by using SEM/EDX observations on HgCdTe epilayers with different growth conditions. A variety of surface defects was observed and the formation mechanism was discussed. A good uniformity was observed over 3-in HgCdTe wafers, the Stddev/mean in x and thickness were 1.2%, and 2.7%, respectively. It was found that the dislocation density was sensitive to growth parameters and the composition. The ZnCdTe substrates with 4% mole fraction were found to be suitable for LW HgCdTe, however, for the HgCdTe of shorter wavelengths different Zn composition is required. An average value of EPD of 4.2×10⁵cm⁻² was obtained for LW samples. The MBE grown HgCdTe were incorporated into some preliminary FPA devices.

Ion implantation enhanced intermixing of quantum well has become an important technology in device fabrication and material modification. We report the intermixing effect in a single asymmetric coupled quantum well (GaAs/AlGaAs) at different ion implantation dose by photoluminescence. More than 80meV of blue shift of the interband transition was observed before rapid thermal annealing process. It indicates that the intermixing has almost finished during the implantation process. A diffusion length of 1nm is obtained by the theoretical analysis.

Quantum well infrared photodetectors (QWIP) are flexible in tailoring their characteristics to suit an application. In this article, we present a design and optimization concept to construct an infrared spectrometer. It utilizes the broadband absorption of a QWIP and the narrow band light coupling of a grid structure. The QWIP material defines the range of detection wavelengths of the spectrometer while the grid geometry selects out different wavelengths to detect in different detector elements. We will present specific design examples in two wavelength ranges, one from 7.5 to 12 μm and another from 6 to 15 μm. We will also present some experimental results to support the design feasibility.

The optimal performance of VLWIR (15 μm cutoff wavelength) photovoltaic detectors is assessed theoretically. The electronic band structures are computed with a fourteen-band restricted-basis envelope function Hamiltonian that includes terms copuling heavy and light holes at the superlattice interfaces. These terms describe the type of bonding at the interfaces (InSb or GaAs-like) and result in approximately 25 meV energy gap corrections in thin superlattices in comparison with conventional envelope-function approaches that neglect these terms. Auger lifetimes and upper bounds to detector detectivities are computed with these accurate band structures. The Auger transition rate calculations include Umklapp terms in the transition amplitude.

A type of high accuracy infrared spectroscopic ellipsometer, by fixed polarizer, rotating polarizer, sample and fixed analyzer PP_r(ω)SA, has been designed and constructed to study the optical properties of infrared materials in the 2.5 - 12.5 μm wavelength range. The ellipsometric parameters ψ and Δ can be derived directly from the detected signal by two ac components with the frequencies of 2ω and 4ω, avoiding measuring the dc component in addition. The system operations, including data acquisition and reduction, pre-amplifier gain control, incident angle, as well as wavelength setting and scanning, were fully and automatically controlled by a computer. The accuracy in straighthrough is better than 1% on tanψ and cosΔ without any defect correction of instrumental elements, which is quite good for the infrared optical constants measurements. Some typical applications on ferroelectric thin films PZT and BST and narrow gap semiconductors Hg_1-xCd_xTe are presented.

Some new results about the optical and electronic characterization on HgCdTe materials have been reported in this paper. The photoluminescence measurements for HgCdTe sample have been performed to characterize the impurities states in HgCdTe and the quality of the crystal perfection. The optical constants in the energy region below, near and above the energy gap for Hg_1-xCd_xTe materials have been investigated by infrared spectroscopic ellipsometry measurements using a monochromatic dispersion infrared ellipsometer in the wavelength region of 2 to 12.5μm. Variable magnetic field Hall measurements (0-10T) were performed on MBE-grown Hg_1-xCd_xTe films and on boron ion implanted bulk n-type Hg_1-xCd_xTe at various temperatures (1.2 ~300K). By a hybrid approach consisting of mobility spectrum (MS) analysis followed by a multi-carrier fitting (MCF) procedure, the contributions to the total conductivity arising from all kinds of carriers in the sample including in the bulk and on the surface layer have been separated. The Cd composition distribution image for HgCdTe sample has been realized by using a thermal image system from measuring the transmittance distribution and calculating the composition distribution.

A Woollam M88 spectroscopic ellipsometer was used to characterize the molecular beam epitaxy growth nucleation of Hg_1-xCd_xTe layers on CdZn_0.035Te substrates and the substrate temperature prior to the growth. We developed a new approach to ellipsometry data analysis to better determine the substrate temperature. It is based on the accurate determination of the critical point energies and linewidths, which display strong temperature dependence in the CdZnTe system. The new model was able to resolve temperature differences of the order of +/-2.5^oC. We also show that ellipsometry can be used to characterize the nucleation of Hg_1-xCd_xTe on CdZnTe substrates. More work is in progress to assess the run-to-run reproducibility of our temperature measurement, and to further investigate Hg_1-xCd_xTe nucleation.

The dislocations in HgCdTe films grown by LPE on CdZnTe (111)B substrates were studied by chemical etching. Among the etchants used for HgCdTe materials before, it was found that the Schaake etchant was an effective method to reveal the dislocations of HgCdTe (111)B films with a thickness over 5μm. Besides of the threading dislocations as reported before, another kind of dislocations induced by the stress was also observed by using Schaake etchant. Large quantities of such dislocations were observed in the areas nearby the melt droplet left on the LPE film and cutting line and on the surfaces of the HgCdTe films annealed by using a cap layer and unsuitable transportation of samples. The measurements of the depth profiles of the EPDs show that the most of the stress-induced dislocations are located in the surface layer and its density can be as high as 10⁷cm^-3. Whereas the EPD of the threading dislocation doesn't change a lot along the depth of the film in usual case. The Chen etchant can also be used to reveal the threading dislocations of the films thicker than about 10μm. The phenomena of two kinds of etch pits was also observed on the surface of HgCdTe film etched by the Chen etchant. The etch pit densities originated from threading dislocations are approximately the same for both etchants. But the stress-induced dislocations in the surface layer were not observed by using the Chen etchant except the area near the melt droplet.

Specially designed mercury cadmium telluride (Hg_1-xCd_xTe) p-ν-n⁺ heterostructures were grown by molecular beam epitaxy (MBE) on CdTe/Si and CdZnTe (211)B-oriented substrates for infrared photo-detector operation at near room temperature. Growth of this structure requires precise control over the crystal quality, compositional profiles, and donor and acceptor doping levels. The doping levels and density of Shockley-Read-Hall centers in the absorber layer must be low enough to realize the benefits of Auger suppression under non-equilibrium device operation. In order to avoid possible contamination from chemical compounds used in traditional substrate mounting methods, non-contact (In-free) substrate mounting was used to grow the structures. High-energy electron diffraction (RHEED) was implemented to develop a substrate thermocouple temperature ramping curve that maintains a constant epilayer temperature. The structures were characterized by FTIR, x-ray diffraction, and temperature dependent Hall measurements. High operating temperature (HOT) detectors were fabricated on these materials and showed good room-temperature response.

This paper discusses the potential thermal imaging performance achievable from thermal detector arrays and concludes that the current generation of thin-film ferroelectric and resistance bolometer based detector arrays are limited by the detector materials used. It is proposed that the next generation of large uncooled focal plane arrays will need to look towards higher performance detector materials - particularly if they aim to approach the fundamental performance limits and compete with cooled photon detector arrays. Two examples of bolometer thin-film materials are described that achieve high performance from operating around phase transitions. The material Lead Scandium Tantalate (PST) has a paraelectric-to-ferroelectric phase transition around room temperature and is used with an applied field in the dielectric bolometer mode for thermal imaging. PST films grown by sputtering and liquid-source CVD have shown merit figures for thermal imaging a factor of 2 to 3 times higher than PZT-based pyroelectric thin films. The material Lanthanum Calcium Manganite (LCMO) has a paramagnetic to ferromagnetic phase transition around -20^oC. This paper describes recent measurements of TCR and 1/f noise in pulsed laser-deposited LCMO films on Neodymium Gallate substrates. These results show that LCMO not only has high TCR's - up to 30%/K - but also low 1/f excess noise, with bolometer merit figures at least an order of magnitude higher than Vanadium Oxide, making it ideal for the next generation of microbolometer arrays. These high performance properties come at the expense of processing complexities and novel device designs will need to be introduced to realize the potential of these materials in the next generation of thermal detectors.

Columnar Ba_0.8Sr_0.2TiO₃ films with a grain size of 100 to 200 nm have been obtained from a 0.05M precursor solution. Electrical measurements indicated these films showed a pyroelectric coefficient of 4.1 × 10^-4 C/m²K at room temperature, and a leakage current of 1.42 × 10^-7 A/cm² under 100 kV/cm electrical field. The Ba_0.8Sr_0.2TiO₃ films have been used for fabricating a 1 × 16 elements infrared detector linear array with a bulk micromachining technique. The array pixels with a sensitive area of 500 × 300 μm² have a detectivity of 2.3 × 10⁸ cmHz^½W^-1 at 23°C and 35 Hz. By using these infrared detector arrays, thermal images were successfully obtained at room temperature. These results indicate the sol-gel derived Ba_0.8Sr_0.2TiO₃ films from a 0.05M precursor solution are suitable for uncooled infrared detector array applications.

Pyroelectric properties in alternating DAEP/NC Langmuir-Blodgett (LB) films and effects of incorporating the barium cations on pyroelectric behaviors have been investigated. Its pyroelectric coefficient measured is found to be 58μC m^-2 K^-1at 300K. The dielectric properties have been measured and used to determine the figures of merit in thermal devices. Relative permittivity ε_r and dielectric loss values tanδ of pyroelectric films (in the range of 1KHz - 100KHz) are 2.34~1.96 and 0.08~0.04, respectively. These data give a maximum pyroelectric figure of merit of 150μC m^-2 K^-1 in the alternating LB films incorporating barium ions. The effects of different deposition on pyroelectric properties are also discussed in this paper. It is indicated that the alternating LB films is promising in the field of pyroelectricity and pyroelectric infrared detector.

CdTe films have been electrodeposited on HgCdTe from ethylene glycol based electrolyte containing 50 mM CdSO₄, 10 mM K₂TeO₃ and 0.1 M HClO₄. Deposition potential range with respect to a saturated calomel reference electrode was determined through cyclic voltammetry technique. RBS data showed that films deposited at potential range between -0.4 to -0.5 V have nearly stoichiometric Cd/Te atomic ratio. At the same time, highly oriented and smoother films were obtained at potential range were stoichiometric CdTe films were electrodeposited through nitrogen bubbling process. By adopting constant potential deposition technique could be obtained between electrodeposited CdTe and HgCdTe substrate showing high frequency capacitance-voltage (C-V) characteristics. Electrodeposited CdTe film can be used as a passivant for LWIR HgCdTe photodiodes.

II-VI intrinsic very long wavelength infrared (VLWIR, λ_c~20 to 50 μm) materials, HgCdTe alloys as well as HgCdTe/CdTe superlattices, were grown by molecular beam epitaxy (MBE). The layers were characterized by means of X-ray diffraction, conventional Fourier transform infrared spectroscopy, Hall effect measurements and transmittance electron microscopy (TEM). Photoconductor devices were processed and their spectral response was also measured to demonstrate their applicability in the VLWIR region.

Factors that affect width and aspect ratio in electron cyclotron resonance (ECR) etched HgCdTe trenches are investigated. The ECR etch bias and anisotropy are determined by photoresist feature erosion rate. The physical characteristics of the trenches are attributed to ECR plasma etch chemistry.

Investigations of performance of mercury cadmium telluride (MCT) multipixel arrays at T≈80 K are considered. MCT hybrid arrays for long-wavelength infrared (LWIR) applications with n⁺-p-diodes and n-channel charged coupled devices (CCD) silicon readouts were designed, manufactured and tested. For testing procedure the measurements of noise and signal-to-noise ratio (SNR) are the key issues to determine performance parameters to characterize IR-sensors. That puts certain requirements to the registration system and methods of measuring used. The noise of the signals from LWIR-photodiodes with CCD readouts or CCD readouts itself was measured using several different techniques. To find out and eliminate noise sources the spectral noise power of signals was analyzed. It allowed the possibility to implement actions for reducing of the registration system noise, and to define the software noise filters to be used. The testing procedure of FPA performance characteristics includes the measurements of detectivity D*, noise equivalent temperature difference NETD, cut-off wavelength and some other parameters of the arrays.

Reactive ion etching (RIE) is known to type convert p-type HgCdTe to n-type, thus providing a method for p-n junction formation for photodiode fabrication. Mid-wavelength infrared (MWIR) n-on-p photodiodes fabricated using RIE induced p-to-n type conversion have already been demonstrated and show excellent performance. This paper will report on the successful application of RIE junction formation technology for long-wavelength infrared (LWIR) HgCdTe photodiodes, and compares the device performance of photodiodes fabricated on vacancy and extrinsically doped p-type HgCdTe. The diode current versus bias voltage (I-V) characteristic of these devices have also been measured as a function of temperature in the range 20K to 200K with various junction areas. These results are compared in the light of detailed Hall measurement data obtained from type converted materials.

The results of the investigation of the properties of a-SiGe:H/c-Si heterostructures fabricated by LF (55 kHz) PECVD are presented. The investigation of spectral characteristics of a-SiGe:H/c-Si heterostructure in the wavelength range from 500 to 1100 nm showed that the short-wave absorption edge is determined by optical gap of a-SiGe:H alloy. The position of maximum of specific photosensitivity shifts from 830 to 940 nm with the increase of germanium concentration in the a-SiGe:H alloy. It was established that in a-SiGe:H/c-Si heterostructures the multitunnelling capture-emission mechanism prevails in low voltage range (less than 1.0 V). In this case the emission of holes to the valence band of a-SiGe:H from the defect states caused by Ge dangling bonds predominate. When applied voltage is more than 1.5 V, space charge limited current is observed. In this case the rise of the current is provided by the thermal emission of electrons from the defect states associated with Si dangling bonds in the upper half of a-SiGe:H.

Active films coatings on porous silicon (PS) surface from semiconductors and dielectrics such as cadmium-mercury-telluride (CMT) narrow band semiconductors, oxide (Al₂O₃), chalcogenide materials (ZnS, CdTe), polymer and GaSe films were created. Possibility of optocouple creation for the wide spectral range (as light emitter and detector) from infrared to UV was considered. Photoluminescence, electroluminescence, photosensitivity of porous silicon (PS) were investigated. Light-emission and photosensitivity spectra such heterostructures in visible and infrared region were investigated. The principal properties of created grade-band heterostructure with monotonically increasing energy gap from 0.3-0.4 eV (CMT) to 2.8-3.0 eV (PS) showed the reaction of charge transferring on UV and visible light irradiation. The thermostimulated depolarization (TSD) spectra of PS in the range of temperatures 77-450 K were investigated.

The Cd-annealing effects on Cd_1-xZn_xTe wafers were studied by means of IR transmission and micro-Raman spectrum. The experiments and theoretical analysis demonstrated that the free carrier absorption related to the Cd vacancies resulted in the IR extinction as observed in the transmission spectra. The Raman spectra showed that Raman scattering is a more sensitive method to detect the fine Te precipitates in the Cd_1-xZn_xTe substrates. The Raman scattering peaks related to the Te precipitates could be found in both the as grown and the annealed samples. The relative intensity of the Te scattering peaks became weaker after Cd-annealing. This result also indicated that it was quite difficult to eliminate the fine Te precipitates entirely through annealing process.

In this paper, a thin PbTiO₃-n-p⁺ silicon switch sensor has been developed, in which the switching voltage (the turned-on voltage) changes in proportion to the infrared light power. The sensor has a rapid response time of 0.65 μs compared with other conventional infrared sensors. It is attributed to the rapid switching device structure and the smaller pyroelectric layer thickness, 50 nm. Meanwhile in this paper, we have successfully analyzed the rapid switching transient response by using heat conduction and switching theory. The experimental results are in agreement with the theoretical analysis.

In this paper, a new pin/MISS photoreceiver with very high output current has been developed successfully by using the combination of the amorphous silicon germanium alloy pin photodiode and metal insulator semiconductor switch (MISS) device. The developed photoreceiver uses the pin photodiode as the light absorption structure and light wavelength selector and the MISS device as the photocurrent amplifier. Based on the experimental results, the photoreceiver yields a very high output current of 3.2 mA at a voltage bias of 6V under an incident light power P_in equals 100 μW and has a rise time of 465 μs at a load resistance R equals 1 KΩ. The peak response wavelength of the diode is at 905 nm, i.e. infrared light. Thus the high output current pin/Miss photoreceiver provides a good candidate for the IR OEIC's applications.

Since influences of each factor on temperature increase can be reflected by heat flow equation, study of it is helpful to optimal design for uncooled infrared focal plane arrays (UIFPA). But presently there is no more particular discussion of heat flow equation and no frank graphs as reference. In this paper particular discussions of influencing factors are given and for the first time 2-D and 3-D graphs are used to frankly show the degree of influences from different angle of view. Schemes on the optimal design of UIFPA are also given. According to graphs the maximum of temperature increase is obtained only when UIFPA is modulated at certain value which is less than cut-off modulation frequency. In 3-D graphs distinct curves are obtained in different range of thermal conductance and heat capacity and the optimal temperature increase value is achieved only when thermal conductance and heat capacity make thermal response time meet optimal condition. Optimal condition and formula can be deduced with given graphs and multifold approaches of optimal design of thermal isolation structure are discussed. It is proved that in optimal condition temperature increase can achieved 10^-1 level. It is clear that data provided by 2-D and 3-D graphs is valuable to evaluate optimal range for UIFPA.

We report the growth of short wave infrared (SWIR) HgCdTe on (001) GaAs by metal organic vapor phase epitaxy (MOVPE). KOH dissolved in water used as final substrate rinse produce a mirror - like surface and with a hillock density of less than 10cm⁻². It is shown that K element diffuses during layer growth and heat treatment for metal vacancy filling from the GaAs substrate/buffer interface into the MCT with a surface concentration of around low 10¹⁵cm⁻³. The transport properties of undoped MCT layers are dominated by residual K element in the layer. Short wave infrared (SWIR) photovoltaic devices have been fabricated from n on p HgCdTe films on GaAs substrates. The MOVPE grown films were processed into mesa type discrete devices with wet chemical etching employed for mesa delineation and ZnS surface passivation. The photodiode forward and reverse current-voltage characteristics, as well as the temperature dependence of the zero-bias dynamic resistance, were measured in the temperature range of 200-300 K. The zero bais dynamic resistance-area product at 200K and 300K were 5×10⁵ and 3.0×10² ohm-cm², respectively. The relative spectral response cut off wavelength of device at 300K was 2.5μm.

Steady state minority carrier lifetime has been investigated in heterostructure HgCdTe devices fabricated on Molecular Beam Epitaxy (MBE) grown material. Wider band gap Hg_(1-x)Cd_(x)Te x = 0.44 was MBE grown on narrower gap Hg_(1-x)Cd_(x)Te x = 0.32 material to create an abrupt interface. Both layers were unintentionally doped n-type as determined by Hall measurements, which show two distinct electron species corresponding to the two HgCdTe layers. Steady state lifetime as a function of temperature over the range 80K to 300K was extracted from responsivity and noise measurements performed on variable area photoconductor structures fabricated on the sample. At 80K, the photoconductors exhibit a specific detectivity at 1kHz of 4.5 x 10¹¹ cmHz^-1W^-1. For each measurement temperature, the steady state excess carrier lifetime determined experimentally was compared to the theoretical bulk lifetime for material with x = 0.32 and effective n-type doping density of 3.7 x 10¹⁴cm^-3. For temperatures below 180K, measured lifetime is in agreement with bulk lifetime of ~12μs, however, for higher temperatures there is evidence of an additional mechanism which reduces the apparent lifetime in the material. It is concluded that for temperatures above 180K, there is significant thermally induced promotion of photogenerated carriers from the narrow bandgap material into the wide bandgap material, leading to a reduction in the responsivity of the detector due to the relatively high doping of the wide bandgap layer.