Isothermal Vapor Phase Epitaxy Research Articles

Nanotechnological Enhancement of Infrared Detectors by Plasmon Resonance in Transparent Conductive Oxide Nanoparticles

We investigated theoretically and experimentally the use of nanotechnology to enhance the performance of semiconductor infrared detectors. An increase of the quantum efficiency, responsivity and specific detectivity is obtained by applying transparent conductive oxide (TCO) nanoparticles onto the surface of a photodetector. To this purpose we considered uncooled mercury cadmium telluride (HgCdTe) photoconductive detectors fabricated by isothermal vapor phase epitaxy, but the same procedure can be applied to cryogenically cooled devices, including those of photovoltaic type. The main mechanism of enhancement is light concentration ensured through localized plasmon resonance at the TCO nanoparticles and through enhanced scattering, while the desired wavelength range is reached by a further redshifting through the adjustment of nanoparticle properties. The improvement can be implemented duringthe final stages of production of the existing photovoltaic and photoconductive detectors. The method is applicable to various practical applications, including updating of high-precision guided ammunition.

Transition from a disordered to a crystalline state in II–VI and III–V films

The initial stages of HgCdTe growth on Al2O3, GaAs, CdTe, and KCl substrates have been studied by electron diffraction. HgCdTe films were produced by pulsed laser deposition and isothermal vapor phase epitaxy. InGaAs films were grown by isothermal chloride epitaxy on GaAs substrates. In the initial stages of the growth process, we observed a transition from an amorphous to a textured polycrystalline phase and then to a mosaic single-crystal structure. We have calculated the critical size of crystalline grains below which amorphization occurs in II-VI and III-V compounds. The critical grain size agrees with the grain size of the disordered (amorphous) phase that forms in the initial stage of epitaxy. We have determined some characteristics of the heterostructures: critical film thickness below which pseudomorphic growth is possible without misfit dislocation generation, elastic stress in the epitaxial system, surface density of dangling bonds at dislocations, and the critical island radius above which no interfacial misfit dislocations are generated.

Growth kinetics of ISOVPE HgCdTe epilayers obtained on alloyed CdTe substrates with different crystalline orientations

Hg 1- x Cd x Te (MCT) epilayers were grown on (1 1 1)Cd, (1 1 1)Te, (1 1 0) and (1 0 0) CdZnTe and CdTeSe substrates by isothermal vapor phase epitaxy (ISOVPE). The growth kinetics of the epilayers were studied by a non-linear diffusive convective model for the ISOVPE MCT growth, which was assessed in a previous paper . The non-linear diffusion–convection problem, which describes ISOVPE MCT film growth, was numerically solved by means of discrete mathematics. As the theoretical and experimental composition profiles were remarkably different in accordance with the epilayers grown over pure CdTe substrates, in the model a finite rate in the surface reaction rate constant that enabled a good fit was assumed. The numerical value of the surface reaction rate constant was similar for all the studied substrates and crystalline orientations, hence the results enabled us to determine that the deposition rate has a mixed control for the experimental conditions of this work. This isotropic characteristic of the ISOVPE technique for pure and alloyed CdTe substrates is remarkable, quite different from other MCT growth techniques as MBE or MOCVD.

History of HgTe-based photodetectors in Poland

AbstractIn Poland, the HgCdTe studies began in 1960 at the Institute of Physics, Warsaw University. The material processing laboratory was created by Giriat and later by Dziuba, Gałązka, and others. Bridgman technique with sealed thick wall quartz ampoules was used to grow material suitable for research and experimental devices. Among the first papers published in 1961 and 1963 there were the Polish works devoted to preparation, doping, and electrical properties of HgCdTe.Infrared detector’s research and development efforts in Poland were concentrated mostly on uncooled market niche. At the beginning, a modified isothermal vapour phase epitaxy has been used for research and commercial fabrication of photoconductive, photoelectromagnetic and other HgCdTe devices. Bulk growth and liquid phase epitaxy were also used. Recently, the fabrication of infrared devices relies on low temperature epitaxial technique, namely metalorganic vapour phase deposition.At present stage of development, the photoconductive and photoelectromagnetic (PEM) detectors are gradually replaced with photovoltaic devices which offer inherent advantages of no electric or magnetic bias, no heat load and no flicker noise. Potentially, photodiodes offer high performance and very fast response. However, conventional photovoltaic uncooled detectors suffer from low quantum efficiency and very low junction resistance. The problems have been solved with advanced band gap engineered architecture, multiple cell heterojunction devices connected in series, and monolithic integration of the detectors with microoptics.In final part of the paper, the Polish achievements in technology and performance of HgMnTe and HgZnTe photodetectors are presented.

ISOVPE MCT films grown on pure and alloyed CdTe substrates with different crystalline orientations

Epitaxial films of Hg 1− x Cd x Te (MCT) with x≅0.2 were grown on CdTe, Cd 0.96Zn 0.04Te and CdTe 0.96Se 0.04 substrates by the isothermal vapor phase epitaxy (ISOVPE) technique with no mercury overpressure. The growth was accomplished in different crystallographic orientations: (1 1 1)Cd, (1 1 1)Te, (1 1 0) and (1 0 0). The structural characterization of substrates and films was performed by X-ray diffraction (Laue technique), surface chemical etching and optical microscopy. Chemical composition analysis was performed by an electronic microprobe in the wavelength dispersive spectroscopic mode and electrical characterization by Hall effect measurements. MCT is an important semiconductor for the manufacture of infrared detectors. The alloyed substrates have a closer lattice match with Hg 1− x Cd x Te. Furthermore, these substrates usually have a lower dislocation density. Both facts determine a lower generation of lineal defects during growth. This fact could produce a larger carrier lifetime and, as a consequence, better electrical properties of devices. On the other hand the surface morphology of ISOVPE MCT epitaxial films only depends on the crystallographic orientation, being independent of the use of pure or alloyed substrates.

Uncooled infrared photodetectors in Poland

AbstractThe history and present status of the middle and long wavelength Hg1-xCdxTe infrared detectors in Poland are reviewed. Research and development efforts in Poland were concentrated mostly on uncooled market niche.Technology of the infrared photodetectors has been developed by several research groups. The devices are based on mercury-based variable band gap semiconductor alloys. Modified isothermal vapour phase epitaxy (ISOVPE) has been used for many years for research and commercial fabrication of photoconductive, photoelectromagnetic and other devices. Bulk growth and liquid phase epitaxy was also used. At present, the fabrication of IR devices relies on low temperature epitaxial technique, namely metalorganic vapour phase deposition (MOCVD), frequently in combination with the ISOVPE.Photoconductive and photoelectromagnetic detectors are still in production. The devices are gradually replaced with photovoltaic devices which offer inherent advantages of no electric or magnetic bias, no heat load and no flicker noise. Potentially, the PV devices could offer high performance and very fast response. At present, the uncooled long wavelength devices of conventional design suffer from two issues; namely low quantum efficiency and very low junction resistance. It makes them useless for practical applications. The problems have been solved with advanced 3D band gap engineered architecture, multiple cell heterojunction devices connected in series, monolithic integration of the detectors with microoptics and other improvements. Present fabrication program includes devices which are optimized for operation at any wavelength within a wide spectral range 1–15 μm and 200–300 K temperature range. Special solutions have been applied to improve speed of response. Some devices show picoseconds range response time. The devices have found numerous civilian and military applications.

Growth and characterization of Hg1-xCdxTe epitaxial films by isothermal vapour phase epitaxy (ISOVPE)

Growth of Hg1-xCdxTe epitaxial films by a new technique called asymmetric vapour phase epitaxy (ASVPE) has been carried out on CdTe and CZT substrates. The critical problems faced in normal vapour phase epitaxy technique like poor surface morphology, composition gradient and dislocation multiplication have been successfully solved. The epitaxial films have been electrically characterized by using the Hall effect and capacitance-voltage (C-V) measurements.

Growth of Hg<sub>1-x</sub>(Cd<sub>1-y</sub>Zn<sub>y</sub>)<sub>x</sub>Te on Si(111) by Isothermal Vapor Phase Epitaxy

The quaternary HgCdZnTe (MCZT) epilayer was successfully grown on lattice matched Cd0.96Zn0.04Te/Si(111) substrates using isothermal vapor phase epitaxy (ISOVPE) method. It was found that Si wafer is an excellent barrier against Hg and Cd diffusion. Cross-sectional images reveal a flat and well-distinguished interface between MCZT and Si, and voids formed due to interdiffusion was not observed in MCZT layer above the Si wafer. It was demonstrated that it was possible to yield an almost homogeneous MCZT epilayer without compositional gradient by selecting suitable growth time.

Properties of Hg1‐xCdxTe epitaxial films grown on (211)CdTe and (211)CdZnTe

AbstractHg1‐xCdxTe (MCT) epitaxial films have been grown employing single crystalline substrates of CdTe and Cd0.96Zn0.04Te with (211)Cd and (211)Te crystalline orientations. The Isothermal Vapor Phase Epitaxy (ISOVPE) technique without Hg overpressure has been used for the epitaxial growth. Substrates and films were characterized by optical microscopy, chemical etching and x ray diffraction (Laue technique). The electrical properties were determined by Hall effect measurements. The characterization results allowed to evaluate the crystalline quality of MCT films. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

The effect of built-in electric field on As diffusion in HgCdTe graded-band-gap epitaxial layers

Experiments have been carried out on As diffusion in graded-band-gap HgCdTe epitaxial layers grown by isothermal vapor-phase epitaxy (ISOVPE). For studying As and Hg concentration distribution on depth, the SIMS experimental technique was used. A non-monotonous profile of As concentration distribution has been revealed, with the maximum distribution approximately located in the region at the edge of a sharp change in composition. A model describing the influence of the built-in electric field caused by the spatial inhomogeneity of energy gap on the diffusion of the charged impurity has been proposed. A comparative analysis of theoretical and experimental data has been performed.

Defect Distribution and Properties of (211) ISOVPE-MCT Films

Epitaxial films of Hg1−xCdxTe(MCT)were grown by Isothermal Vapor Phase Epitaxy(ISOVPE)without Hg overpressure on single crystalline substrates of CdTe and Cd0.96Zn0.04Te with(211)Cd and(211)Te crystallographic orientations. The chemical composition profile was determined using an electronic microprobe on the {110} preferential cleavage surfaces. Experimental values and data from the literature were used to calculate the percentage relative misfit and microhardness profiles. Both were correlated with the misfit dislocations distribution obtained at the interface of the films by chemical etching. The Zn doping in pure CdTe is related with the defect distribution at the film-substrate interface.

Observation of CuPt and CuAu I-type ordered structure in HgCdTe grown by isothermal vapour phase epitaxy

Ordered structures, CuPt and CuAu I types in HgCdTe are reported for the first time. Hg 1− x Cd x Te thin crystals were grown by isothermal vapour phase epitaxy (ISOVPE) method on a CdTe substrate and they were observed by transmission electron microscopy (TEM) in planar view and cross-sectional geometries. Two variants of CuPt-type ordered structure were found in different microdomain sets on HgCdTe. Another superstructure observed was the CuAu I-type coexisting with CuPt domain structure.

Transmission electron microscopy of the induced damage by argon implantation in (111) HgCdTe at room temperature

HgCdTe (MCT) is an important semiconductor material used for infrared photovoltaic detectors. Although ion implantation is a widely used technique in the manufacture of devices based on MCT to obtain n/p junctions, a detailed understanding of the n-type behavior of the unannealed damage region has not yet been established. In this work, n/p junctions were formed by Ar++ implantation on MCT (111) grown by the isothermal vapor phase epitaxy method. Structural damage after implantation for different implantation doses (1013, 1014, and 1015 Ar++/cm2) was evaluated by transmission electron microscopy. At high doses, damage distribution exhibits a double region of defects. These were mainly vacancy dislocation loops and lines in the first region, whereas the second zone exhibited small dislocation loops. The observed n-type behavior after implantation was attributed to the generation and diffusion of Hg from the damaged region.

Ar-implanted epitaxially grown HgCdTe: evaluation of structural damage by RBS and TEM

Mercury cadmium telluride alloys Hg 1− x Cd x Te (MCT) is an important semiconductor material used in infrared photovoltaic detectors. Although ion implantation is a widely used technique in the manufacture of devices based on MCT, a detailed understanding of the n-type behaviour of the unannealed damage region has not yet been established. In the present paper n on p junctions were formed by Ar ++ implantation on MCT(1 1 0) grown by isothermal vapour phase epitaxy method (ISOVPE). Comparison of the structural damage after implantation is evaluated by Rutherford backscattering spectrometry (RBS) and transmission electron microscopy (TEM) measurements for different doses. Damage distribution presents two peaks and defects are primarily vacancy dislocation loops in the first region. The observed n-type behaviour after implantation is attributed to the generation and diffusion of Hg from the damage region.

Growth of Hg 1− x(Cd 1− yZn y) xTe epilayers on (100) Cd 1− yZn yTe/GaAs substrates by ISOVPE

Hg 1− x Cd x Te (MCT) and Hg 1− x (Cd 1− y Zn y ) x Te (MCZT) epilayers were grown by isothermal vapor phase epitaxy (ISOVPE) using CdTe and lattice matched Cd 1− y Zn y Te ( y≈0.045, CZT) layers, respectively, of various thickness on (100) GaAs as substrate. The problems of void formation and Ga outdiffusion can be overcome by using a sufficiently thick substrate layer. The ISOVPE epilayers show improved quality compared with substrate and their quality was found to be independent of substrate. It was found that FWHM values for MCZT epilayers grown on lattice matched CZT/GaAs were 70–90 arcsec, smaller than those reported here for MCT/CdTe/GaAs. Despite the broader FWHM for CZT/GaAs, a significant improvement in the quality of ISOVPE MCZT epilayers grown on these substrates was observed. This result is mainly attributed to the smaller lattice mismatch and the effect of Zn addition compared with MCT/CdTe.

Effect of lattice match and Zn addition on the properties of Hg 1− x(Cd 1− yZn y) xTe epilayers grown by isothermal vapor phase epitaxy

Isothermal vapor phase epitaxy (ISOVPE) growth of Hg 1− x Cd x Te (MCT) and Hg 1− x (Cd 1− y Zn y ) x Te (MCZT) was carried out on the substrates of CdTe and nearly lattice matched Cd 1− y Zn y Te ( y=0.045, CZT) to HgTe, respectively. The properties of MCZT/CZT epilayers with lattice mismatch and Zn addition were characterized and compared with those of MCT/CdTe epilayers. There is no obvious difference in electrical properties between MCT and MCZT epilayers. The hardness of MCZT is significantly greater than that of MCT. This is a good indication of the stability of the MCZT. Full width at half maximum (FWHM) of a four crystal X-ray rocking curves for the lattice matched MCZT/CZT is extremely smaller than that of the MCT/CdTe and the smallest FWHM value 36 arcsec, which is comparable to those reported by the other epitaxial methods.

A novel multi-heterojunction HgCdTe long-wavelength infrared photovoltaic detector for operation under reduced cooling conditions

A new multi-heterojunction photovoltaic infrared photodetector is presented. The device has been developed specifically for operation at elevated temperatures for detection of infrared radiation in the mid- and long-wavelength range of the infrared spectrum. The new structure solves the perennial problems of poor quantum efficiency and low dynamic resistance found in conventional long-wavelength infrared photovoltaic detectors when operated near room temperature. Analysis indicates that practical devices with properly optimized multiple heterojunction layers are capable of achieving the performance limits imposed by the statistical nature of thermal generation-recombination processes. In order to demonstrate the technology, multiple heterojunction devices have been fabricated on epilayers grown by isothermal vapour phase epitaxy of HgCdTe and in situ As p-type doping. The detector structures were formed using a combination of conventional dry etching, angled ion milling and angled thermal evaporation for contact metal deposition. These multi-junction HgCdTe heterostructure devices exhibit performances comparable to, or better than, existing long-wavelength photoconductors and photoelectromagnetic detectors operated under the same conditions. A typical of optically immersed multiple heterostructure photovoltaic detectors of approximately can be achieved at a signal wavelength of and for operation at 230 K.

Growth Kinetics of Hg1-xCdxTe Epilayers by Semiclosed Open-Tube Isothermal Vapor Phase Epitaxy

Hg1-xCdxTe (MCT) epilayers were grown on (110) CdTe substrates by semiclosed open-tube isothermal vapor phase epitaxy (ISOVPE). The effects of growth parameters on the surface compositions (x) and thicknesses of the epilayers have been clarified and discussed using the general ISOVPE model. It is found that the growth is limited by the interdiffusion process. The growth kinetics in the interdiffusion control regime was also studied. The growth rate followed the t1/2 dependence expected for interdiffusion-limited processes, and the growth rate constant (A) is given by the Arrhenius form with A0=6.63×10-2 cm2/s and the activation energy Q=1.33 eV. The interdiffusion coefficients for the composition (0.05<x<0.5) and temperature (698 K≤T≤ 773 K) are expressed as D(cm2/s)=550exp (-9.27 x)exp (-1.95 eV/κT) by Fleming-Stevenson analysis.

Effect of CdTe Layer Thickness on Hg1-xCdxTe Epilayer Growth by Isothermal Vapor Phase Epitaxy Using (100) CdTe/GaAs Substrates and Void Formation at the Interface

The growth of Hg1-xCdxTe (MCT) epilayers by isothermal vapor phase epitaxy (ISOVPE) on (100) CdTe/GaAs substrates, with various thicknesses of CdTe layers, is reported. Subsequent to ISOVPE growth of MCT layer, we observed the formation of triangular voids at the interface between CdTe and GaAs, which strongly depends on the thickness of the CdTe substrate layers. The problem of void formation and Ga outdiffusion can be overcome by using a sufficiently thick CdTe layer. Although the crystallinity of CdTe layers grown on GaAs by hot wall epitaxy (HWE) is strongly related to thickness, the quality of MCT epilayers is better than that of the substrate layer and is independent of the quality of CdTe layers. This result is attributed to the growth mechanism of ISOVPE being different from other epitaxial methods.

Multi-heterojunction large area HgCdTe long wavelength infrared photovoltaic detector for operation at near room temperatures

This paper describes a new multi-heterojunction n+pp photovoltaic infrared photodetector. The device has been developed specifically for operation at temperatures of 200–300K in the long wavelength (8–14 µm) range of the infrared spectrum. The new structure solves the perennial problems of poor quantum efficiency and low dynamic resistance found in conventional long wavelength infrared photovoltaic detectors when operated near room temperature. Computer simulations show that devices with properly optimized multiple heterojunctions are capable of achieving the performance limits imposed by the statistical nature of thermal generation-recombination processes. In order to demonstrate the technology, multiple heterojunction devices have been fabricated on epilayers grown by isothermal vapor phase epitaxy of HgCdTe and in situ As p-type doping. The detector structures were formed using a combination of conventional dry etching, angled ion milling, and angled thermal evaporation for contact metal deposition. These multi-junction n+pp HgCdTe heterostructure devices exhibit performances which make them useful for many applications. D* of optically immersed multiple heterostructure photovoltaic detectors exceeding 108cmHz1/2/W were measured at λ=10.6 µm and T=300K.