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The effect of irradiation with different doses of 4-MeV electrons on radiative recombination of nonequilibrium charge carriers in Cu(In,Ga)(S,Se)2 thin films of solar cells was studied. Near-edge photoluminescence (PL) in the energy range ~0.9–1.2 eV in nonirradiated and irradiated direct-gap Cu(In,Ga)(S,Se)2 solid solutions was caused by optical interband transitions and radiative recombination through energy levels of acceptor- and donor-type structure defects in the presence of strong potential fluctuations. PL spectra measured in the temperature range 5–300 K exhibited energy shifts of the near-edge PL band maxima and redistributions of their intensities in thin films after irradiation with different doses of electrons. The activation energies of nonradiative recombination were determined from the quenching of PL band intensities. The possible nature of structural defects in nonirradiated and electron-irradiated Cu(In,Ga)(S,Se)2 solid solutions was discussed. [ABSTRACT FROM AUTHOR]

Resonances of free excitons at energies A ~ 1.0409 eV, B ~ 1.0445 eV, and C ~ 1.2690 eV were detected in reflection spectra of single crystals of the direct-gap compound CuInSe2 at a temperature of 8.6 K. The appearance of the three reflection resonances A, B, and C could be explained by removal of degeneracy from valence-band energy levels due to the influence of crystal field and spin–orbit interaction on the tetragonal lattice of CuInSe2 with ΔCF ~ 5.4 meV and ΔSO ~ 224 meV. Measurements of the temperature dependence of the reflection spectra in the range 8.6–90 K showed the energies of free-exciton resonances A and B increased because of deformation of the unit cell (tetragonal stretching) of the CuInSe2 lattice with the chalcopyrite structure. The binding energies of free excitons A and B were determined as 10.7 and 152 meV based on temperature quenching of exciton resonances A ~ 1.0409 eV and B ~ 1.0445 eV [ABSTRACT FROM AUTHOR]

Multilayer mercury–cadmium–telluride photodetecting heterostructures grown by molecular beam epitaxy on Si and GaAs substrates were studied using the infrared photoreflectance method. Based on the period of Franz–Keldysh oscillations observed in the photoreflectance spectra, the strength of the built-in electric field near the "working layer—graded band gap near-surface layer" heterointerface was determined in a contactless way. An analytical calculation of distribution of such field over the structure depth has specified the region in which the photomodulation signal is formed. The experimentally obtained field values turned out to be higher than the calculated ones, which is explained by the influence of the photovoltaic effect. [ABSTRACT FROM AUTHOR]

In this work, the spectra of optical constants of epitaxial layers of cadmium telluride near the fundamental absorption edge are studied. For this purpose, ellipsometric measurements of the layers under study were carried out in a vacuum chamber in the temperature range from T = 38–275°C. A numerical algorithm has been developed for solving the inverse ellipsometry problem for the structures under consideration, with the help of which the spectral dependences of the refractive index n(λ) and absorption index k(λ) are determined in the wavelength range from 700 to 1000 nm. The parametric dependences of k(λ, T) in the fundamental absorption region and in the transparency region are presented. The presence of an extended absorption tail in the transparency region was established, presumably associated with imperfections in the crystal structure. [ABSTRACT FROM AUTHOR]

The results of photoluminescence (PL) study of As-doped Cd0.3Hg0.7Te solid solutions layers grown by molecular beam epitaxy on a Si substrate are presented. Analysis of the PL spectra obtained at different temperatures and excitation laser powers allows one to judge the nature of the observed peaks. The activation of arsenic in annealed samples was established, as a result of which small acceptor levels are formed. The effectiveness of arsenic as an acceptor impurity for cadmium-mercury tellurides has been confirmed. [ABSTRACT FROM AUTHOR]

The results of a study of photoluminescence (PL) of epitaxial films of Hg0.3Cd0.7Te and Hg0.7Cd0.3Te solid solutions grown by molecular beam epitaxy are presented. A comparison of PL data with the results of optical transmission measurements and structural and microscopic studies showed that in terms of the degree of disorder of the solid solution, the studied Hg0.7Cd0.3Te films are not inferior in quality to the material synthesized by other methods. For Hg0.3Cd0.7Te films, PL data revealed significant composition fluctuations and the presence of acceptor states, which indicates the need to optimize the technology. [ABSTRACT FROM AUTHOR]

The problems of in situ ellipsometric control during the growth of ZnTe and CdTe buffer layers intended for cadmium-mercury-tellurium epitaxy are considered. It has been established that for 20 nm ZnTe layers the spectral dependences of the optical constants near the absorption edge are smoothed, which indicates the presence of structural defects in the film. It has been shown that the microrelief of the CdTe growth surface is a criterion for the structural perfection of the layers and can be measured using an ellipsometer both at the early stages and during steady-state growth. [ABSTRACT FROM AUTHOR]

The paper presents the results of studying the dark currents of nB(SL)n structures with a superlattice (SL) in the barrier region based on Hg1 – xCdxTe grown by molecular beam epitaxy (MBE) in a wide range of experimental conditions. Dark currents were measured in the temperature range from 11 to 300 K for mesa structures with different cross-sectional diameters. The temperature dependences of the bulk component of the dark current density and the surface leakage current density are determined. It is shown that in the studied structures the current-voltage characteristics (CVCs) are formed by both the bulk and surface components of the current depending on the temperature and bias voltage. [ABSTRACT FROM AUTHOR]

This study is devoted to the study of metal–insulator–semiconductor (MIS) structures based on n-HgCdTe (MCT) grown by molecular beam epitaxy (MBE) in the NBνN configuration, intended for the development of infrared (IR) detectors with reduced dark currents for MWIR and LWIR spectral ranges. Seven types of MIS structures have been studied by the admittance spectroscopy method. It is shown that the measurements of the frequency dependences of the impedance of MIS devices make it possible to accurately determine the differential resistance of the barrier structure. It has been established that for one of the studied structures, the values of the differential resistance are determined by the bulk component of the dark current, while the surface leakage component does not significantly affect the measured impedance. It is shown that if the problem of passivation of mesa structures is solved, it is possible to fabricate efficient MWIR and LWIR nBn, NBνN detectors based on MBE HgCdTe with high threshold parameters. [ABSTRACT FROM AUTHOR]

The study is devoted to an experimental analysis of the electrical and photoelectric characteristics of barrier photosensitive structures in the NBνN configuration based on n-HgCdTe. Seven different types of photosensitive structures for MWIR and LWIR infrared ranges, grown by molecular beam epitaxy, have been studied. The current–voltage characteristics were measured both in the dark and under illumination. The parameters of the NBνN structure, which realizes the maximum values of the photocurrent and the minimum values of dark currents in the operating range of bias voltages V for elevated operating temperatures, are determined. [ABSTRACT FROM AUTHOR]

Chemical pretreatment and surface cleaning is a key procedure of semiconductor technologies. Development of methods for the preparation of mercury cadmium telluride (HgCdTe) surfaces is of interest because this material has a wide range of known and potential applications in photoelectronics. This work reports an XPS and AFM study of the effect of various chemical treatments on the chemical composition and micro-morphology of the HgCdTe surface. Among all considered etchants, only ammonium hydroxide effectively removes the native oxide of HgCdTe without leaving a surface layer of metallic tellurium, while preserving nearly stoichiometric chemical composition of the surface. The optimal time of aqueous ammonia treatment is determined. [ABSTRACT FROM AUTHOR]

Dark currents in medium-wave nBn structures based on HgCdTe grown with the aid of molecular beam epitaxy on the (013) GaAs substrates are studied. The passivation of the surface of the side walls of the mesastructures is performed using Al2O3 films formed by plasma atomic layer deposition. It is shown that the volume component of the dark current dominates in the nBn structures with a composition in the barrier layer of 0.84. The activation energy of the current is close to the band gap of the absorbing layer. Comparison of the experimental results with the results of the Rule07 empirical model shows that the diffusion limitation of the dark current takes place in the fabricated structures in a temperature interval of 180–300 K. The results indicate that the molecular beam epitaxy of HgCdTe on alternative substrates is a promising method for fabrication of unipolar barrier detectors for a spectral interval of 3–5 µm. [ABSTRACT FROM AUTHOR]

Bright–field and high-resolution transmission electron microscopy were used for nano-scale structural studies of defects induced by implantation of arsenic ions with 190 keV energy and 1014 cm–2 fluence in n and p-type Hg0.78Cd0.22Te films grown by molecular-beam epitaxy. A similarity in defect pattern formed by arsenic implantation in n and p-type material was observed. The electrical properties of the implanted layers in n and p-type films also appeared to be similar, confirming the results of microscopic observations. [ABSTRACT FROM AUTHOR]

Mid- and long-wave infrared nBn structures based on HgCdTe grown by molecular beam epitaxy (MBE) on GaAs (013) substrates were fabricated. For mid-wave nBn structures, the composition in the absorbing layer was 0.29, and for long-wave nBn structures, this composition was 0.21. The composition in the MBE HgCdTe barrier layers ranged from 0.61 to 0.67. Based on the fabricated HgCdTe nBn structures, test metal–insulator–semiconductor (MIS) devices were created by applying a dielectric Al2O3 film with the thickness of about 90 nm. The admittance of test MIS devices was investigated over a wide range of frequencies and temperatures. An equivalent circuit of MIS device based on MBE HgCdTe nBn structure is proposed, which includes the dielectric capacitance, the capacitance and resistance of the barrier layer, and the series resistance of the absorbing layer bulk. It is shown that the values of the equivalent circuit elements are easy to determine from the experimental frequency dependences of admittance in accumulation mode. Comparison of element values for MIS devices based on mid-wave and long-wave nBn structures is carried out. [ABSTRACT FROM AUTHOR]

The admittance of test MIS structures based on nBn systems from Hg1 –xCdxTe grown by molecular beam epitaxy is investigated. Composition x in the absorbing and contact layers is 0.29; in the barrier layer, it is 0.60. An equivalent circuit of an MIS-structure based on an nBn system is proposed and the nominal values of the elements of this circuit are found under various conditions. Comparison of the temperature dependence of the barrier resistance with the Rule07 model indicates the possibility of creating efficient nBn detectors based on HgCdTe grown by molecular beam epitaxy for the 3- to 5-μm spectral range. [ABSTRACT FROM AUTHOR]

Two types of long-wave infrared nBn-structures based on mercury cadmium telluride grown by molecular beam epitaxy on GaAs (013) substrates have been fabricated. For each type of device, the side walls of the mesa structures were passivated with an Al2O3 insulating film or left without passivation. The CdTe content in the absorbing layers was 0.20 and 0.21, and in the barrier layers, it was 0.61 and 0.63. The dark currents of the manufactured devices were studied in a wide range of voltages and temperatures. The values of the surface leakage component are found under various conditions. It has been shown that the surface leakage current density decreases upon passivation with an Al2O3 film. It was found that in the fabricated nBn-structures at room temperature, the surface leakage component dominates at reverse biases, and at forward biases, the dark current is determined by the combined effect of the surface leakage component and the bulk current component. From the Arrhenius plots, the values of the activation energies of the surface leakage current component were found, which are in the range from 0.05 to 0.10 eV at small reverse biases. At small reverse biases, upon cooling the samples, the role of the bulk component of the dark current increases, which at 180 K is approximately 0.81 A/cm2. In the temperature range 200–300 K, the values of the dark current density exceed the values calculated according to the empirical Rule07 model by a factor of 10-100, which indicates the possibility of creating the long-wave infrared barrier detectors by decreasing the values of the surface leakage component. [ABSTRACT FROM AUTHOR]

The problem of in situ temperature control during the growth of epitaxial layers of HgCdTe by molecular beam epitaxy is considered. Various approaches to solving the problem using spectroscopic ellipsometry are proposed. They are based on the temperature dependence of the optical constants spectra of the CdTe buffer layer and the growing HgCdTe layer. The results of experimental testing of these methods are presented, which show that the temperature measurement accuracy is several degrees, and the sensitivity reaches fractions of a degree. At the stage of stationary growth, it is possible to determine the change not only in the temperature, but also in the composition of the growing layer from the ellipsometric spectra. [ABSTRACT FROM AUTHOR]

Mid-wave infrared nBn structures based on HgCdTe grown by molecular beam epitaxy on GaAs (013) substrates were fabricated. The composition in the absorbing layer was 0.29, and in the barrier layer it was 0.67. It was shown that the dark currents of the created nBn structures are limited by the surface leakage component. To study the bulk component of the dark current, it was proposed to use the admittance measurements of test metal-insulator-semiconductor (MIS) devices based on fabricated nBn structures in the case of the formation of a backward contact to the absorbing layer. It was established that surface leakage does not affect the dynamic resistance of the MIS device barrier. The dependence of the dynamic resistance of the barrier layer (Rb) of the MIS device in the accumulation mode on the area of the front electrode (A), voltage, and temperature was determined. It was shown that, with the exclusion of surface leakage, the values of the RbA product in a temperature range of 230–300 K at forward biases are determined by the diffusion current of holes from the contact layer, and at reverse biases, by the diffusion current from the absorbing layer. It was found that at temperatures of 210–300 K, RbA values exceeding the values of this parameter determined according to the empirical model Rule 07 were realized in the fabricated structures. [ABSTRACT FROM AUTHOR]

Accumulation of arsenic implantation-induced donor defects in heteroepitaxial Hg1−xCdxTe structures with the composition of the active layer xa = 0.30 was studied with the use of the Hall-effect measurements and mobility spectrum analysis. The studies allowed for identifying the carriers in the implantation-damaged n+-layer, namely, electrons with low and intermediate mobility, and for establishing the dependence of their concentration on the ion fluence. The electrically active implantation-induced defects in the studied structures, similar to the case of those with xa = 0.22, were identified as atoms of interstitial mercury captured by dislocation loops and quasi-point defects. In the material with xa = 0.30, a weak dependence of the concentration of low-mobility electrons on the fluence was observed. In general, a substantial difference in the properties of p+–n junctions formed as a result of arsenic implantation in the structures with xa = 0.30 and xa = 0.22 was established. The difference was explained by the effect of the graded-gap surface layer on the diffusion of charged defects released during the implantation. [ABSTRACT FROM AUTHOR]

The effect of As+ ion implantation on the electrical properties of the near-surface layer of n-HgCdTe films grown by molecular beam epitaxy (MBE) on Si (310) substrates was experimentally studied. A specific feature of MBE n-Hg0.78Cd0.22Te films is the presence of near-surface graded-gap layers with a high CdTe content, formed during epitaxial growth. The properties of as-grown films and films after As+ ion implantation with ion energy of 200 keV and fluence of 1014 cm−2 were studied. Post-implantation activation annealing was not performed. Test metal–insulator–semiconductor (MIS) structures were created based on as-grown and as-implanted samples by plasma-enhanced atomic layer deposition of Al2O3 insulator films. The admittance of the fabricated MIS structures was measured over a wide range of frequencies and temperatures. When determining the parameters of MIS structures, we used techniques that take into account the presence of near-surface graded-gap layers and series resistance of the HgCdTe film bulk, as well as the high density of slow surface states. It was found that, in as-implanted samples, the donor center concentration in the near-surface layer exceeds 1017 cm−3 and increases with distance from the HgCdTe-Al2O3 interface (at least up to 90 nm). After implantation, the conductivity of MBE HgCdTe film bulk increases markedly. It was shown that, for as-implanted samples, the generation rate of minority charge carriers in the MBE HgCdTe surface layer is significantly reduced, which indicates the appearance of a low defect layer with a thickness of at least 90 nm. [ABSTRACT FROM AUTHOR]

The phase composition and structural and optical characteristics of thin films of Cu(In1–xGax)(SySe1–y)2 solid solutions with the chalcopyrite structure were investigated. The unit-cell constants according to x-ray diffraction analysis were a ~ 5.720 Å and c ~ 11.52 Å. The elemental compositions were x = Ga/(Ga + In) ~ 0.14 and y = S/(S + Se) ~ 0.11 for Cu(In1–xGax)(S ySe1–y)2 thin films. The optical band gap of Cu(In1–xGax)(S ySe1–y)2 solid solutions determined from measurements of photoluminescence spectra and luminescence excitation spectra at ~4.2 K was Eg ~ 1.122 eV. The mechanism of radiative recombination of nonequilibrium charge carriers in thin films of Cu(In1–xGax) (S ySe1–y)2 solid solutions is discussed. [ABSTRACT FROM AUTHOR]

Mercury cadmium telluride n-Hg1 –xCdxTe (HgCdTe) films with near-surface wide-bangap layers were grown by molecular beam epitaxy on Si(013) substrates. Admittance of the metal–insulator–semiconductor (MIS) structure was measured in samples based on the initial HgCdTe film and the same films after implantation with As+ ions and after subsequent thermal annealing. Methods taking into account the presence of near-surface graded-gap layers and slow surface states were used to determine the main parameters of these layers upon technological procedures involved in the production of photodiodes. [ABSTRACT FROM AUTHOR]

Radiation-induced effects in Cu(In,Ga)Se2 alloy thin films after implantation with hydrogen ions with energies of 2.5, 5, and 10 keV and a dose of ~3 × 1015 cm–2 are studied. Comparative analysis of the optical characteristics of nonimplanted and hydrogen-implanted Cu(In,Ga)Se2 films is conducted on the basis of photoluminescence spectra and luminescence-excitation spectra recorded at liquid-helium temperature (~4.2 K). The band gap determined for Cu(In,Ga)Se2 alloys by mathematical processing of the luminescence-excitation spectra is ~1.171 eV. In the photoluminescence spectra of nonimplanted and hydrogen-implanted Cu(In,Ga)Se2 films, an intense band is detected, with a maximum at ~1.089 eV. The band is defined by the recombination of free electrons with holes localized in the valence-band tails. It is established that broad bands with maximums at the energies 0.92 and ~0.77 eV are defined by the radiative recombination of nonequilibrium charge carriers at deep energy levels of ion-induced acceptor defects formed in the band gap of Cu(In,Ga)Se2 alloys. The conditions for the effect of the ion passivation of dangling electron bonds at the surface and in the bulk of polycrystalline Cu(In,Ga)Se2 films and the nature of structural point defects and the mechanisms of radiative recombination are discussed. [ABSTRACT FROM AUTHOR]

Based on in situ and ex situ ellipsometric measurements, the spectral dependences of the temperature sensitivity of the optical constants Hg1 –xCdхTe—dn(λ) and dk(λ) have been found for a series of samples of different compositions in the range from 0.160 to 0.327. The experiments were performed during cooling of the grown samples in a vacuum chamber. It has been found that the obtained dn and dk dependences can be well approximated by the sum of three Lorentz oscillators with the addition of the dispersion terms of the Cauchy formula. A parametric model that describes the sensitivities dn(λ) and dk(λ) for an arbitrary composition x in the specified range near the growth temperature has been proposed. Ex situ temperature measurements performed near room temperature correlate with the data of the high-temperature measurements. The results obtained are relevant for the development of ellipsometric control methods in situ of Hg1 –xCdхTe layer growth processes. [ABSTRACT FROM AUTHOR]

The results of studying the optical transmission, photoconductivity, photoluminescence, and X-ray diffraction of HgCdTe solid-solution samples with a high content of CdTe (molar fraction 0.7–0.8), grown by molecular-beam epitaxy (MBE) and liquid-phase epitaxy (LPE), are presented. It is shown that the material under study shows a significant degree of disorder of the solid solution, which is greater in structures grown by MBE on GaAs substrates, compared with the LPE-grown films. A study of the photoluminescence reveals states in the band gap, previously considered untypical of HgCdTe films grown on GaAs substrates, but typical only of films grown on Si. On the whole, the high quality of the material with a high CdTe content, grown by MBE and used to create the HgTe/HgCdTe nanostructures currently in high demand, is confirmed. [ABSTRACT FROM AUTHOR]

A parametric model describing the spectra of optical constants n(λ) and k(λ) of a Hg1 –xCdxTe (MCT) solid solution for the x values in the range from 0.2 to 0.4 is developed. This model is based on empirical data measured in situ during the epitaxial growth of solid-solution layers. Several versions of application of the obtained model for in situ real-time determination of the MCT composition have been considered. A technique for determining the composition using spectral ellipsometric measurements is proposed, which ensures the error of no more than δx = ±0.0035. [ABSTRACT FROM AUTHOR]

Optical reflectance and bright-field and high-resolution transmission electron microscopy studies of radiation damage induced by implantation of arsenic ions with 190 keV and 350 keV energy and 1014 cm–2 fluence in molecular-beam epitaxy-grown Hg0.7Cd0.3Te films were performed. A similarity in defect pattern formed by arsenic implantation in Hg1−xCdxTe with x ≈ 0.2 and x ≈ 0.3 straight after the implantation was observed with formation of three nano-size defect layers containing dislocation loops of vacancy- and interstitial-types, single dislocations and lattice deformations. After post-implantation arsenic activation annealing, most of these defects in our Hg0.7Cd0.3Te films, in contrast to Hg0.8Cd0.2Te films, disappeared. This effect is explained by the reduced influence of the electric field of the graded-gap surface layer on the diffusion of charged point defects under annealing. [ABSTRACT FROM AUTHOR]

Three types of nBn structures based on mercury cadmium telluride grown by molecular beam epitaxy have been fabricated. As barrier layers in nBn structures, Hg1–xCdxTe at x = 0.67 and 0.84 and the 18 period Hg0.20Cd0.80Te (9 nm) – HgTe (2 nm) superlattice were used. To study the properties of barrier layers based on nBn structures, MIS devices were created using dielectric Al2O3 films. The impedance of the created devices was investigated over wide ranges of voltages, frequencies, and temperatures. Equivalent circuits of MIS devices based on nBn structures in the accumulation mode are proposed. It is shown that measurements of the frequency dependences of the impedance make it possible to determine the values of the differential resistance of the barrier layer in a wide range of conditions. It was found that the values of the differential resistance are determined only by the bulk component of the dark current, and the surface leakage component does not affect the measured impedance of MIS devices. The dependences of the values of the equivalent circuit elements on the area of structures, voltage, and temperature are determined. It is shown that in the temperature range 210–300 K, the values of the differential resistance of the barrier layer based on Hg0.33Cd0.67Te are determined by the diffusion-limited flow of holes from the contact and absorbing layers, at the forward and reverse biases, respectively. The values of the product of the differential resistance and the area are determined for nBn structures with various parameters of the barrier layers. The possibilities of using the measurements of impedance of MIS devices based on nBn structures to study the homogeneity of properties of various layers are demonstrated.. [ABSTRACT FROM AUTHOR]

The emission spectra of thin nanocrystalline films of Cu(In1 –xGax)(SySe1 –y)2 (CIGSSe) direct-gap solid solutions in the structure of solar cells, recorded upon continuous-wave laser excitation (~0.5 W/cm2) and nanosecond pulsed laser excitation with a power density in the range of 0.1–53 kW/cm2 at temperatures ranging from 10 to 300 K, are analyzed. It is found that stimulated emission (SE) occurs in thin CIGSSe films at temperatures from 10 to 90 K in the spectral range hν = 1.062–1.081 eV, with a minimum threshold-pump level of ~1 kW/cm2. It is shown that the spontaneous emission band is blue-shifted with an increase in the excitation intensity. It is also established that, with an increase in temperature, the photoluminescence (PL) band (upon weak excitation) and the stimulated-emission band are blue-shifted, whereas the PL band is red-shifted upon strong excitation. The possible reasons and mechanisms for the influence of temperature and excitation intensity on the spectral positions of the spontaneous and stimulated emission bands for the solid-solution films are discussed. [ABSTRACT FROM AUTHOR]

We provide a review of the current state, problems and their solutions, and potential possibilities to develop the technology of the Molecular Beam epitaxy (MBE) to obtain CdHgTe structures on various substrates for infrared detectors. We present the data about MBE supervacuum units control tools for growth processes, collected according to used substrates preparation processes for substrate surfaces, growth of buffer layers on alternating substrates, and growth and alloying of CdHgTe layers. We present main defects of structures (such as line defects and macrodefects) and their least achieved concentration levels limiting the quality of detectors. We consider the data about problems of the external alloying of CdHgTe layers by dopants and the obtained electrophysical parameters of such layers. We provide photoelectric parameters of IR-detectors, close to theoretical ones and showing that the MBE technology is ready to produce CdHgTe/Si structures on six-inch diameters. We demonstrate results of the research and development of the growth and alloying of CdHgTe structures on GaAs substrates and Si substrates of 76.2-mm diameters, implemented at the Rzhanov Institute of Semiconductor Physics, Siberian Branch of the Russian Academy of Sciences. [ABSTRACT FROM AUTHOR]

We report an experimental study of the electrical properties of the interface between the Al2O3 passivating coating grown by plasma enhanced atomic layer deposition at different temperatures and the p-CdHgTe (xCdTe = 0.22) coating grown by molecular beam epitaxy via measuring the C–V characteristics of MIS structures. It has been established that, at an Al2O3 growth temperature of 200°C, the concentration of acceptors in CdHgTe increases due to dissociation and, at a temperature of 80°C, the spread of the insulator capacitance and built-in charge increases. The optimum temperature for growing the passivating Al2O3 coating on CdHgTe lies in the range of 120–160°C. [ABSTRACT FROM AUTHOR]

Optical transmission, photoluminescence and photoconductivity were used to study Hg1−xCdxTe with x = 0.7–0.8 (bandgap 0.8–1.1 eV at 300 K) grown by molecular-beam epitaxy. The studied material, which included layers used as spacers and barriers in potential- and quantum-well structures, showed a considerable degree of alloy disorder similar to narrower-bandgap HgCdTe grown by the same method. The observed disorder seemed to have no effect on the structural properties of the material and its optical absorption. Optimization of the growth technology of wider-bandgap HgCdTe should help improve the quality of potential- and quantum-well structures based on this material. [ABSTRACT FROM AUTHOR]

Bright-field and high-resolution transmission electron microscopy and microdiffraction have been used for the study of defects in two HgTe/HgCdTe single quantum well (QW) structures grown by molecular beam epitaxy on GaAs substrates with ZnTe and CdTe buffer layers. Defects in QW layers were identified as stacking faults, dislocations, dislocation loops and lattice deformations. The importance of an extra HgCdTe layer placed between the CdTe buffer and HgTe/HgCdTe QW structure for the reduction of defect density both in the barrier layers and in the well itself was demonstrated. [ABSTRACT FROM AUTHOR]

The results of studying the admittance of unipolar barrier structures based on HgCdTe grown by molecular beam epitaxy (MBE) on GaAs (013) substrates are presented. Using passivation with an Al2O3 insulator, device nBn structures based on HgCdTe were fabricated. The layer parameters in the created structures provided the possibility of detection in the spectral range of 3–5 μm. Based on the analysis of the frequency dependences of the admittance, an equivalent circuit of nBn structures at small biases is proposed. The dependences of the equivalent circuit parameters on the area of the mesa structure and temperature are determined. The properties of high-temperature maxima in the voltage dependences of the capacitance and conductance of nBn structures, which are presumably related to the recharging of surface states at the heterointerface between the barrier and absorbing layers, are studied. It is found that in a wide range of frequencies and temperatures, the capacitance – voltage characteristics of nBn structures based on HgCdTe at reverse biases can be used to determine the concentration of donor impurities in the absorbing layer. It is shown that the admittance of test MIS devices in a mesa configuration, formed on the basis of the MBE HgCdTe nBn structures, is determined by the combined influence of electronic processes in the contact, barrier, and absorbing layers. [ABSTRACT FROM AUTHOR]

By profiling the electrical parameters of the arsenic implanted CdHgTe films, grown by molecular beam epitaxy, and comparing the obtained data with the results of studies performed by secondary ion mass spectroscopy and transmission electron microscopy, the localization and nature of donor defects formed during implantation were determined. It has been shown that such defects are dislocation loops and quasi-point defects that trap interstitial mercury atoms released during implantation. [ABSTRACT FROM AUTHOR]

Heteroepitaxial n-Hg0.78Cd0.22Te films with near-surface graded-gap layers were grown by molecular beam epitaxy and subjected to two-stage thermal annealing in saturated mercury vapor atmosphere. The first stage of annealing was carried out for 2 h at a temperature of 360°C. The second stage was carried out at a temperature of 220°C for 24 h. Similar annealing was carried out after As+ ion implantation to activate the introduced impurity and anneal radiation defects. Based on as-grown and annealed films, metal–insulator–semiconductor (MIS) structures were formed by depositing an Al2O3 dielectric by plasma atomic layer deposition. The admittance of fabricated MIS structures was studied in a wide range of frequencies and temperatures. It was found that after thermal annealing, the properties of the n-HgCdTe surface layer are noticeably changed, which is manifested as a decrease in the density of slow states in the transition layer between the dielectric and the semiconductor, and an increase in the generation of minority charge carriers in the n-HgCdTe near-surface layer. These changes in the properties of n-HgCdTe after thermal annealing are associated with the modification of the defect system of the near-surface layer of the semiconductor and the transition layer between dielectric and semiconductor. No significant changes were detected in the bulk properties of the epitaxial film after thermal annealing. A decrease in the density of states near the interface between HgCdTe and Al2O3 during thermal annealing makes it possible to facilitate the electrical characterization of MIS structures by suppressing hysteresis phenomena. [ABSTRACT FROM AUTHOR]

Matrix photosensitive elements based on a HgCdTe semiconductor solid solution on silicon substrates with 640 × 512 elements at a pitch of 25 μm with a long-wavelength sensitivity of 5 μm at half maximum are designed and produced. The scheme and topology are developed according to which matrix multiplexers with 640 × 512 elements at a pitch of 25 μm, which ensure operating modes at a clock frequency up to 10 MHz, are manufactured. Using a hybrid assembly method on indium bumps, a matrix photodetector with 640 × 512 elements at a pitch of 25 μm is produced. The best photodetector specimens are characterized by the following parameters: average NETD value <13 mK and the number of workable elements > 99.5%. [ABSTRACT FROM AUTHOR]

Abstract—Design and fabrication of photosensitive array elements in the 384 × 288 element format with a step of 25 μm with a long wavelength limit of sensitivity at 0.5 to approximately 9.5 μm were performed. The circuit and topology were developed, according to which matrix high-speed multiplexers are manufactured in the form of 384 × 288 elements with a step of 25 microns, which provide operating modes at a clock frequency of up to 20 MHz. The 384 × 288 element hybrid photodetector (PD) format in 25 μm increments has an average Noise Equivalent Temperature Difference (NETD) of less than 30 mK, while the number of working elements was more than 97%. Examples are given of using the microscanning system to reduce defective pixels in an image frame and/or increase the frame format to 768 × 576. It is shown that as a result of the use of microscans in a thermal imaging channel based on the developed PD during the transition to the 768 × 576 format, an improvement in spatial resolution of 1.4 times was obtained for the same minimum resolved temperature difference (MRTD), while the MRTD at a frequency of 0.44 mrad-1 decreased from 1.6 to 0.9 K compared to the original 384 × 288 format. [ABSTRACT FROM AUTHOR]

Abstract—The characteristics of MWIRs focal plane aeeays made in the form of a hybrid chip based on a planar n+–p-HgCdTe focal matrix with 2048 × 2048 elements and a silicon multiplexer are considered. The temperature dependence of the reverse current of elements in the 125–300 K range had a characteristic Arrhenius dependence with an activation energy close to the band gap of the semiconductor and was limited by the diffusion component of the current. At a lower temperature, the current was limited by the generation of carriers with the participation of a deep level near the middle of the forbidden band. The histogram of the detectability of the elements of the matrix had the form of a symmetric curve with a maximum and an average value ≈ 1.3 × 1012 cm Hz1/2/W. [ABSTRACT FROM AUTHOR]

This paper presents the results of numerical simulation for 4 ¯ 3 m crystals and experimental results for azimuthal angular dependences of polarization components of a second harmonic signal reflected from GaAs(013) substrates, CdTe/ZnTe/GaAs buffer layers, and CdxHg1−xTe/CdTe/ZnTe/GaAs structures, sequentially grown on these substrates with normal incidence of probing laser radiation on the sample and azimuthal rotation of its polarization plane. It is revealed from investigating the GaAs(013) substrates and CdTe/ZnTe/GaAs buffer layers that deviations from the base cut (013) relative to angles θ and ϕ turn out to be 1–3° in the GaAs substrates and up to 8° in the CdTe/ZnTe/GaAs buffer layers. The observed asymmetry of the minima of angular experimental dependences of the second harmonic signal in the GaAs substrates is related to stresses. It is assumed on the basis of the experimental data that the values of the components of the nonlinear susceptibility tensor χxyz(ω) of the crystalline structure CdxHg1−xTe significantly exceed those of similar tensor components in CdTe and GaAs. [ABSTRACT FROM AUTHOR]

Radiation damage and its transformation under annealing were studied with bright-field and high-resolution transmission electron microscopy for arsenic-implanted HgCdTe films with graded-gap surface layers. In addition to typical highly defective layers in as-implanted material, a 50 nm-thick sub-surface layer with very low defect density was observed. The main defects in other layers after implantation were dislocation loops, yet after arsenic activation annealing, the dominating defects were single dislocations. Transport (from depth to surface), transformation and annihilation of radiation-induced defects were observed as a result of annealing, with the depth with the maximum defect density decreasing from 110 to 40 nm. [ABSTRACT FROM AUTHOR]

The disordering in cadmium mercury telluride solid solution films grown by molecular beam epitaxy on Si and GaAs substrates has been examined by optical transmission and photoluminescence investigations. The effect of a fundamental decrease in the disordering scale under thermal annealing and possible interplay of the observed phenomena with defects typical of films grown by molecular beam epitaxy are discussed. [ABSTRACT FROM AUTHOR]

The capacitance–voltage (CV) curves of metal–insulator–semiconductor (MIS) systems based on an HgCdTe nBn structure grown by molecular-beam epitaxy on GaAs(013) substrates were studied for the first time in a wide range of frequencies and temperatures. The electron concentration in the near-surface film layer was determined by capacitive measurements and is close to the indium dopant concentration. It was demonstrated that the CV characteristics of MIS systems have a high-frequency behavior in a wide range of measurement conditions, and the product of the differential resistance of the space-charge region and the electrode area in the strong inversion mode is as high as 40 kΩ cm2. It was found that the capacitance of the MIS system in the accumulation mode decreases after irradiation at 0.91 μm. This effect may be attributed to the transformation of the band diagram of an abrupt heterojunction triggered by changes in the charge state of defects under irradiation. [ABSTRACT FROM AUTHOR]

An ellipsometric procedure developed for noncontact in situ measurement of the CdTe buffer-layer temperature is presented. The procedure is based on the temperature dependence of the energy position of CdTe critical points and is intended for determining the initial temperature of the growth surface before epitaxy of the cadmium–mercury–telluride compound. An express method for determining the position of critical points by the spectra of ellipsometric parameter Ψ is proposed. A series of calibrated experiments is performed. They result in determination of the temperature dependences of the position of critical points. Estimations and the experiment show that the temperature-measurement accuracy is ±3°C. [ABSTRACT FROM AUTHOR]

The admittance of MIS structures based on n(p)-Hg1–xCdxTe (x = 0.21–0.23) grown by molecular-beam epitaxy on Si and GaAs substrates is studied. The possibility of increasing the value of the product of the differential resistance of the space charge region and area of the field electrode RSCRA by creating near-surface graded-gap layers with an increased content of CdTe is investigated. It has been established that the creation of a graded-gap layer leads to an increase in the value of RSCRA by a factor of 10–200 for MIS structures based on n-Hg0.78Cd0.22Te due to suppression of tunneling generation through deep levels and a decrease in the Shockley–Read current. MIS structures based on n-Hg0.78Cd0.22Te without a graded-gap layer grown on GaAs substrates have RSCRA values that exceed 10 or more times the values of the same parameter for structures grown on Si substrates. [ABSTRACT FROM AUTHOR]

Modern designs of time delay and integration (TDI) IR linear scanning focal plane arrays (IR FPAs) are analyzed. Advanced designs of linear IR FPAs with increased sensitivity and spatial resolution are proposed. The analysis is based on Monte-Carlo simulation of the diffusion of photogenerated charge carriers in photodiode arrays based on mercury-cadmium-telluride epitaxial layers taking into account the main photoelectric and design parameters of the detectors and optical system. [ABSTRACT FROM AUTHOR]

Abstract: The stimulated emission of Cu(In,Ga)Se2 alloy thin films formed by magnetron-assisted sputtering onto a sodium-fluoride layer deposited onto a molybdenum layer on a glass substrate is observed. The structural and optical parameters of the films are determined by scanning electron microscopy, local X-ray spectral microanalysis, X-ray structural analysis, and low-temperature luminescence (T = 10 K) measurements in the range of excitation levels of 1.6-75 kW cm-2 provided by nanosecond nitrogen-laser pulses. The stimulated emission threshold corresponds to ~25 kW cm-2. Comparative analysis of the emission of Cu(In,Ga)Se2 thin films suggests that the introduction of sodium results in significant improvement of the structural quality, specifically, in a decrease in the density of energy states in the band tails and in a decrease in the concentration of nonradiative-recombination centers. [ABSTRACT FROM AUTHOR]

Properties of HgCdTe films grown by molecular beam epitaxy on GaAs and Si substrates have been studied by performing variable-temperature photoluminescence (PL) measurements. A substantial difference in defect structure between films grown on GaAs (013) and Si (013) substrates was revealed. HgCdTe/GaAs films were mostly free of defect-related energy levels within the bandgap, which was confirmed by PL and carrier lifetime measurements. By contrast, the properties of HgCdTe/Si films are affected by uncontrolled point defects. These could not be always associated with typical “intrinsic” HgCdTe defects, such as mercury vacancies, so consideration of other defects, possibly inherent in HgCdTe/Si structures, was required. The post-growth annealing was found to have a positive effect on the defect structure by reducing the full-widths at half-maximum of excitonic PL lines for both types of films and lowering the concentration of defects specific to HgCdTe/Si. [ABSTRACT FROM AUTHOR]

Angle-resolved photoemission spectroscopy (ARPES) has been used to study the electronic structure of InSe and CuIn5Se8 single crystals and determine the general patterns of its transformation after the introduction of copper. The main dispersion curves of valence bands in the studied multicomponent systems and the effective masses of majority carriers in CuIn5Se8 have been obtained. Joint theoretical and experimental research has allowed us to apply ARPES not only to single isolated states, but also to complex crystals with a large number of atoms in the unit cell (and, consequently, a large number of dispersion bands). It has been demonstrated that the neighborhoods of maxima and minima of dispersion curves E(k), which essentially define the set of experimental ARPES spectra, make the dominant contribution to the observed signal intensity. [ABSTRACT FROM AUTHOR]