Far infrared reflection spectra due to lattice and free carrier in ZnxHg1−xSe

Far infrared reflection spectra of Zn_xHg_1−xSe with x = 0 to 0.4 showed characteristic of two TO-phonon modes behavior and the plasmon-LO phonon coupling in the region from 20 to 500 cm⁻¹ at 5 and 300 K. The composition dependence of TO modes on the frequency is linear for the HgSe-like mode TO₁ and constant for the ZnSe-like mode TO₂. The additional TO mode due to clustering effect is observed at 113 cm⁻¹. The plasmon-LO phonon coupled modes are explained well by our model taken into account the two-mode behavior and the contribution of interband transitions in dynamic dielectric function.     

Electrical properties of infrared photovoltaic CdxHg1−xTe detectors

p-n junctions in epitaxial graded-gap Cd_xHg_1−xTe layers were produced by the Hg-diffusion method, with molar compositions x from 0.18 to 1. Current-voltage, differential resistivity and capacity characteristics were measured as function of bias in the temperature range 4.2–300 K. Carrier transport mechanisms are discussed, including both generation-recombination and tunnelling processes in the junction. The dependence of electric and photoelectric properties of p-n junctions on both the physical and technological parameters of epitaxial Cd_xHg₁−xTe layers are also analysed.     

Far infrared absorption studies of high Tc superconducting material YBa2Cu3O7−x

The high Tc superconducting material YBa₂Cu₃O_7−x has been studied for its absorption in the FIR region. Measurements have been carried out using a Fourier Transform Infrared (FTIR) spectrophotometer at different temperatures above and below Tc. Observed bands are examined in the light of theoretical calculations based on different models. Certain IR absorption bands show screening effects in the measurements below Tc. Experimental values for observed IR bands are compared with the work of other authors and the bands are assigned to different IR active modes of vibration of the material.     

Photoelectromagnetic effect in CdxHg1−xTe graded-gap structures

Numerical calculations of voltage responsivity of PEM detectors made of graded-gap Cd_xHg_1−xTe structures have been carried out. The model involves a generalized approach, taking into account the x-value and wavelength-dependent material parameters, absorption coefficient and band-to-band recombination time—including Auger-1, Auger-7 and radiative mechanisms.     

Temperature dependence of the electron effective mass in MnxHg1−xSe

We have investigated the temperature dependence of the electron effective mass in Mn_xHg_1–xSe crystals (0 < x 0.1) in the T=90–300 K temperature range. We have determined that the temperature-dependent changes in the band gap (_g), in the band diagram nonparabolicity, and in the conduction band carrier concentration have a strong effect on the temperature dependence of the carrier effective mass at the Fermi level m ^*=f(T).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 11, pp. 5–9, November, 1987.     

Characteristics of pulse plated CdxZn1−xSe films

Cd_xZn_1−xSe films (0 ⩽ x ⩽ 1) were deposited for the first time by the pulse plating technique at different duty cycles in the range 6–50% at room temperature from an aqueous bath containing zinc sulphate, cadmium sulphate and selenium oxide. To the author’s knowledge this is the first report on pulse plated Cd_xZn_1−xSe films. The deposition potential was −0.9 V (SCE). The as deposited films exhibited cubic structure. Composition of the films was estimated by Energy Dispersive Analysis of X-ray studies. X-ray photoelectron spectroscopy studies indicated the binding energies corresponding to Zn(2p_3/2), Cd(3d_5/2 and 3d_3/2) and Se(3d_5/2 and 3d_3/2). Optical band gap of the films varied from 1.72 to 2.70 eV as the composition varied from CdSe to ZnSe side. Atomic force microscopy studies indicated grain size in the range of 20–150 nm.     

Magnetic susceptibility studies of Zn1−xFexSe and Zn1−xFexS

The magnetic susceptibility of diluted magnetic semiconductors Zn_1−xFe_xSe and Zn_1−xFe_xS has been calculated within a crystal field model and by applying the extended nearest-neighbour pair approximation. The results are compared with available experimental data. It appears that a good agreement between theory and experiment is obtained for Zn_1−xFe_xSe taking the long-range exchange comprising several nearer interionic distances, whereas in Zn_1−xFe_xS the exchange interaction with nearest-neighbours alone gives a better solution.     

Intrinsic carrier concentration in Hg1−xCdxTe

The effective mass of heavy holes has been determined on the basis of simultaneous analysis of the Hall coefficient and conductivity data obtained in the temperature region 100–300 K on well characterized p-type Hg_1–x Cd_xTe (x0·2) samples. Its value is 0·7m₀. The calculation of intrinsic carrier concentration for 0·19 x0·3 and 50 Kg T 300 K has been carried out using the above value of the effective mass of holes, Hansen's expression for the band gap and momentum matrix element from magneto-optical measurements.     

Damage and lattice location studies in Hg implanted Hg1–xCdxTe

Abstract

Rutherford backscattering (RBS) and ion induced X-ray (PIXE) channeling experiments have been used to study the damage accompanying Hg and Al implantations into Hg_0.8Cd_0.2 Te and its annealing as well as to determine the location of Hg in the crystal.

The damage induced by the implantation of 300 keV Hg and 250 keV Al ions at room temperature was found from RBS channeling studies to reach a saturation level at doses of 1 × 10¹⁴ cm^?2 and 3 × 10¹⁴ cm^?2 respectively. The damage resembles that characteristic for extended defects and it anneals at ≈ 300°C.

The location of the constituents of Hg implanted Hg_0.8 Cd_0.2 Te was studied by PIXE channeling observing the characteristic X-rays for each element. Angular scans indicate that the channels are mostly blocked by Hg atoms for both unannealed and, to a lesser extent, annealed crystals. This observation supports the suggestion that interstitial Hg atoms may be responsible for the conductivity of Hg implanted Hg_1–x Cd_g Te.     

Excess currents in narrow gap CdxHg1−xTe p-n junctions

Reverse bias dark currents in p-n junctions fabricated in undoped Cd_xHg_1−xTe (CMT) (0.22 < x < 0.24) LPE epilayers by ion implantation of boron have been studied at different temperatures. The behaviour of current-voltage (I–V) characteristics at temperatures below 80 K allows us to discriminate two types of material. The first group consists of samples with currents dominated by a band-to-band tunnelling mechanism. The second is characterized by the current which exceeds that in the first group. The excess currents proved to be connected with fluctuations of charged impurity density which changed local tunnel transparency of the potential barriers. This mechanism is likely to dominate current in closely compensated samples. A quantitative analysis of I–V characteristics is made.     

Spectral Properties of CuGaxIn1−xSe2 Solid Solutions

We have investigated the absorption spectra in the region of the fundamental absorption band edge and the photoluminescence spectra of single crystals of the ternary compounds CuInSe₂ and CuGaS₂, and of solid solutions based on them that were grown by the method of chemical transport reaction. The forbidden band width and the positions of the maxima of the radiation bands are determined. The concentration dependences of the indicated quantities are plotted and they are shown to be linear.     

Structural,electrical and optical properties of Cdx Zn1−xSe thin films

X-ray diffraction and electron diffraction techniques indicate that Cd_x Zn_1–xSe thin films on glass substrates have a polycrystalline nature, with sphalerite structure for x0.5 and wurtzite structure for x0.6. The crystalline size in each composition increases with increasing the film thickness. The room temperature dark resistivity varies from one composition to another showing a transition at x=0.55The temperature dependence of of the deposited films revealed two conduction mechanisms, one below 352 K due to shallow levels, surface states, and defects introduced during the film growth, and over 352 K due to deep-level ionization following the ordinary semiconducting behaviour.The thermal activation energy of the free charge carriers decreases linearly with increasing the molar fraction x of the CdSe content up to x=0.55, above which it increases with increasing x.The optical constants of Cd_x Zn_1–xSe thin films of different compositions were determined in the spectral range 400–2000 nm. The analysis of the absorption coefticient at and near the absorption edge indicates the existence of allowed direct transition energy gaps decreasing with increasing x.     

Effect of temperature on the band structure of MnxHg1−xSe

The band structure of the solid solutions Mn_xHg_1–xSe is constructed on the basis of the band parameters obtained from the electrophysical and optical investigations of these solid solutions. It is shown that the band structure of Mn_xHg_1–xSe and the dynamics of the bands as a function of the composition and temperature are analogous to those for Cd_xHg_1–xTe. It is shown that the variation of the nonparabolicity of the band spectrum of Mn_xHg_1–xSe as a function of the temperature greatly affects the temperature coefficient of the change of the width of the optical forbidden band (d_gop/dT).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 40–44, April, 1991.     

Galvanomagnetic infrared-luminescence of varying-gap CdxHg1−xTe/CdTe structures

Luminescence of varying-gap epitaxial Cd_xHg_1−xTe films at T = 295 K under conditions of magnetoconcentration effect were investigated theoretically and experimentally. Field and spectral characteristics of the positive and negative luminescence were studied. The use of varying-gap structures in combination with the magnetoconcentration effect for the excitation of luminescence in narrow-gap semiconductors at high temperatures is shown to be promising. In this case, high radiation power and the possibility of controlling the luminescence spectrum are demonstrated.     

Analysis of infrared thermoreflectance spectra of NbxTi1−xS2

Thermoreflectance spectra of Nb_xTi_1−xS₂ crystals in the infrared are reported and discussed. In particular the plasmon lineshape, an interband transition at ≅0.8 eV and the effect of cation substitution on infrared thermoreflectance spectra are examined.     

Nonlinear optical effects in Hg1−xCdxTe1

The alloy semiconductor Hg_1−xCd_xTe has widespread use in modern infrared detection equipment. By adjusting the ratio of Hg to Cd, the energy gap can be tailored to any desired value between 0 eV (x = 0.17) to 1.4 eV (x = 1.0). For values of x near 0.2 the electron effective mass is small, giving rise to a large spin-level splitting factor, or ɡ-value. We have examined two nonlinear optical effects which depend upon the high ɡ-value found in small gap Hg_1−xCd_xTe. These are the spin-flip Raman laser and 4-photon mixing. In each case we employ CO₂ lasers as the input source. In order to achieve resonant enhancement, we adjust the energy gap so that the absorption edge at the temperature of operation, 4 K, is near 10 μm; the required composition is Hg_0.77Cd_0.23Te.During operation as a spin-flip Raman laser, we observe 1st Stokes, 2nd Stokes and anti-Stokes signals, with a basic tunability of 3.8 cm⁻¹/kG for the 1st Stokes radiation. In the 4-photon mixing mode, we see resonant production of an output signal at frequency ω₄ = 2ω₂ − ω₁, where ω₂ and ω₁ are the frequencies of the two CO₂ pump lasers. We also observe under some conditions 6 photon mixing, i.e. ω₆ = 3ω₂ − 2ω₁.     

Fundamental studies and device application of δ-doping in GaAs Layers and in AlxGa1−xAs/GaAs heterostructures

In addition to the realization of atomically abrupt interfaces in III–V semiconductors by molecular beam epitaxy, the confinement of donor and acceptor impurities to an atomic plane normal to the crystal growth direction, called-doping, is important for the fabrication of artifically layered semiconductor structures. The implementation of-function-like doping profiles by using Si donors and Be acceptors generates V-shaped potential wells in GaAs and Al_xGa_1–xAs with a quasi-two-dimensional (2D) electron (or hole) gas. In this review we define three areas of fundamental and device aspects associated with-doping. (i) The prototype structure of-doping formed by a single atomic plane of Si donors in GaAs allows to study the 2D electron gas by magnetotransport and tunneling experiments, to study the metal-insulator transition, and to study central-cell and multivalley effects. In addition, non-alloyed ohmic contacts to GaAs and GaAs field-effect transistors (-FETs) with a buried 2D channel of high carrier density can be fabricated from-doped material. (ii) GaAs sawtooth doping superlattices, consisting of a periodic sequence of alternating n- and p-type-doping layers equally spaced by undoped regions, emit light of high intensity at wavelengths of 0.9 < <1.2 [m], which is attractive for application in photonic devices. The observed carrier transport normal to the layers due to tunneling indicates the feasibility of this superlattice as effective-mass filter. (iii) The confinement of donors (or acceptors) to an atomic (001) plane in selectively doped Al_xGa_1–xAs/GaAs heterostructures leads to very high mobilities, to high 2D carrier densities, and to a reduction of the undesired persistent photo-conductivity. These-doped heterostructures are thus important for application in transistors with improved current driving capabilities.Extended version of a paper presented at the18th Int. Symp. GaAs Related Compounds (Heraklion, Crete, 1987)     

57Fe Mössbauer and infrared studies of the system Co1−x Cd x Fe2O4

Mössbauer and infrared studies were made on samples of the ferrite system Co_1–xCd_xFe₂O₄ x=0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1. Mössbauer spectra were taken at room temperature. The spectra of the samples withx0.7 showed well defined Zeeman patterns and they have been analyzed with two components, one due to A-site Fe³⁺ ions, and the other due to B-site Fe³⁺ and Fe²⁺ ions. The pattern due to B-site appeared to be composite and an explanation is given. The spectra withx=0.9 and 1 showed only a quadrupole splitting. The effect of cadmium substitution on the various hyperfine interactions has been discussed and the cationic distribution has been deduced for all values ofx. Far infrared spectra of the ferrite samples in the range 200–700 cm^–1 were reported. Four bands were observed: the high frequency bandv ₁ is assigned to tetrahedral complexes, and the low frequency bandv ₂ to octahedral complexes, a small bandv ₃ is due to Co²⁺-O^2– complexes andv ₄ is assigned to the lattice vibration of the system. The splitting occurred in thev ₁ andv ₂ bands atx=0.9 and inv ₂ atx=1, indicating the presence of Fe²⁺ ions in octahedral sites.