Appearance of flaws in layers of AlxGa1−xSb solid solutions during epitaxial growth from the liquid phase

Layers of Al_xGa_1–xSb (x0.7) solid solutions were grown epitaxially from the liquid phase on substrates of gallium antimonide. Aluminum was added to the melt during the buildup of an epitaxial layer. In these layers were found inclusions of the solvent as well as regions of localized chemical inhomogeneities. It is shown here that the appearance of such flaws is intimately related to the relief which the GaSb substrate has formed by the time aluminum enters into the solution. A mechanism of this flaw formation is suggested.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 75–80, June, 1976.     

Surface-barrier structures on AlxGa1−xSb. II. Band gap dependence of barrier height

The short-circuit photocurrent is used to find the forbidden gap width E_g and barrier height _B of Pd-n-Al_xGa_1–xSb (0.1 s x 0.7) surface-barrier structure fabricated electrochemically. The barrier height was also determined from the capacitive voltage cutoff and the current-voltage characteristics. For metal-n-Al_xGa_1–xSb contacts the linear approximation to _B(E_g) is given by _B = 0.64E_g + 0.16 eV. In some samples the photoresponse spectrum has a hump, indicating the effects of deep levels.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 26–31, June, 1979.     

Lattice distortion in the solid solutions of UAsxSe1−x

The solid solutions of UAs_xSe_1−x for x = 0.10−0.40 were studied by X-ray diffraction at the temperature region 130–200 K. A rhomboedrical distortion of the crystal structure below T_c was observed. A dependence of an intersitial angle and coefficient of spontaneous magnetostriction on the temperature or the composition of samples was determined.     

Analysis of critical melt supercooling for heteroepitaxy of AlxGa1−xSb by GaSb

Thermodynamic computations of the critical supercooling of a melt are performed for the case of heteroepitaxy of a solid Al_xGa_1–xSb solution on a GaSb substrate for which there should be no substrate etching. Three kinds of supercoolings are examined, where _cr ⁽¹⁾ is the supercooling for which the change in the system Gibbs energy should equal zero because of dissolution, _cr ⁽¹⁾ is the supercooling for which the diminution in the system Gibbs energy due to substrate dissolution equals the energy being liberated during crystallization of the Al_xGa_1–xSb solid solutions layer. Finally, the influence of the specific free interphasal energy of the substrate-melt interface on the result of computing the critical supercooling (the supercooling _cr ⁽¹⁾ is considered.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 47–52, February, 1988.In conclusion, the authors are grateful to senior scientific worker A. P. Vyatkin and scientific worker L. E. Épiktetova for interest in the research and for useful discussion.     

Defects and localized states in MBE-grown GaAs1−x N x solid solutions prepared by molecular-beam epitaxy

Defects and localized states have been studied for molecular-beam-epitaxy (MBE)-grown high-resistivity and undoped GaAs_1?x N _x films with a N concentration not exceeding approximately 1.0 at.%. The crystalline quality of the films and hence the defects and localized states were determined by high-resolution X-ray diffraction, photoluminescence spectra, capacitance versus voltage measurements and photoinduced current transient spectra of GaAs and GaAs_1?x N _x layers. It was concluded that incorporation of low concentrations of N into MBE-grown GaAs_1?x N _x films promotes the formation of high densities of deep centres similar to EL2 donors, leading to heavy compensation of the films by some unidentified acceptors. GaAs antisite acceptors were believed to be responsible for the said compensation. A prominent defect band near 1.33-1.38 eV also appeared to be associated with these defects. The most prominent centres in dilute GaAs_1?x N _x films with N content less than 0.35 at.% seem to be the EL2 donors and the hole traps located near E _v +0.3 eV.     

Band-to-band recombination in GaxIn1−xSb

The carrier lifetimes in Ga_xIn_1−xSb for radiative and Auger recombination are calculated for the temperature range 77–300 K and the composition range 0 ⩽ x ⩽ 1. The possible band-to-band Auger recombination mechanisms in direct-gap semiconductors are investigated. The Auger rates are calculated, including Boltzmann statistics and nonparabolic bands, using the Kane-band model. In the low temperature range, for lightly doped material, the carrier lifetime is determined by radiative recombination. At higher temperatures the CHCC process is dominant in n-type Ga_xIn_1−xSb but in p-type material the CHLH process is dominant. The influence of CHSH processes on the carrier lifetime is appreciable in p-type GaSb. The calculations are compared with experimental data reported by other authors.     

Optical properties of Li1−xNb1−xEu2xO3 solid solutions

Abstract

The effects of europium substitution on crystalline solubility, structural changes and optical properties of LiNbO₃ is reported. Li_1?xNb_1?xEu_2xO₃ solid solutions exist over a very limited range of europium concentrations (x ≤ 0.01). The solid solutions were characterized by X-ray powder diffraction and density measurements. Within the range of compositions of the solid solutions, the optical properties (emission and excitation spectra) of the Eu³⁺ ions have been characterized. The obtained optical data indicate that two equally abundant europium luminescent species exist in the stoichiometric speciments; these correspond to the Eu³⁺ ions occupying the Li⁺ and Nb⁵⁺ sites, in agreement with the replacement mechanism which is inferred from density measurements. Other Eu³⁺ luminescent species which appear to be closely related with lithium deficiency were found to exist in nonstoichiometric samples, in addition to those which are present in the stoichiometric materials.     

New type of excitonic radiation in the solid solutions CdS1−x Sex

Manifestations of bulk crystalline regions with stacking faults are detected in the reflection and photoluminescence spectra of CdS_1-x Sex crystals with a variety of compositions. The magnitude of the crystal-field anisotropy and the spin-orbit splitting in these crystals are estimated. It is shown that reabsorption affects the form of the photoluminescence in crystals with stacking faults. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 3, 221–225 (10 August 1999)     

Interaction of excitons in indirect solid solutions of In1−xGaxP at high levels of excitation

The cathode luminescence spectra of GaP and solid solutions of In_1–xGa_xP (with an indirect energy band structure) obtained by liquid-phase epitaxy are investigated at T=77 and 9°K. It is established that the recombination of excitons on neutral donors and the pure exciton recombination with the participation of TA (=13±1 meV), LA (=31±1 meV), and TO (=43±2 meV) phonons. dominate in the low-temperature luminescence spectra of GaP and In_1–xGa_xP with a small concentration of photon impurities. The complex luminescence band that arises for sufficiently high levels of excitation and at T = 9°K is attributed to the luminescence of an electron-hole drop (EHD). The transformation of spectral form of the EHD band with the transition from GaP to In_1–xGa_xP is attributed to a simultaneous reduction in the contribution of the TA and TO replicas and to the appearance of a phononless component in the luminescence of the EHD.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 37–40, September, 1985.     

Magnetic properties of solid solutions of the system ErxY1−xFe2

The magnetic properties of the system Er_xY_1–xFe₂ (MgCu₂ structure) in the temperature range 80–800°K are investigated. The magnetization and the coercive force H_c are measured as a function of T. For alloys with x= 0.5–1 there is a magnetic compensation point _c. The composition dependence of _c, the magnetic moment of the alloy and of the iron atoms Fe are determined. An H_c anomaly is observed in _c. In order to explain the results obtained, the presence of two types of magnetically active atoms and three types of exchange interaction are included.Translated from Izvestiya Vysshykh Uchebnykh Zavedenii, Fizika, No. 10, pp. 27–30, October, 1982.     

Photoluminescence of AlxGa1−xAs/GaAs quantum well heterostructures grown by molecular beam epitaxy

Low-temperature photoluminescence measurements on nominally undoped Al_xGa_1–xAs/GaAs quantum well heterostructures (QWHs) grown by molecular beam epitaxy (MBE) exemplified the exclusivelyintrinsic free-exciton nature of the luminescence under moderate excitation conditions. Neither any spectroscopic evidence for alloy clustering in the Al_xGa_1–xAs barriers nor any extrinsic luminescence due to recombination with residual acceptors has been detected in single and double QWHs when grown at 670 °C under optimized MBE growth conditions. Carrier confinement in Al_xGa_1–xAs/GaAs QWHs starts at a well width ofL _z30 nm when x0.25. The minor average well thickness fluctuation ofL _z=4×10^–2nm as determined from the excitonic halfwidth allowed the realization of well widths as low asL _z=1 nm and thus a shift of the free-exciton line as high as 2.01 eV which is close to the conduction band edge of the employed Al_0.43Ga_0.57As confinement layer. The measurements further revealed a strongly enhanced luminescence efficiency of the quantum wells as compared to bulk material which is caused by the modified exciton transition probabilities due to carrier localization.     

Edge emission of AlxGa1−xN

The photoluminesence in the edge emission region of Al_xGa_1−xN> (0 ≦ x ≦ 0.24) has been studied. The compositional dependence of the band gap was studied and the bowing parameter was determined: b = 0.98 eV. With increasing x the edge emission peak broadens, explanation of the mechanism of which has been attempted.     

Cathodoluminescence spectra of Cd1−x Zn x Te solid solutions

An investigation is made of the cathodoluminescence, electrical properties, and structural features of crystals of Cd_1−xZn_xTe solid solutions with composition x ranging from 0.02 to 0.20 mole fraction as compared with CdTe and ZnTe. The main bands of the cathodoluminescence spectra are identified within the range 500–2700 nm. The role of oxygen in Cd_1−xZn_xTe cathodoluminescence is shown. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 67, No. 1, pp. 96–100, January–February, 2000.     

Optimization of optical gain in AlxGa1−xN/GaN/AlxGa1−xN strained quantum well laser

In this paper the optical gain in wurtzite AlGaN/GaN quantum well is studied. The effects of temperature, carrier concentration, quantum well width, and barrier width are analyzed theoretically taken into account the strong built-in electric field effect due to the piezoelectric and spontaneous polarization in the nitride materials. The numerical results clearly show that the increasing of carrier concentration, and decreasing of temperature and well widths, the optical gain increases.     

Crystallographic and optical properties of Li1−xTa1−xEu2xO3 solid solutions

Abstract

The effects of europium substitution on crystalline solubility, structural changes and optical properties of Li_1?xTa_1?xEu_2xO₃ solid solutions are reported. The solid solutions exist over a very limited range of europium concentrations (x ≤ 0.02). They were characterized by X-ray powder diffraction and density measurements. The liquid nitrogen fluorescence and excitation spectra of Eu³⁺ in the solid solutions were measured in the frequency range 12,200–45,450 cm^?1. The emission mainly arises from the ⁵ D ₀ level to Stark components of the five lowest ⁷ F _j (j = 0, 1, 2, 3, 4) states. It was inferred from the analyses of the optical and density data that the Eu³⁺ ions may lie on both Li and Ta sites, but not on the intrinsic vacant lattice sites.     

Structural and optical properties of ZnSe x Te1−-x solid solutions in thin-film form

Solid solutions of ZnSe _x Te_1–x (0. 1 x 1) were synthesized by vacuum fusion of stoichiometric proportions of ZnSe and ZnTe. X-ray diffraction data revealed that they have polycrystalline cubic zinc-blende structure. The calculated unit cell lattice constant (a) for the different compositions in powder form vary linearly, with molecular fractionx following Vegard's law:a(x) = 6.165 – 0.485x. Thin films of ZnSe _x Te_1–x (0.1 x 1) solid solutions deposited onto glass or quartz substrates by thermal evaporation in a vacuum of 10^–4 Pa were found to be polycrystalline with a preferred (1 1 1) orientation. The obtained data were confirmed by electron diffraction. The optical studies showed that ZnSe _x Te_1–x polycrystalline films of different compositions have two direct transitions with corresponding energy gapsE _g andE _g + _so The variations in bothE _g andE _g + _so, withx indicate that ZnSe _x Te_1–x solid solution belongs to an amalgamation-type following quadratic equations with bowing parameters 1.251 and 1.275, respectively.     

Manganese doping of In1−xGaxAsyP1-y films in liquid-phase epitaxy

The manganese doping of In_1–xGa_xAs_yP_1-y(0 y 1) films grown by liquid-phase epitaxy has been investigated. A study has been made of the influence of the solid-solution composition and of the method of introducing the manganese into the solution melt on the electrical properties of the films, and also on the surface morphology, the optical absorption edge, and the mismatch of the film and substrate lattice constants. It is shown that the hole density in the films decreases with decreasing y. The reasons for this are the decrease in the distribution coefficient of the acceptor manganese (from 0.3 to 0.001), the increase in the degree of compensation of the acceptors with donors (from 0.2 to 0.9), and the increase in the acceptor ionization energy. The composition of the InGaAsP:Mn film and the morphology of its surface depend on the method of preparation of the melt, this being explained by the strong interaction of the manganese atoms with the other components of the liquid phase.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 1, pp. 26–34, January, 1992.We thank T. G. Druzhinin, Ya. I. Otman, and V. B. Yabzhanov for helping with the experiments.     

Galvanomagnetic properties of the Al1−x Six nonequilibrium substitutional solid solutions

Galvanomagnetic characteristics of the A_1−x Si_x solid solutions (x<12 at. %) have been studied within a broad range of temperatures (1.8–290 K) and magnetic fields (up to 15 T). An anomaly in the concentration dependence of the Hall coefficient R _H (x,T=290 K) has been revealed near the boundary of absolute instability (x<8.5 at. %) of compounds in the Al_1−x Si_x series. The variation of the Hall coefficient and of the magnetoresistance in the A_1−x Si_x series at low (T<77 K) temperatures is analyzed within models taking into account the anisotropy in conduction-band electron scattering. Fiz. Tverd. Tela (St. Petersburg) 41, 3–10 (January 1999)