Semiconductor Solid Solutions Research Articles

Effect of composition fluctuations on radiative recombination in narrow-gap semiconductor solid solutions

The photoluminescence of the epitaxial structures based on the narrow-gap CdHgTe solid solutions has been experimentally investigated and the presence of large-scale composition fluctuations localizing carriers in the structures has been established. A model has been proposed for describing the effect of the fluctuations on the radiative recombination rate, the shape of the luminescence spectra, and their peak position. The model describes carrier transport and recombination at the strongly inhomogeneous composition of the solid solution and demonstrates the manifestation of carrier localization in the luminescence spectra.

Mechanism for strong magnetoelectric coupling in dilute magnetic ferroelectrics

The manipulation of atomic-scale magnetization is important from both a fundamental and a practical perspective. Using first-principles density-functional-theory calculations within the hybrid functional approach, we systematically study spin-lattice coupling effects for isolated $3{d}^{4}--3{d}^{7}$ transition-metal dopants in a nonmagnetic, ferroelectric ${\mathrm{PbTiO}}_{3}$ host material. When present at the B-site, a low-spin (or intermediate-spin) to high-spin crossover induces marked ferroelectric-like distortions in the local geometry, characterized by a shift of the dopant ion with respect to the surrounding ${\mathrm{O}}_{6}$ octahedral cage. The origins of this microscopic multiferroic effect are discussed in terms of the pseudo-Jahn-Teller theory for ferroelectricity. The possibility to exploit this phenomenon to achieve strong magnetoelectric coupling, including controlled spin switching, is also investigated. These results provide a further understanding of ferroelectricity and multiferroicity in perovskite oxides, and they suggest a possible pathway to manipulate single atomic spins in semiconductor solid solutions.

Production technology and optical absorption characteristics of CuIn0.95Ga0.05Se2 semiconductor solid solution films

A production technology of thin CuIn0.95Ga0.05Se2 films has been developed based on the method of two-stage selenization of CuIn0.95Ga0.05 precursor by a reactive component (selenium) in a carrier gas (nitrogen) flow. The morphology and structure of obtained films were studied by electron microscopy and X-ray diffraction techniques. The spectral dependence of the optical absorption coefficient was measured.

Investigation of Crystal and Electronic Structures Features of Hf1-xTmxNiSn Semiconductor Solid Solution

The features of structural, energy state and electrokinetic characteristics were investigated for Hf1‑xTmxNiSn solid solution in the range: T = 80 - 400 K, x = 0 - 0.40. It was confirmed partly disorder crystal structure of HfNiSn compound as a result of occupation in the 4a crystallographic site of Hf (5d26s2) atoms by Ni (3d84s2) ones up to ~ 1 % that generates in the crystal structural defects of donor nature. It was shown that introduction of Tm atoms ordered crystal structure (“healing” of structural defects). It was established mechanisms of simultaneous generation of structural defects as acceptors by substitution of Hf (5d26s2) by Tm (4f135d06s2) atoms, and the donor nature defects as a result of the appearance of vacancies in the Sn (4b) atoms sites, which determines the mechanisms of conductivity for Hf1-xTmxNiSn.

Lattice parameters and electronic structure of BeMgZnO quaternary solid solutions: Experiment and theory

BexMgyZn1−x−yO semiconductor solid solutions are attractive for UV optoelectronics and electronic devices owing to their wide bandgap and capability of lattice-matching to ZnO. In this work, a combined experimental and theoretical study of lattice parameters, bandgaps, and underlying electronic properties, such as changes in band edge wavefunctions in BexMgyZn1−x−yO thin films, is carried out. Theoretical ab initio calculations predicting structural and electronic properties for the whole compositional range of materials are compared with experimental measurements from samples grown by plasma assisted molecular beam epitaxy on (0001) sapphire substrates. The measured a and c lattice parameters for the quaternary alloys BexMgyZn1−x with x = 0−0.19 and y = 0–0.52 are within 1%–2% of those calculated using generalized gradient approximation to the density functional theory. Additionally, composition independent ternary BeZnO and MgZnO bowing parameters were determined for a and c lattice parameters and the bandgap. The electronic properties were calculated using exchange tuned Heyd-Scuseria-Ernzerhof hybrid functional. The measured optical bandgaps of the quaternary alloys are in good agreement with those predicted by the theory. Strong localization of band edge wavefunctions near oxygen atoms for BeMgZnO alloy in comparison to the bulk ZnO is consistent with large Be-related bandgap bowing of BeZnO and BeMgZnO (6.94 eV). The results in aggregate show that precise control over lattice parameters by tuning the quaternary composition would allow strain control in BexMgyZn1−x−yO/ZnO heterostructures with possibility to achieve both compressive and tensile strain, where the latter supports formation of two-dimensional electron gas at the interface.

Role of electron‐phonon interaction in the temperature dependence of the phonon mode frequency in II‐VI compound alloys

AbstractWe present an experimental investigation of the temperature dependence of the TO‐phonon mode frequencies for the HgTe‐based II‐VI semiconductor solid solutions. In the case of the ternary Hg0.9Zn0.1Te solid solution was shown a discontinuity in the temperature dependence of the HgTe‐like TO‐mode and of the ZnTe‐like TO‐mode, similar to the Hg0.885Cd0.115Te system [Sheregii et al., Phys. Rev. Lett. 102, 045504 (2009)]. A generalization of the theoretical temperature shift of the phonon mode frequency as analytic equation is derived that includes both the anharmonic contribution and the electron‐phonon e‐p interaction which in this case is returnable the electron subsystem effect on the phonon one. Data show that our equation satisfactorily describes the temperature shift of both Hg0.885Cd0.115Te and Hg0.9Zn0.1Te containing Dirac point (Eg = Γ6–ΓΓ8 = 0) although one of the two constants describing the anharmonic shift of the HgTe‐like mode should be positive what is abnormal too. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Calculation of the Schottky barrier height at the contact between a metal and (SiC)1–x (AlN) x semiconductor solid solution

A simple model of the metal–semiconductor contact that is nonlinear in the concentration of defects when the Schottky barrier is formed by the surface defect states Ei localized at the interface has been proposed. It has been shown that taking into account the nonlinear dependence of the Fermi energy EF on the concentration of defects results in an increase in the Schottky barrier height by 15 to 25%. The calculated values of the Schottky barrier height have been used for the analysis of the current-voltage characteristics of M/(SiC)1–x(AlN)x structures. The theoretical results have been compared with the experimental data.

Thermoelectric properties of thin-film Sb0.9Bi1.1Te2.9Se0.1–C composites

Thin-film nanocomposites of a Sb0.9Bi1.1Te2.9Se0.1 semiconductor solid solution in the carbon matrix have been synthesized. The low-temperature dependences of the electrical resistivity and thermoelectric power have been investigated in the temperature range of 77–300 K. It has been shown that there is a successive change in the dominant mechanisms of electrical conduction: variable-range hopping conduction over localized states lying in a narrow energy band near the Fermi level, hopping conduction over the nearest neighbors, and hopping electron transfer associated with charge carriers excited into localized states near the band edges.

Evolution of the level anticrossing signal in magnetoluminescence of localized excitons in the GaSe–GaTe solid solution

The time dependence of the Zeeman-sublevel anticrossing signal in triplet localized exciton emission in the GaSe0.87Te0.13 semiconductor solid solution has been studied by the time-resolved spectroscopy method under conditions of unpolarized pumping. It has been shown that the anticrossing signal shape changes significantly for the lifetime t of localized excitons. At the time point t = 0, the anticrossing signal is not detected; as t increases, a maximum is formed in the dependence of the exciton emission intensity on the magnetic field (at this stage, the anticrossing signal shape is identical to that observed under conditions of steady-state excitation), which is split into a doublet as t further increases. A theoretical interpretation of the observed time dependence of the Zeeman-sublevel anticrossing signal in localized exciton emission has been proposed. The fine structure parameters and lifetimes of the triplet localized excitons have been determined in different spin states by comparing theory and experiment.

Laser-Induced Modification of Properties of CdZnTe Crystals

The photoconductivity (PC) spectra of CdZnTe (CZT) semiconductor solid solutions obtained from different manufacturers were investigated before and after irradiation with nanosecond laser pulses. Depending of energy density, irradiation of CZT crystals resulted in an increase in the photosensitivity, high-energy shift of the PC spectrum maximum and transformation of its profile. Laser processing with the certain energy densities improved homogeneity in the crystal surface area and provided equalization of structural characteristics in the surface region and bulk of the samples. Irradiation of CZT crystals pre-coated with an In electrode film caused rectification in the I-V characteristics because of the formation of a barrier structure. The application of the obtained In/CZT/Au diodes with low leakage current as X/γ-ray detectors is considered.

Investigation of V1-xTixFeSb Semiconductor Solid Solution. II. Peculiarities of Crystal and Electronic Structure

The peculiarities of the crystalandelectronicstructureof V1-xTixFeSb, х = 0 – 0,20, semiconductor solid solution wereinvestigated. Themechanismofgenerationofstructuraldefectsofacceptoranddonornatureisdescribed. In particular the nature of donors in n-VFeSb was established (“a priori doping”) as a result of presence of vacancies in Sb atomic site (4b). The obtained result lays in the basis of the technology for obtaining thermoelectric materials based on n-VFeSb with maximal efficiency of thermal to electrical energy conversion.

Investigation of V1-xTixFeSb Semiconductor Solid Solution. I. Peculiarities of Electrokinetic Characteristics

The peculiarities of the temperature and concentration characteristics of resistivity and thermopower of V1-xTixFeSb semiconductor solid solution were investigated in the temperature and concentration ranges of T = 4.2 -400 K and Ті ≈ 9.5·1019–3.6·1021 см-3 (х = 0.005 - 0.20), respectively. The existence of previously unknown mechanism for the generation of structural defects with donor nature which determined the conduction of n-VFeSb and V1-xTixFeSb was established. The acceptor type of structural defects generated in V1-xTixFeSb by substitution of V atoms by Ti ones was confirmed.

First-Principles Investigation of Optoelectronic and Redox Properties of (Ta1–xNbx)ON Compounds for Photocatalysis

We investigate essential fundamental properties of monoclinic (Ta1–xNbx)ON (x = 0.0625, 0.125, 0.25, and 0.5) solid solution semiconductor materials for water splitting using first-principles computations on the basis of density functional theory (DFT) and density functional perturbation theory (DFPT) using the PBE and HSE06 functionals. The formation energies, band gaps, UV–vis optical absorption coefficients, dielectric constants, charge carrier effective masses, and band edge energy positions of these compounds are evaluated. Similarly to TaON, our calculations reveal strongly 3D delocalized characters of the band edge electronic states through the crystal lattices, high dielectric constants, small hole effective masses along the [001] direction, and small electron effective masses along the [100] direction. This leads to good exciton dissociation ability into free charge carriers, good hole mobility along the [001] direction, and good electron mobility along the [100] direction. The main difference, h...

Influence of the electron-phonon interaction on the temperature dependence of the phonon mode frequency in the II-VI compound solid solutions

We present an experimental investigation of the temperature dependence of the TO-phonon mode frequencies for the HgTe-based II-VI semiconductor solid solutions. In the case of the ternary Hg0.9Zn0.1Te solid solution was shown a discontinuity in the temperature dependence of the HgTe-like T0-mode and of the ZnTe-like T1-mode, similar to the Hg0.85Cd0.15Te system [Sheregii et al., Phys. Rev. Lett. 102, 045504 (2009)]. A generalization of the theoretical temperature shift of the phonon mode frequency as analytic equation is derived that includes both the anharmonic contribution and the electron-phonon e-p interaction which in this case is returnable—the electron subsystem effect on the phonon one. Data show that our equation satisfactorily describes the temperature shift of both Hg0.85Cd0.15Te and Hg0.90Zn0.10Te containing Dirac point (Eg ≡ Γ6 – Γ8 = 0) although one of the two constants describing the anharmonic shift of the HgTe-like mode should be positive what is abnormal too. In the case of the Hg0.80Cd0.20Te and Hg0.763Zn0.237Te solid solution, the role of the returnable e-p contribution is negligible but a positive temperature shift for the HgTe-like modes occurs. This result does not allow to explain the positive temperature shift of these modes merely by the contribution of the (e-p) interaction. Indeed, the relativistic contribution to the chemical bonds induces an abnormal temperature shift of the electron states in Hg-based semiconductors—the effect is expected since the Hg d spin-orbit split contribution to chemical bonds may lead to an abnormal temperature shift of the HgTe-like modes.

Unfolding the band structure of disordered solids: From bound states to high-mobility Kane fermions

Supercells are often used in ab initio calculations to model compound alloys, surfaces and defects. One of the main challenges of supercell electronic structure calculations is to recover the Bloch character of electronic eigenstates perturbed by disorder. Here we apply the spectral weight approach to unfolding the electronic structure of group III-V and II-VI semiconductor solid solutions. The illustrative examples include: formation of donor-like states in dilute Ga(PN) and associated enhancement of its optical activity, direct observation of the valence band anticrossing in dilute GaAs:Bi, and a topological band crossover in ternary (HgCd)Te alloy accompanied by emergence of high-mobility Kane fermions. The analysis facilitates interpretation of optical and transport characteristics of alloys that are otherwise ambiguous in traditional first-principles supercell calculations.

Hybrid technique for growing homogeneous single crystals of semiconductor solid solutions from melt

A concept and fundamentals of a hybrid technique for growing homogeneous single crystals of semiconductor solid solutions (SSs) from melt are presented. The growth consists of two stages. In the first stage, a single crystal with a specified concentration of the more refractory component is grown by an innovative method of directional constitutional supercooling of a melt in the steady-state mode. In the second stage, the melt is fed with the second component. Using an example of the classical Ge-Si system, the concentration profiles of the components along the crystal axis are calculated and the SS growth dynamics ensuring single crystallinity over the entire ingot length is determined. An analysis of the results yields the optimal technological parameters and conditions for growing homogeneous single crystals of SSs of a specified composition and size.

Concentration anomalies of the thermal conductivity in PbTe-PbSe semiconductor solid solutions

Studies of the concentration (0–3 mol% PbSe) and temperature (250–670 K) dependences of the lattice thermal conductivity λp in PbTe–PbSe semiconductor solid solutions have shown that in the range of 0.75–1.25 mol% PbSe an anomalous increase in λp under increasing PbSe concentration takes place in the λp isotherms, plotted as λp/λp0, where λp0 is the lattice thermal conductivity in the absence of PbSe. The observed effect is attributed to critical phenomena and self-organization processes accompanying the transition from dilute solid solutions to an impurity continuum.

The stochastic model for ternary and quaternary alloys: Application of the Bernoulli relation to the phonon spectra of mixed crystals

To understand and interpret the experimental data on the phonon spectra of the solid solutions, it is necessary to describe mathematically the non-regular distribution of atoms in their lattices. It appears that such description is possible in case of the strongly stochastically homogenous distribution which requires a great number of atoms and very carefully mixed alloys. These conditions are generally fulfilled in case of high quality homogenous semiconductor solid solutions of the III–V and II–VI semiconductor compounds. In this case, we can use the Bernoulli relation describing probability of the occurrence of one n equivalent event which can be applied, to the probability of finding one from n configurations in the solid solution lattice. The results described in this paper for ternary HgCdTe and GaAsP as well as quaternary ZnCdHgTe can provide an affirmative answer to the question: whether stochastic geometry, e.g., the Bernoulli relation, is enough to describe the observed phonon spectra.

Visualization of Electrochemical Reactions by Redox-dependent Quenching of Photoluminescence from ZnS-AgInS2 Solid Solution Semiconductor Nanoparticles

Visualization of Electrochemical Reactions by Redox-dependent Quenching of Photoluminescence from ZnS-AgInS2 Solid Solution Semiconductor Nanoparticles

Band gap-tunable (CuAg)xIn2xZn2(1−2x)S2 solid solutions synthesized by hydrothermal method with ultrasonic assistance and their photocatalytic H2 production performance

Abstract A series of (AgCu) x In 2 x Zn 2(1−2 x ) S 2 solid solutions, which were usually obtained at high temperature, were successfully prepared in an environmental-friendly condition via a simple and cost-effective hydrothermal method with ultrasonic assistance. The physical and photophysical properties of these multicomponent semiconductor solid solutions were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), UV–visible diffuse reflectance spectra (UV–Vis) and N 2 adsorption–desorption techniques. XRD patterns of prepared samples shifted to lower angles as the value of x increased, indicating that (AgCu) x In 2 x Zn 2(1−2 x ) S 2 solid solutions had been formed. UV–Vis spectra of the solid solutions shifted monotonically to long wavelength side as M/Zn (M = Cu and Ag) increased, demonstrating that the band gap of the solid solution photocatalysts could be precisely controlled with the variation of the composition. SEM and TEM images showed that the solid solutions were microspheres in morphology. The microspheric morphology, as well as a proper band structure of the solid solutions, influenced its photocatalytic activity. The photocatalytic H 2 evolution from an aqueous solution containing Na 2 S and Na 2 SO 3 under visible-light irradiation over (AgCu) x In 2 x Zn 2(1−2 x ) S 2 solid solutions were evaluated. The Ru (1.5 wt%)-loaded (AgCu) 0.1 In 02 Zn 1.6 S 2 had the highest photocatalytic activity for H 2 evolution.