Electrical and Thermal Transport Properties of Ge1–xPbxCuySbyTeSe2y

Balancing the contradictory relationship between thermoelectric parameters, such as effective mass and carrier mobility, is a challenge to optimize thermoelectric performance. Herein, the exceptional thermoelectric performance is realized in GeTe through collaboratively optimizing the carrier and phonon transport via stepwise alloying Pb and CuSbSe₂. The formation energy of Ge vacancy is efficiently bolstered by alloying Pb, which reduces carrier density and carrier scattering to maintain superior carrier mobility in GeTe. Additionally, CuSbSe₂, acting as an n-type dopant, further modulates carrier density and validly equilibrates carrier mobility and effective mass. Accordingly, the promising power factor of 45 µW cm⁻¹ K⁻² is achieved at 723 K. Meanwhile, point defects are found to significantly suppress phonons transport to descend lattice thermal conductivity by Pb and CuSbSe₂ alloying, which barely impacts the carrier mobility. A combination with superior carrier mobility and lower lattice thermal conductivity, a maximum ZT of 2.2 is attained in Ge_0.925Pb_0.075Cu_0.005Sb_0.005TeSe_0.01, which corresponds to a 100% promotion compared with that of intrinsic GeTe. This study provides a new indicator for optimizing carrier and phonon transport properties by balancing interrelated thermoelectric parameters.     

On the preparation and photoelectric properties of Tl1–x In1–x Sn x Se2 (x = 0.1–0.25) alloys

The technological conditions for growing single crystals of Tl_1–x In_1–x Sn _x Se₂ (x = 0.1–0.25) alloys are developed. The spectral distribution of the photoconductivity of the grown crystals at T = 300 K and thermally stimulated conductivity are studied. The effect of In³⁺cation substitution with Sn⁴⁺ in Tl_1–x In_1–x Sn _x Se₂ (x = 0.1–0.25) alloys on their photoelectric properties is shown.     

Properties of epitaxial (Al x Ga1 − x As)1 − y C y alloys grown by MOCVD autoepitaxy

The growth of epitaxial Al _x Ga_{1 ? x} As:C alloys by metal-organic chemical vapor deposition (MOCVD) at low temperatures results in the formation of quaternary (Al _x Ga_{1 ? x} As)_{1 ? y} C _y alloys, in which carbon atoms can be concentrated at lattice defects in the epitaxial alloy with the formation of impurity nanoclusters.     

Synthesis of compositionally different multicomponent metal-oxide films (SnO2) x (ZnO)1 − x (x = 1–0.5)

The study is concerned with high-purity SnO₂ and ZnO powders produced from salt solutions of corresponding metals by low-temperature hydrothermal synthesis. Fragments of SnO₂ and ZnO ceramic targets formed as 1 × 8 cm bars are fabricated by dry pressing. The bars are used to form composite targets for ion-beam sputtering and the fabrication of compositionally different (SnO₂) _x (ZnO)_{1 ? x} (x = 1–0.5) films appropriate for the production of gas sensors or transparent electronic devices. The optical and electrical parameters of the films with different compositions are studied.     

Spectral shift of photoluminescence bands of the (SiC)1−x (AlN)x epitaxial films due to laser annealing

The effect of laser annealing on the photoluminescence properties of (SiC)_1?x (AlN)_x epitaxial films was studied. It was proposed that annealing causes the displacement of the Al and N atoms from their lattice sites and the formation of Al_Si-N_C donor-acceptor pairs acting as the luminescence centers. According to this model, the increase in the annealing time is accompanied by the formation of donor-acceptor pairs with the shortest interatomic distances at the expense of associations of the distant defects and by a shift of the respective photoluminescence band to the high-energy spectral region.     

Relaxation Dynamics and Threading Dislocations in ZnSe and ZnS y Se1−y /GaAs (001) Heterostructures

The design of lattice-mismatched semiconductor devices requires a predictive model for strains and threading dislocation densities. Previous work enabled modeling of uniform layers but not the threading dislocations in device structures with arbitrary compositional grading. In this work we present a kinetic model for lattice relaxation which includes misfit–threading dislocation interactions, which have not been considered in previous annihilation–coalescence models. Inclusion of these dislocation interactions makes the kinetic model applicable to compositionally graded structures, and we have applied it to ZnSe/GaAs (001) and ZnS _y Se_1?y /GaAs (001) heterostructures. The results of the kinetic model are consistent with the observed threading dislocation behavior in ZnSe/GaAs (001) uniform layers, and for graded ZnS _y Se_1?y /GaAs (001) heterostructures the kinetic model predicts that the threading dislocation density may be reduced by the inclusion of grading buffer layers employing compositional overshoot. This “dislocation compensation” effect is consistent with our high-resolution x-ray diffraction experimental results for graded ZnS _y Se_1?y /GaAs (001) structures grown by photoassisted metalorganic vapor-phase epitaxy.     

First-principles investigation of the optical properties of CuIn(SxSe1–x)2

We optimized the lattice structure of sulfur-doped CuInSe₂ using first principles. The lattice constants for CuIn(S_xSe_1–x)₂ vary linearly with x according to a(x)=–0.02828x+0.58786 nm and c(x)=–0.05692x+1.1834 nm, which agree well with experimental data. The optical properties of CuIn(S_xSe_1–x)₂ were then systematically investigated using first-principles calculations with the HSE06 functional. We present data for the complex dielectric function, refractive index, extinction coefficient, reflectivity index, absorption coefficient, and optical bandgap for CuIn(S_xSe_1–x)₂. The optical bandgap E_g obtained from the absorption coefficient is 1.07 eV for CuInSe₂ and 1.384 eV for CuInS₂. These values are very close to experimental results, indicating that first-principles calculations can yield accurate bandgap values. The optical bandgap of CuIn(S_xSe_1–x)₂ increases linearly with the sulfur concentration according to E_g=0.3139x+1.0825 eV.     

Photosensitivity of thin-film structures based on (CuInSe2)x(2ZnSe)1−x solid solutions

Polycrystalline (CuInSe₂)_x(2ZnSe)_1−x films (x=0.6–1.0) with p-type conductivity and a thickness of 0.5–0.9 μm were obtained by pulsed laser evaporation. It is shown that a chalcopyrite-sphalerite transition occurs in the above system for x=0.7. The obtained films were used to fabricate the photosensitive structure of the In/p-(CuInSe₂)_x(2ZnSe)_1−x and InSe(GaSe)/(CuInSe₂)_x(2ZnSe)_1−x types. Spectral dependences of photovoltaic-conversion quantum efficiency were studied, and the photosensitivity of the structures in relation to the type of energy barrier and the composition was analyzed. It is concluded that the structures under consideration can be used as broadband photovoltaic converters. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 34, No. 5, 2000, pp. 576–581. Original Russian Text Copyright ? 2000 by V. Rud’, Yu. Rud’, Bekimbetov, Gremenok, Bodnar’, Rusak.     

Study of the composition, structure, and optical properties of a-Si1 − x C x :H〈Er〉 films erbium doped from the Er(pd)3 complex compound

Rutherford backscattering, IR spectroscopy, ellipsometry, and atomic-force microscopy are used to perform an integrated study of the composition, structure and optical properties of a-Si_{1 ? x} C _x :H〈Er〉 amorphous films. The technique employed to obtain the a-Si_{1 ? x} C _x :H〈Er〉 amorphous films includes the high-frequency decomposition of a mixture of gases, (SiH₄) _a + (CH₄) _b , and the simultaneous thermal evaporation of a complex compound, Er(pd)₃. It is demonstrated that raising the amount of CH₄ in the gas mixture results in an increase in the carbon content of the films under study and an increase in the optical gap E _g ^opt from 1.75 to 2.2 eV. Changes in the composition of a-Si_{1 ? x} C _x :H〈Er〉 amorphous films, accompanied, in turn, by changes in the optical constants, are observed in the IR spectra. The ellipsometric spectra obtained are analyzed in terms of multiple-parameter models. The conclusion is made on the basis of this analysis that the experimental and calculated spectra coincide well when variation in the composition of the amorphous films with that of the gas mixture is taken into account. The existence of a thin (6–8 nm) silicon-oxide layer on the surface of the films under study and the validity of using the double-layer model in ellipsometric calculations is confirmed by the results of structural analyses by atomic-force microscopy.     

Comparison of III–V Heterostructures Grown on Ge/Si,Ge/SOI,and GaAs

Semiconductors - III–V/Ge/Si(001), III–V/Ge/SOI(001), and III–V/GaAs(001) heterostructures are fabricated and investigated. The Ge buffer layer for the III–V/Ge/Si structure...     

Electrochemical Deposition and Characterization of Thermoelectric Ternary (Bi x Sb1?x )2Te3 and Bi2(Te1?y Se y )3 Thin Films

Thermoelectric thin films of the ternary compounds (Bi _x Sb_1?x )₂Te₃ and Bi₂(Te_1?y Se _y )₃ were synthesized using potentiostatic electrochemical deposition on gold-coated silicon substrates from aqueous acidic solutions at room temperature. The surface morphology, elemental composition, and crystal structure of the deposited films were studied and correlated with preparation conditions. The thermoelectric properties of (Bi _x Sb_1?x )₂Te₃ and Bi₂(Te_1?y Se _y )₃ films, i.e., Seebeck coefficient and electrical resistivity, were measured after transferring the films to a nonconductive epoxy support. (Bi _x Sb_1?x )₂Te₃ thin films showed p-type semiconductivity, and the highest power factor was obtained for film deposited at a relatively large negative potential with composition close to Bi_0.5Sb_1.5Te₃. In addition, Bi₂(Te_1?y Se _y )₃ thin films showed n-type semiconductivity, and the highest power factor was obtained for film deposited at a relatively small negative potential, having composition close to Bi₂Te_2.7Se_0.3. In contrast to Bi₂Te_2.7Se_0.3 thin films, an annealing treatment was required for Bi_0.5Sb_1.5Te₃ thin films to achieve the same magnitude of power factor as Bi₂Te_2.7Se_0.3. Therefore, Bi₂Te_2.7Se_0.3 thin films appear to be good candidates for multilayer preparation using electrochemical deposition, but the morphology of the films must be further improved.     

Structural and spectral features of MOCVD Al x Ga y In1 ? x ? y As z P1 ? z /GaAs (100) alloys

The study is concerned with MOCVD epitaxial heterostructures grown on the basis of Al _x Ga _y In_{1 ? x ? y} As _z P_{1 ? z} quinary alloys in the region of alloy compositions isoperiodic to GaAs. By the X-ray diffraction technique and atomic force microscopy, it is shown that, on the surface of the heterostructures, there are nanometric objects capable of lining up along a certain direction. From calculations of the crystal lattice parameters with consideration for internal strains, it can be inferred that the new compound is a phase based on the Al _x Ga _y In_{1 ? x ? y} As _z P_{1 ? z} alloy.     

Structural and electronic properties of Si1 − x Ge x binary semiconducting alloys under the effect of temperature and pressure

Based on the empirical pseudo-potential method which incorporates compositional disorder as an effective potential, the band structure of Si_{1 ? x} Ge _x alloy are calculated for different alloy composition x. The effect of temperature and pressure on the electronic band structure of the considered alloy has been studied. Monotonic decreasing and increasing functions are obtained for the temperature and pressure dependent form factors respectively. Some physical quantities as band gaps, bowing parameters, and the refractive index of the considered alloy with different Ge concentration and under the effect of temperature and pressure are calculated. The results obtained are found in good agreement with the experimental and published data.     

Structure and optical properties of heterostructures based on MOCVD (Al x Ga1 − x As1 − y P y )1 − z Si z alloys

Epitaxial heterostructures produced by MOCVD on the basis of Al _x Ga_{1 ? x} As ternary alloys with the composition parameter x ≈ 0.20–0.50 and doped to a high Si and P atomic content are studied. Using the high-resolution X-ray diffraction technique, scanning electron microscopy, X-ray microanalysis, Raman spectroscopy, and photoluminescence spectroscopy, it is shown that the epitaxial films grown by MOCVD are formed of five-component (Al _x Ga_{1 ? x} As_{1 ? y} P _y )_{1 ? z} Si _z alloys.     

Technology and electronic properties of PHEMT AlGaAs/In y(z)Ga1 − y(z)As/GaAs compositionally graded quantum wells

Graded In _y Ga_{1 ? y} As quantum well epitaxial technology is developed for engineering the band potential profile. The crystal structure of the samples is clarified by high-resolution X-ray diffraction. The influence of quantum-well bending on the crystal and electron transport properties is studied on one- and two-side δ-doped Al_0.23Ga_0.77As/In _y Ga_{1 ? y} As/Al_0.23Ga_0.77As PHEMT heterostructures. The highest InAs content gradient reached is 1.2%/nm for the mean InAs content y = 0. 2. Optimization of the InAs content grading leads to an increase in the electron mobility and concentration. This effect is related to the straightening and deepening of the quantum-well potential profile. In addition, the electron wavefunction shifts toward the quantum-well center, thus reducing electron scattering.     

Effect of Fe doping on structural and magnetic properties of La2/3Ca1/3Mn1−yFeyO3 (y=0–0.03) thin films

We have characterized the magnetic and structural properties of pure and ⁵⁷Fe-doped La_2/3Ca_1/3MnO₃ thin films and targets, substituted with 1% and 3% of ⁵⁷Fe on the Mn site. The films were prepared via high O₂-pressure (500 mTorr) by DC magnetron sputtering on (1 0 0) SrTiO₃ and (1 0 0) LaAlO₃ single-crystal substrates. Mössbauer spectra measured at room temperature confirm the presence of Fe³⁺ with octahedral coordination, thus indicating that Fe is incorporated into the structure by substituting Mn. Structural analysis by X-ray diffraction (XRD) shows that the films are single phase and c-axis oriented and that the Fe doping gives rise to a relaxation of the epitaxial strain. Interestingly, the Curie temperature and the magnetoresistance (MR) show a non-monotonic behavior with Fe doping. This indicates that initially the strain relaxation induced by the Fe doping is more important than the reduction of ferromagnetic coupling due to the Fe incorporation.     

Phase formation under the effect of spinodal decomposition in epitaxial alloys of Ga x In1 − x P/GaAs(100) heterostructures

The effect of instability of alloys of Ga _x In_{1 − x} P/GaAs(100) semiconductor epitaxial heterostructures in the composition region x ≈ 0.50 is studied by X-ray diffraction and electron microscopy. The possibility of emergence of modulated relaxation structures on the surface of a Ga _x In_{1 − x} P alloy is shown. This phenomenon is accompanied by the emergence of satellites of main X-ray reflections corresponding to a single-phase structure.     

On the resonant level of chromium in the rhombohedral and cubic phases of Pb1 − x − y Ge x Cr y Te alloys

The temperature dependences of the Hall coefficient (4.2 K ≤ T ≤ 300 K, B ≤ 0.07 T) in Pb_{1 ? x ? y} Ge _x Cr _y Te alloys (x = 0.03–0.08, y ≤ 0.01) are studied. An increase in the absolute value of the Hall coefficient with an increase in temperature is found. This fact is indicative of a decrease in the concentration of free electrons as a result of the motion of the resonant level of chromium stabilizing the Fermi level relative to the conduction-band bottom. The temperature dependences of the Hall coefficient, in satisfactory agreement with the experimental ones, are calculated in the context of the two-band Kane dispersion law allowing for the structural phase transition upon increasing temperature. The energy position and temperature coefficients of the motion of the resonant level of chromium relative to the middle of the band gap in the rhombohedral and cubic phases are determined.