Doping of PbTe and Pb1−xSnxTe with gallium and indium

Precipitations in Indium and Gallium-doped PbTe, SnTe and Pb_1−xSn_xTe are investigated. The compositions of the precipitated phases are PbGa₆Te₁₀ SnGa₆Te₁₀ and PbIn₆Te₁₀ for binary compounds. For Pb_1−xSn_xTe the precipitated phase composition corresponds to the continuous solid solutions Pb_1−zSn_zGa₆Te₁₀. Basic properties of the new compounds are determined. Their resistivity being of 5 ÷ 6 orders higher than that for Pb(Sn)Te, the anomalous transfer phenomena, observed in highly Ga(In)-doped samples can be explained on the basis of the barrier model.     

Thermally activated de-excitation of the EL2 metastable state in GaAs

Measurements of absorption in the near infrared have been performed on n-type and undoped semi-insulating GaAs containing EL2 the main native defect in GaAs. The whole band of absorption related to EL2 disappeared after 1 μm light illumination when the crystal was cooled to helium temperatures. Measurements of the thermally activated recovery of EL2 absorption have been made. The rate of the de-excitation is well described by the formula: r = 1.7 · 10¹² · exp (−0.36 eV/kT) + 1.6 · 10⁻⁹ · n · exp (−0.085 eV/kT) s⁻¹ where n [cm⁻³] is the concentration of free electrons.     

Absorption and electrical conductivity of CaMoO4 crystals

The electrical conductivity σ of CaMoO₄ crystals was investigated between room temperature and 850°C. The mobility v_v and the diffusion coefficient D_v of the O⁻ ion vacancies have been derived from σ: v_vT = 3300 exp (−1.52 eV/kT) cm² K/Vs, D_v = (0.1…1) × exp (−1.52 eV/kT) cm²/s. An absorption occuring in crystals which are reduced or X-irradiated at low temperatures is dichroitic and caused by Mo⁵⁺ ions. For measurement in c direction the oscillator strength of the 680 nm absorption band is found to be about 0.1.     

Liquid-Phase Epitaxy of (Hg,Cd)Te on CdTe Substrates by a Vertical Dipping Technique

Hg_1−xCd_xTe layers on CdTe substrates were grown from Te-rich melt solutions by a vertical dipping technique using a special quasi-closed system with ground-glass sealing. Results are good reproducibilities of the electrical properties after annealing in Hg-rich atmosphere (p77 ≈ 2 · 10¹⁶ cm⁻³ μ77 ≈ 500 cm² V⁻¹ s⁻¹) and of the x-value, respectively. A horizontal position of the substrate downwards to the melt solution yields, in difference to a vertical one, to homogeneous layer thicknesses. Short meltback steps before growth leads to sharper profiles of composition.     

Solubility of CaO in CaF2 crystals

By means of conductivity investigations the solubility of CaO in CaF₂ crystals was estimated to be C_L(CaO) ≈︁ 3.7 exp (-0.68 eV/kT) = 3.7 exp (-7900 K/T) and the diffusion constant of O⁻ ions in CaF₂ D(O⁻) ≈︁ 3 exp (-2.2 eV/kT) cm²/s = 3 exp (-25 500 K/T) cm²/s.     

Impurity diffusion of 114In in Cu

Using the tracer-standard sectioning technique the impurity diffusion of indium in copper has been investigated in the temperature range from 798.1 to 1081.0°C. For the frequency factor and the activation energy, respectively, the following values were determined: D₀₂ = 1.87 cm² · s⁻¹; Q₂ = 2.034 eV. The results are compared with predictions of theoretical models of the impurity diffusion in metals.     

Ionic conductivity of BaF2 crystals

By fitting theoretically calculated to experimentally found lg σT ÷ 1/T dependencies (σ conductivity) there were obtained: the free formation enthalpy of anti-Frenkel defects g_AF = 1.81 eV − 7.85 kT, and the mobilities v_V and v_i of F⁻ ion vacancies and interstitials: v_VT = 240 exp (−0.59 eV/kT) cm² K/Vs, v_iT = (4080 + 610) exp (−0.79 eV/kT) cm² K/Vs. The free association enthalpies were reestimated for complexes consisting of single foreign cations (Na⁺, K⁺, Y³⁺, La³⁺, Tm³⁺, Yb³⁺) and the corresponding charge-compensating defects. At the melting point of BaF₂ at least 5.7 per cent of the F⁻ ions are disordered.     

Electrical properties of PbxSn1‐xS thin films prepared by hot wall deposition method

The Pb_xSn_1‐xS (x = 0 – 0.25) thin films were prepared on glass substrates by hot wall vacuum deposition. The films were polycrystalline monophase in nature and had orthorhombic crystal structure. The thickness of the films was about 2‐3 μm. The temperature dependences of the conductivity were measured in the temperature range from 150 to 420 K. The films revealed p‐type of conductivity. The Seebeck coefficient and conductivity values of the films was in the range of α = 6 – 360 μV/K and σ = 4.8×10^‐5 – 1.5×10^‐2 Ω^‐1·cm^‐1, respectively, at room temperature depending on concentration of the lead in the films. The lead atoms created the substitution defects Pb_Sn in the crystal lattice of the Pb_xSn_1‐xS. These defects formed the donor energy levels in the band gap. The activation energy of the films increased in the range ΔE_a = 0.121 – 0.283 eV with increasing of the lead concentration. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Chemical lap polishing of PbTe and Pb1−xSnxTe crystals

Chemical lap polishing of PbTe and Pb_1−xSn_x Te crystals is investigated. A mixture of potassium hexacyanoferrate (III), sodium hydroxide, glycerol and water is used as a polish. The effect of various parameters of the process on the quality of the surface and on the rate of material removal is studied. The quality of the surface is strongly is strongly affected by the composition of the polish. The roughness increases with rising sodium hydroxide concentration but decreases with rising glycerol concentration. If the molar ratio of sodium hydroxide and potassium hexacyanoferrate (III) exceeds the value 0.5 etch figures are formed. The rate of material removal largely depends on the velocity of the relative movement between specimen and cloth, the rate of supply of polishing solution and on the concentration of sodium hydroxide.     

Electric conductivity and lattice disorder of PbMoO4 crystals

From differential thermal analysis (DTA), thermal etching, perfectly reversable redox treatments and electric conductivity it is concluded that the Pb/Mo ratio of the PbMoO₄ crystals is always 1 and that phase transitions do not occur. Pb³⁺ ions detectable by an absorption band at 435 nm cause a p-conductivity due to the reaction Pb³⁺ ⇌ Pb⁺⁺ + e⁺. At elevated temperatures the p-conductivity increases with increasing oxygen partial pressure of the surrounding atmosphere. The influence of foreign ions on the concentration of ionic and electronic defects in PbMoO₄, CaMoO₄, PbO, and PbTiO₃ can be explained by an anti-Frenkel disorder of the oxygen ion sublattice. For PbMoO₄ crystals the mobility O⁻ ion vacancies and the free formation enthalpy of anti-Frenkel defects are found to be v_v = \documentclass{article}\pagestyle{empty}\begin{document}$ \mathop - \limits_T^{9160} $\end{document} exp (−1.15 eV/kT) cm² K/Vs and g_AF = 3.6kT −2.2 eV, respectively.     

Contributions to the surface preparation of semiconductor materials of low hardness

Starting from the general demands made upon semiconductor surfaces (measuring samples, substrates) and the critical material properties, the boundary conditions for the surface preparation of substances of low hardness are stated and technological variants for Bi_1−xSb_x, Pb_1−xSn_xTe, and PbS_1−xSe_x are presented. The results show that almost defectfree surfaces of a high quality can be produced in a repeatable way. The depths of significant and detectable damages are determined depending on the technique in question.     

Growth of bulk zinc chalcogenide single crystals from the vapour phase and their use for laser screens of projection colour television

Results on ZnSe, ZnSe_xS_1−x and ZnS crystal growing from the vapour phase up to 7.5 cm³ in volume are described. Crystals were grown on sapphire, ZnS, ZnSe_xS_1−x and quartz glass substrates without a contact of the growing crystal with a growth ampoule and using the molten tin as a heating medium. Large high-purity crystals with a density of etch pits of 10³ cm⁻² were obtained They exhibited an effective exciton luminescence and rather high radiation efficiency (30 ± 10% for ZnSe at T = 77 K). This made it possible to use these crystals for fabricating laser screens for a cathode ray tube. The main laser parameters obtained on a ZnSe screen at T = 80 and 300 K using a 75 keV electron beam excitation are presented. The light power output reached 0.8 W at T = 80 K; this allowed to obtain a 10 cd · m⁻² TV image of 1.5 × 2 m² in area.     

Investigation of radiation defects in electron irradiated Hg1−xCdxTe crystals using positron annihilation

The electron characteristics of defects in the initial and electron irradiated Hg_1−xCd_xTe (2–3 MeV, 10¹⁸ cm⁻², 300 K) crystals using the positron annihilation method have been investigated. The data of electric measurements are confirmed on connection of p-type conductivity with vacancy defects of metal sublattice initial crystals Hg_1−xCd_xTe. An analysis of correlation curves of irradiated crystals has shown a possibility of formation of associations of initial defects and radiation damages of vacancy type during radiation process. The presence of narrow component on correlation curves in the region of small angles is associated with formation of positronium states localized in the region of radiation defect complex of vacancy type. Identification of positron-sensitive defects with electrically active radiation induced ones has been carried out according to the results of isochronal annealing of irradiated crystals.     

Electrical Characterization of Irradiation plus Annealing – induced VAsZnGa Pairs in p-type GaAs (Zn) Crystals

Effect of fast electron irradiation (E =2.2 Mev, ϕ_c = 1 × 10¹⁶ el/cm²) and subsequent annealings (T = 150 to 350 °C, t = 10 to 600 min) of zinc-doped p-type GaAs crystals on the formation and dissociation of V_AsZn_Ga, pairs is studied. An analysis of the formation and dissociation kinetics of V_AsZn_Ga pairs permitted to find the diffusion coefficient of radiation-induced arsenic vacancies D(D = 1.5 × 10⁻¹⁸, 1 × 10⁻¹⁷ and 5 × 10⁻¹⁷ cm²/s at 150, 175 and 200 °C accordingly), their migration energy ϵ_m(ϵ_m = 1.1 eV), the binding energy of V_AsZn_Ga, pairs ϵ_b(ϵ_b = 0.5 eV), and also their dissociation energy ϵ_d(ϵ_d = 1.6 eV).     

Impurity band conduction effects in liquid phase epitaxial Te-doped GaP grown from tin solution

GaP layers were grown by liquid phase epitaxy from tin solution on semi-insulating GaAs substrates with various amounts of Te added to the melt (x_Te = 10⁻⁴ …︁ 3 · 10⁻²). The Sn and Te concentrations in the layers were determined by chemical analysis as function of x. An analysis of the electrical measurements shows that the carrier transport in the layers is essentially determined by impurity band conduction effects.     

Structure and features of the surface morphology of <Emphasis Type="Italic">A</Emphasis><Superscript>4</Superscript><Emphasis Type="Italic">B</Emphasis><Superscript>6</Superscript> chalcogenide epitaxial films

The structure and features of the surface morphology of Pb_{1 − x} Mn _x Se (x = 0.03) epitaxial films grown on freshly cleaved BaF₂(111) faces and PbSe_{1 − x} S _x (100) (x = 0.12) single-crystal wafers were investigated by molecular beam condensation and the hot-wall method. It is shown that the epitaxial films, in accordance with the data in the literature for other chalcogenides, grow in the (111) and (100) planes, repeating the substrate orientation. Black aggregates are observed on the film surface of the films grown. The results obtained are compared with the data in the literature and generalized for other chalcogenides: A ⁴ B ⁶:Pb (S, Se, Te); Pb_{1 − x} Sn _x (S, Se, Te); and Pb_{1 − x} Mn (Se, Te). It is established that the formation of black aggregates, which are second-phase inclusions on the surface of epitaxial films obtained by vacuum thermal deposition, is characteristic of narrow-gap A ⁴ B ⁶ chalcogenides.     

Crystal growth of PbTe and (Pb,Sn)Te by the bridgman method and by THM

Synthesis and growth of PbTe and (Pb, Sn)Te single crystals by the Bridgman method and by the Travelling Heater Method (THM) from Te-rich solutions are described. It is to be seen from comparative investigations that seeded THM growth reproducibly provides oriented single-crystalline ingots free of low-angle grain boundaries and with etch pit densities of 8–12 × 10⁴ cm⁻². All the materials were p-type with carrier concentrations from 1 to 2 × 10¹⁸ cm⁻³.     

TEM and X-ray investigations of defect structure of PbSnTe crystal

The Pb_0.8Sn_0.2Te single crystal grown by the Bridgman technique was examined by X-ray and TEM methods. The X-ray reflection topography revealed that the PbSnTe crystal consisted of monocrystallinic blocks with linear dimensions of 1–5 mm separated by low angle boundaries of tilt-twist character. “As grown” defects observed by TEM method have been identified as single perfect dislocations and dislocation pairs. A mean density of dislocations inside the crystal blocks was no more than 10³ cm⁻². Except “as grown” defects rows of mobile dislocations were observed. All of dislocations lines were characterized by the same type of Burgers vector, i.e. b = 1/2a〈110〉.     

Hyperfine structure of EPR spectra of Cr5+ ions in irradiated sodium dichromate crystals

EPR spectra are studied of X-irradiated sodium dichromate crystals grown from an aqueous solution by evaporation at 31°C. Doublet lines of EPR-absorption are attributed to the Cr⁵⁺ ions in the CrO₄³⁻ and CrO₃⁻ radicals resulting from radiation decomposition of Cr₂O₇²⁻ and being in the lattice in two unequivalent positions. Hyperfine structure caused by interaction of an unpaired electron with Cr⁵³ nucleus were observed both at liquid nitrogen and room temperatures. For the line, caused by CrO₄³⁻ radical, g_y and A_y directions coincide and angles both between A_x, g_x and A_z, g_z make up ∼ 25°. The spectrum is described by usual spin Hamiltonian for S = 1/2 with following parameters (T = 77 K): for CrO: g_z = 1.984, g_y = 1.970, g_x = 1.961, |A_z| = 8.2 · 10⁻⁴ cm⁻¹, |A_y| = 13.7 × 10⁻⁴ cm⁻¹, |A_x| = 36.1 · 10⁻⁴ cm⁻¹; for CrO₃⁻: g_z = 1.915, g_y = 1.975, g_x = 1.985, |A_z| = 32.2 · 10⁻⁴ cm⁻¹.     

Diffusion Phenomena during the heteroepitaxy of Ternary Compounds of the Type (AxB1–x)1–ΔC1+Δ

In heteroepitaxy of ternary compound systems of the type (A_xB_1–x)_1–ΔC_1+Δ has to be taken into account the occurrence of complex diffusion phenomena independent on the epitaxial method applied which cannot be considered within a quasi-binary system AC–BC. Based on the statements of thermodynamics of irreversible processes a model for the calculation of diffusion profiles, regarding the influence of the compound crystal composition x on the deviation from stoichiometry Δ, is presented. Concentration profiles calculated in accordance to this model show typical maxima and minima. – Tellurium distribution profiles determined on heterostructures of the type (Pb_1–xSn_x)_1–ΔTe_1+Δ /PbTe got by electron-probe microanalysis may be explained qualitatively within the presented model. With the EBIC-method additional p-n junctions at the position of the extrema in the tellurium distribution were found.