Zur Realstruktur von Ga1–xInxAs LPE-Schichten

Ga_1–xIn_xAs epitaxial layers (0.02 ≦ × ≦ 0.12) are grown on (111)-oriented GaAs substrates from nonstoichiometric melts. The etch pit densities – determined by chemical etching – yield values between 2 · 10⁵ cm⁻² and 3 · 10⁷ cm⁻² and were found to be dependent on composition, layer thickness and cooling rate. X-ray topography of cleaved {110}-planes gives information on layer quality and indicates the existence of stress in the substrate lattice near the heterojunction. The validity of Vegard's law in the investigated concentration range was confirmed by X-ray determination of the lattice constants. The half width of double crystal spectrometer rocking-curves, the epd and the relative intensity of photoluminescence show similar dependence on the composition of the mixed crystal layers.     

The growth of high-quality MCT films by MBE using in-situ ellipsometry

The ellipsometry and RHEED study of high-quality MCT films grown on (112)- and (130) CdTe and GaAs by MBE was carried out. The dependence of the ellipsometric parameter ψ on MCT composition is evaluated. It was shown that such parameters as growth rate, the surface roughness, initial substrate temperature, and film composition may be measured by the in-situ ellipsometry. The appearance of surface roughness was observed in the initial stage of MCT growth under various compositions (x_CdTe = 0 ÷ 0.4). The further growth at optimum conditions leads to the smoothing of the surface and supplies us with high-quality MCT films. The concentration, mobility, and life time of carriers in MCT films were respectively: n = 1.8 × 10¹⁴ ÷ 8.2 × 10¹⁵ cm⁻³, μ_n = 44000 ÷ 370000 cm² V⁻¹ s⁻¹, τ_n = 40 ÷ 220 ns; p = 1.8 × 10¹⁵ ÷ 8.4 × 10¹⁵ cm⁻³, μ_p = 215 ÷ 284 cm² V⁻¹ s⁻¹, τ_p = 12 ÷ 20 ns.     

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.     

Pressure Dependence of C–V Curve for Ferroelectric PbTiO3 Thin Films Prepared by RF Multi-target Magnetron Sputtering

Lead titanate thin films were prepared in-situ by RF magnetron sputtering method in the substrate temperature region of 550 °C ˜ 650 °C using Ti and Pb metal targets and oxygen gas. The films deposited at 650 °C for 60 min – when the applied power to the Ti and Pb target and deposition pressure were 200 W, 40 W, and 1.8 × 10⁻² Torr, respectively — had stoichiometric composition ratio and shown X-ray diffraction patterns of tetragonal structure like that of the powder. For the application to the piezoelectric field effect transistor (PI-FET), the substrate of SiO₂ (50 nm)/p-Si(100) was used. Leakage current density of the thin film was 7 × 10⁻⁸ A/cm² at 100 kV/cm, dielectric breakdown voltage was 1.8 MV/cm, and so it showed high insulator characteristics. Capacitance-voltage curve was measured as a function of pressure. The variation width of the capacitance was 6.5 pF at bias voltage of –4 volts, and the value increased linearly according to the pressure up to about 6 kgf/cm², and was saturated at the pressure of 8 kgf/cm².     

Investigation of the structure of thin rhenium films

The phase composition of thin rhenium films as depending on deposition conditions has been studied. In films deposited at a pressure of 10⁻⁵ torr impurity phases with simple cubic and hexagonal lattices were found. In films evaporated at a pressure of 10⁻⁸ torr only an hep phase equilibrium in bulk samples is formed. It has been concluded that in thin rhenium films no transitions to a fcc phase occurs. In the present work the dependence of thin film phase composition was investigated as a function of film thickness (∼5–500 Å), deposition rate (∼0.1–10 Å/sec) and substrate temperatur (∼ 20–450°C). The films were deposited on NaCl single crystals at a pressure of 10⁻⁵ torr (oil diffusion pump evacuation) an 10⁻⁸ torr (“Orbitron”-type pump evacuation). The measurement of film thickness was conducted by the optical interference method.     

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.     

Calculation of Diffusion-limited Growth of Hg1−x Cdx Te Epilayers on CdTe from Te-rich Melts by Step-Cooling LPE

Calculations of layer thicknesses and composition profiles in Hg_1−xCd_xTe layers on CdTe substrates for the growth from Te-rich melts have been carried out for liquidus temperatures of 460 °C, 480 °C, and 500 °C. This has been made on the basis of the multicomponent diffusion model of SMALL and GHEZ and the solid-liquid phase relation of BRICE . It could be shown that growth velocity increases only slightly with rising liquidus temperature. On the other hand, the interdiffusion velocity of Hg and Cd in the solid increases remarkably at a higher temperature. Therefore, to get layers with a constant x-value a higher supersaturation of the melt is necessary. The x-value decreases with rising supercooling by about 0.003 K⁻¹. To demonstrate the thermodynamically and kinetically advantageous properties of CdTe as substrate material, comparative calculations for a “hypothetical” HgTe substrate have been involved.     

Germanium Incorporation in Ga1–xInxAs LPE Layers and GaAs Bulk Crystals

Atomic absorption spectroscopy (AAS) is used to determine the Ge concentration in Ga_1–xIn_xAs and GaAs. The orientation dependence of Ge incorporation in (111)A-and (111)B oriented samples has been studied. The distribution coefficients for both the orientations were determined to be k_Ge^(111)A = 2.6 · 10⁻² and k_Ge^(111B = 1.4 · 10⁻² for Ga_1–xIn_xAs with 0 ≦ x ≦ 0.13. The differences between the two orientations are explained with the aid of the band bending model. Doping gradients in thick epitaxial layers and along crystal length of polycristalline TGS-grown GaAs ingots have been investigated too. In Ga_1–xIn_xAs layers any Ge concentration gradient couldn't be observed, but in TGS compact crystals Ge concentration increases with crystal length because the melt composition changes significantly during solidification. The results are compared with those of electrical measurements.     

Infrared optical properties of Cu1−xLixSe2 thin films

Infrared absorption spectra of Cu_1−xLi_xInSe₂ thin films are measured at room temperature in the wavenumber range from 100 to 600 cm⁻¹. The spectra exhibit two absorption bands in the wavenumber ranges 200–210 cm⁻¹ and 330–355 cm⁻¹ which are ascribed to vibrational modes due to In Se and Li Se vibrations, respectively. The influence of the phase transition from the chalcopyrite structure to the β-NaFeO₂ structure in the composition range x = 0.5–0.6 on the vibrational characteristics is established and discussed.     

A study of the Growth-Temperature-dependent Surface Morphology in InSb Liquid Phase Epitaxy

InSb LPE layers were grown on (111) InSb substrates, their phase diagram and growth rates studied. The InSb activity coefficient α(T), determined by fitting the experimental data, had a value of 2556–11.11 · T cal · mole⁻¹. The terraces on the surface were reduced by increasing the temperature to 350 °C. Hall measurements of InSb/CdTe heterostructure failed due to the high Te segregation. The carrier concentration of these InSb epilayers, however, was determined by C-V measurements with values between 7.5 · 10¹⁴ cm⁻³ and 5 · 10¹⁵ cm⁻³.     

Investigations for Sn diffusion in Pb1−xSnxTe and PbTe

By annealing Pb_1−xSn_xTe and PbTe isothermally in a quartz ampoule Sn diffused from Pb_1−xSn_xTe into PbTe. The profiles obtained have been investigated by means of an electron beam microanalyser, and the coefficients of diffusion have been determined at various temperatures. The diffusion of Sn can be explained by the expressions: D_PbSnTe = 1.5 · 10⁻¹ exp (−1.8 eV/kT) cm² s⁻¹ (0,14 < x < 0,18) D_PbTe = 5,5 · 10⁻⁴ exp (−1.5 eV/kT) cm² s⁻¹. N-type layers are observed at the surface of Pb_1−xSn_xTe specimens.     

Dislocation density in InxGa1–xAs films grown on GaAs substrates with intermediate buffer layer InGaAsP of variable composition

In_xGa_1–xAs films with x = 0.03 and 0.05 were grown from an In Ga As P liquid phase. Because of high value of distribution coefficient of P we have heterojunction GaAs In_yGa_1–yP_zAs_1–x–In_xGa_1–xAs. The influence of Phosphorus atom fraction (X_p) in liquid phase on dislocation density in the top In_xGa_1–xAs layer was studied. It was found that dislocation density (N_d) as a function of X_p is a curve with some minima. The minima of N_d for substrates of (111) A and (111) B orientations are observed in the different intervals of X_p axis. — The width of N_d minimum is decreased if the substrate is misoriented from the (111) plane. — It was supposed that the clusters exist in the liquid phase. On the basis of this assumption one can explain the influence of substrate position over or under the melt on the film perfection. The diameter of these clusters is estimated to be about 500 Å.     

The molecular and crystal structure of 2-oxo-1-pyrrolidine-acetamide

C₆H₁₀N₂O₂, P1 , a = 6,607(2) Å, b = 8,538(2) Å, c = 6,392(2) Å, α = 102,43(2)°, β = 91,11(2)°, y = 79,82(2)°, V = 349,1 ų, Z = 2, D_m = 1,36 g × cm⁻³, D_x = 1,35 g × × cm⁻³, MoKα radiation, λ = 1.71069 Å, μ(MoKα) = 1.11 cm⁻¹. The structure was solved by direct methods. The parameters were refined by full matrix least squares technique to a final R = 0.088 for 834 reflections with ∥F₀∥ > 4σ(F₀). The dihedral angle between the least-squares plane through the pyrrolidine ring and that through the acetamide group is 90.4°. The N H … O hydrogen bonds connect molecules to form bands parallel to the z axis.     

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.     

Phase Equilibrium of the Ga–Al–Sb system

Employing the method of liquid-phase epitaxy (LPE) solid-solutions of Ga_1–xAl_xAl_xSb (0 ≦ x ≦ 0.8) have been obtained. The dependence of Sb solubility on Al concentration in the liquid phase at 403°C, 452°C, 500°C has been established. The dependence of AlSb concentration in the solid phase on the composition of the liquid phase has been investigated at 452°C. Using the chemical constants equilibrium method, the phase equilibrium of the Ga–Al–Sb system in the region of liquid phase composition near the Ga-rich corner of the phase diagram has been calculated. The comparison of experimental and calculated data for the liquid and solid phases shows their agreement within the limits of experimental error.     

EPR and Optical Absorption Spectra of Cr3+ Ions in Lithium Sulphate Single Crystals

Optical absorption and EPR spectra of Li₂SO₄ · H₂O crystals doped with Cr³⁺ are studied at liquid nitrogen temperature. The bands are found in absorption spectra with maxima about 17000, 23 800 and 37 200 cm⁻¹, assigned to the ⁴A₂ → ⁴T₂, ⁴A₂ → ⁴T₁ and ⁴A₂ → ⁴T₁ (⁴P) transitions, respectively. The crystal field theory parameters were determined and appeared to be as follows: Dq = 1700 cm⁻¹, B = 667 cm⁻¹, C = 3002 cm⁻¹. The lines resulting from Cr³⁺ ions are found in EPR spectra. All lines are doublets, which is indicative of presence of two magnetically unequivalent centre positions, and have the hyperfine structure resulting from interaction of the unpaired electron spin with Cr⁵³ isotope nucleus. Centres are oriented in such a way, that z-axes, corresponding to two centre positions, are situated at both sides of a-axis at an angle of about 3°. Spin Hamiltonian parameters were found as follows: g_x = 1.985, g_y = 1.984, g_z = 1.988, D = 0.130 cm⁻¹, E = 0.016 cm⁻¹, |A| = 17.8 · 10⁻⁴ cm⁻¹.     

Structure and electrical resistance of thin scandium films (III). Study on electrical properties

The specific resistance-thickness of ScH_x (vacuum 10⁻⁵ to 5 · 10⁻⁶ Torr) and Sc films (vacuum 1 · 10⁻⁸ to 3 · 10⁻⁸ Torr) relationships have been obtained by keeping a record of a film resistance directly in the course of condensation. The results are discussed according to the theory FUCHS -SONDHEIMER (ScH_x, Sc) and MAYADAS -SHATZKES (Sc) assuming a diffuse scattering of the carriers (P = 0) on the external surface of the films. A mean free path of the current carriers is 188 to 355 Å (T ⋍ 300 K) for ScH_x and 400 Å with grain-boundary scattering parameter from 0.1 to 0.3 for Sc. The temperature dependence of specific resistivity of Sc films was obtained in the interval from 300 to 650 K during the annealing in vacuum 5 · 10⁻⁹ Torr.     

Surface Chemical Bonding States and Ferroelectricity of Pb(Zr0.52Ti0.48)O3 Thin Films

The surface chemical bonding states and the ferroelectric properties of sol‐gel deposited lead zirconate titanate [Pb(Zr_0.52Ti_0.48)O₃, PZT] thin films coated on (111)Pt/Ti/SiO₂/Si substrates were investigated. X‐ray photoelectron spectroscopy (XPS) was used to determine the oxidation state of the surface and the chemical composition as a function of depth in ferroelectric PZT thin layers. Values for the dielectric constant and dissipation factor at 1 kHz for the 300 nm‐thick film were 1214 and 0.014 for the film annealed at 520 °C, and 881 and 0.015 for a film annealed at 670 °C. Measured values for the remanent polarization (P_r) and coercive field (E_c), from polarization‐electric field (P‐E) hysteresis loops biased at 10 V at a frequency of 100 Hz, were 16.7, 14.4 μC/cm² and 60, 41.7 kV/cm for 520 °C and 670 °C. The leakage current density (J) was 72 and 96 nA/cm² at an applied field of 100 kV/cm. It was found that the bonding states of lead and oxygen in the surface regions could be correlated with the ferroelectric properties of the integrated thin layers.     

Scandium thin films-structure and electrical resistance (I). A study on films obtained in a vacuum of 10−5 up to 10−6 Torr

A structure as well as a specific electrical resistance of scandium films having a various thickness (300 up to 2800 Å) obtained at a condensation rate: w⋍ 1 up to 155 Å/s have been studied in the present work. Depending on condensation conditions in films a hydride ScH_x, h.c.p. — Sc, or ScH_x + Sc alternatively, is formed, a phase containing a distorted hexagonal lattice evolving into the ScH_x over a period of a few hours. The ScH_x and h.c.p-Sc change to Sc₂O₃ when annealed in a vacuum of 5 · 10⁻⁵ Torr at a T ≈ 800°C, while in a vacuum of 3 · 10⁻⁸ Torr a change to h.c.p.-Sc with negligible inclusions of oxidic Sc₂O₃ particles takes place. Formation of oxide is observed also when heating the films with an electron beam directly in a microscope under vacuum of ∼ 8 · 10⁻⁵ Torr. The specific electrical resistance ϱ of the film just after a condensation has taken place is approximatly by an order higher as against the ScH_x- and h.c.p.-Sc solid specimens. An irreversible gain in said resistance is observed while holding at a room temperature or annealing in a vacuum of 5 · 10⁻⁵ Torr, this being associated with absorption of H₂, O₂ and, possibly, of water steam, and then with formation of Sc₂O₃. Annealing in a vacuum of 5 · 10⁻⁸ up to 10⁻⁷ Torr involves a temperature relationship for ϱ of an intricated nature, this being accounted for by a structure transition as follows: A diode-effect diminishing with a temperature rise is observed in annealed films.     

On the Density of Synthetic Glasses in the System Soda Melilite – Gehlenite/Ákermanite

The solid density has been determined at 25°C by hydrostatic weighing along the binary systems Sm–Ge₅₀Åk₅₀ and Sm–Ge₇₀Åk₃₀. The molar volume V decreases linearly with increasing mole fraction of Ge_mÅk_n, x_B, according to δV/δx_B = −5.08 cm³ mol⁻¹ and −4.40 cm³ mol⁻¹ for Ge₅₀Åk₅₀ and Ge₇₀Åk₃₀, respectively. The results enable the molar fraction x_B to be determined from density measurements with an absolute error of ±5 mol%.