IR-spannungsoptische Ermittlung züchtungsbedingter Eigenspannungen in Silizium

The growth conditions and the resultant defect structure are the cause of residual stresses in silicon single crystals. The field of residual stress is nearly axial symmetrically; tensile stresses are in the centre and compressive stresses are at the periphery. The field of residual stress adapts itself to crystal symmetry by plastic deformation during the growth or annealing processes. The tangential compressive stresses at the periphery are 25 kp/cm² for Czochralski-grown crystals (diameter 36 mm, etch-pit density 5 · 10³ cm⁻²) and about 70 kp/cm² for crystals grown by the floating zone technique (diameter 28 mm, etch-pit density 3 · 10⁴ cm⁻²). Dislocation free crystals are almost free of residual stresses.     

EPR-spectrum of irradiated potassium dichromate single crystals

EPR-spectra of X-irradiated potassium dichromate crystals are studied at various temperatures from RT to LNT. The most intensive lines are interpreted as due to radicals CrO₄³⁻ (A-lines) and CrO₃⁻ (C-lines), resulting from Cr₂O₇ owing to X-irradiation. Hyperfine structure of C-line, due to interaction of unpaired electron with Cr⁵³ nucleus, occurs at low temperatures, and new unobserved earlier Q-lines appear near-by C-line. The spectrum may be described by usual spin Hamiltonian for S = 1/2 with following parameters: for A-line gz = 1.9841, gy = 1.9685, gx = 1.9592; for C-line gz = 1.9148, gy = 1.9671, gx = 1.9886, |Az| = 30.53 · 10⁻⁴ cm⁻¹, |Ax| = 10.62 · 10⁻⁴ cm⁻¹, |Ay| = 6.62 · 10⁻⁴ cm⁻¹.     

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.     

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.     

Nature of radiation defects in synthetic quartz according to the small-angle neutron scattering data

The supraatomic structure of single crystals of synthetic quartz in the initial state with a dislocation density of 570 cm^?2 and after irradiation in the VVR-M reactor at the Petersburg Nuclear Physics Institute with fast neutrons having the energy E _n > 1 MeV in the range of fluences F _n = 7.7 × 10¹⁷ ?2.1 × 10²⁰ neutrons/cm² has been studied by small-angle scattering of thermal neutrons. It is established that fast neutrons form point, linear, and volume lattice defects throughout the entire sample volume. Large-volume structures (nuclei of the amorphous phase) in quartz, reaching ～100 nm in size, occupy a small total volume (～1.5%) even at the maximum fluence 2.1 × 10²⁰ neutrons/cm². The majority of damage is related to the point defects with the radius of gyration of 1–2 nm and linear defects, which give comparable contributions up to several percent.     

TEM Studies of Er+ – implanted CdTe

The structure and the depth distribution of radiation damage caused by erbium implantation (E_i = 100 keV, D = 5 × 10¹⁵ cm⁻², T_i = LNT) in 〈111〉 cadmium telluride have been investigated by means of planar-view and cross-sectional TEM techniques. It is found that the implantation disturbes the CdTe target up to the depth well-beyond the calculated projected range (that is ≳ × 5R_p). The resulting damage structure consists of well-defined defects: precipitates, stacking faults, dislocation loops, and dislocation networks, which appear to be segregated with depth forming a sequence of homogeneously faulted zones. This characteristical and deep damage is suggested to be formed on dynamic annealing in response to internal stresses (caused by lattice parameter mismatch) which are high enough to produce plastic relaxation with dislocation generation and slip. This study is aimed at describing the ion-implantation-induced damage in single crystal cadmium telluride caused by Er⁺ ions by means of transmission electron microscopy.     

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.     

Die Herstellung von einkristallinen Dünnschichten aus Halbleitern mit ausgeprägter Anisotropie durch gerichtete Kristallisation der Schmelze zwischen zwei Substraten

Investigation of monocrystalline thin layers (5 to 150 μm in thickness) of Te and CdSb orientedly grown between two substrates. The form of the solidifying front strongly influencing crystal perfection can be controlled. Thin layers grown with velocities < 0.25 cm · min⁻¹ are monocrystalline with etch pit densities of 6 · 10² cm⁻². The electrical quantities R_H, σ and α of the layers are nearly identical with those of bulk material. Doped monocrystalline CdSb layers had a minority carrier concentration of ∼ 10¹⁴ cm⁻³ at 77°K.     

Small-angle neutron scattering study of radiation-induced defects in synthetic quartz

The supraatomic structure of single crystals of synthetic quartz was studied by thermal neutron small-angle scattering in the initial state (dislocation densities 54 and 570 cm⁻²) and after irradiation in the WWR-M reactor (Petersburg Nuclear Physics Institute) by fast neutrons with energies E _n > 0.1 MeV at fluences F _n = 0.2 × 10¹⁷ −5 × 10¹⁸ neutrons/cm². It is established that fast neutrons form point, linear, and volume defects in the lattice throughout the entire volume of a sample. Large-volume structures—amorphous-phase nuclei—reach sizes of ∼100 nm in quartz, while occupying a small total volume of ∼0.3% even at the maximum fluence 5 × 10¹⁸ neutrons/cm². The main fraction of the damaged volume (up to 5%) corresponds to point (with a radius of gyration of 1–2 nm) and linear defects, giving a comparable contribution (∼1–4%). The extended linear structures with a radius of 2 nm, even at a moderate fluence of 7.7 × 10¹⁷ neutrons/cm², have a significant total length per volume unit (∼10¹¹ cm/cm³) and can form a connected network with a cell ∼30 nm in size in the sample. Foreign atoms and molecules can migrate through channels of this network.

     

Preparation of InN epitaxial layers in InCl3?NH3 system

The epitaxial growth of InN by the open tube flow method using the interaction of InCl₃ and NH₃ is discussed. The influence of various technological parameters on the process and structure perfection of the epitaxial layers, grown on the single crystal (0001)-oriented sapphire substrates is considered. The main kinetic dependences of the process are plotted and discussed. InN epitaxial layers were mosaic and n-type with electron concentration 2 · 10²⁰–8 · 10²¹ cm⁻³ and mobilities 50-35 cm²/V · s, respectively.     

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.     

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.     

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 the nature of point defects in in Te-doped gallium antimonide

Precision lattice constant and density measurements held on gallium antimonide single crystals grown from stoichiometric melts showed that doping of such crystals with Te lead to the intensification of Ga-supersaturated solid solution decomposition process with initial Frenkel defect (Ga_i + V_Ga) production. It is supposed that Te_sb — simple donors form complexes with V_Ga which are believed to be acceptors. Doping of GaSb with Te up to the levels above 2 · 10¹⁸ cm⁻³ leads to partial decomposition of GaSb(Te) solid solution supersaturated with Te.     

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.     

Crystal Structure of a Complex of Sarcosine with Barium Chloride

Single crystals of sarcosine barium chloride tetrahydrate were crystallised from a saturated aqueous solution containing stoichiometric amounts of sarcosine and barium chloride, in 2: 1 proportion. The intensity data were collected using a CAD-4 diffractometer with graphite monochromated MoKα radiation. The crystal data are as follows: a = 7.235(1) Å, b = 10.668(4) Å, c = 15.686(3) Å, V = 1210.7 ų, F.W. = 369.33, d_expt, = 2.02 g · cm⁻³, d_calc = 2.026 g · cm⁻³, Z = 4 and the space group is P2₁2₁2₁. The structure has been solved to an R value of 0.02 for all the 1239 reflections with I > 2σ(I). The sarcosine molecule exists as zwitterion in the structure. The barium ion is found to have 10-fold coordination with nine oxygens and a chlorine taking part in coordination. All the water oxygens and chlorines take part in hydrogen bonds except carboxyl oxygens.     

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.     

Density and mobility of anti-frenkel defects in SrF2 crystals

By fitting the theoretically calculated temperature-dependent conductivity σ to the measured dependencies log σT ÷ 1/T the following parameters have been determined: free formation enthalpy of anti-Frenkel defects g_AF = 2.05 eV – 6.35 kT; mobilities of F⁻ion vacancies F and interstitials F: v_νT = 600 exp (-0.70 eV/kT) cm² K/Vs, v_iT = 1.1 · 10⁴ exp (-0.93 eV/kT) cm² K/Vs. — The free association enthalpies of complexes consisting of single foreign ions (Sc³⁺, Y³⁺, La³⁺, Sm³⁺, Li⁺, K⁺, Na⁺, O⁻) and the charge-compensating defect were obtained. The vibration frequency of F⁻ ions in the neighbourhood of F and F is changed by a factor of 2.6 and 0.6, respectively.     

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.     

The effect of temperature on the raman spectra of strontium formate dihydrate single crystals

The temperature dependence of the polarized Raman Spectra (3000 cm⁻¹ – 10 cm⁻¹, between 293 K and 10 K) of Sr(HCOO)₂ · 2H₂O(2D₂O) and partially deuterated samples is reported. From the analysis of the internal and external modes associated with water molecules and formate ions a phase transition is deduced. This is interpreted on the basis of the positional disorder of the hydrogen atoms, situated in non-equivalent lattice positions at low temperature.