Influence of proton implantation on the properties of CuInSe2 single crystals (II)

Copper deficient p-type conducting CuInSe₂ single crystals were implanted with 40 keV protons in the fluence range from 2.5 · 10¹⁴ to 1.5 · 10¹⁶ cm⁻². Over the whole fluence range the implanted layers were n-type conducting which is ascribed to passivation of the acceptors due to copper vacancies and formation of donors by hydrogen atoms located at interstitial positions. The thermal stability of the conductivity changes due to proton implantation is limited to temperatures below 100 °C.     

Comparative optical absorption and photoreflectance study of n-type CuInSe2 single crystals

Optical absorption spectra in the photon energy range from 0.4 to 1.2 eV and photoreflectance spectra in the range of the fundamental edge are measured on n-type CuInSe₂ single crystals. Photoreflectance spectroscopy yields the true gap energy while the near-edge absorption spectra are dominated by acceptor–to–conduction band transitions, the acceptor ionisation energy being about 80 meV. Based on intrinsic defect chemistry considerations this acceptor is ascribed to copper vacencies.     

Influence of proton implantation on the properties of CuInSe2 single crystals (I). Ion channeling study of lattice damage

The lattice damage of p-type CuInSe₂ single crystals implanted with 10 keV protons in the fluence range from 2.5 · 10¹⁴ to 8 · 10¹⁵ cm⁻² was investigated using the Rutherford backscattering/channeling technique. At proton fluences up to about 2 · 10¹⁵ cm⁻² radiation annealing of the defects is observed which is ascribed to very high defect concentrations in the unimplanted samples. At higher fluences radiation damage occurs but the concentration of radiation induced defects ramains low. There are indications that selenium interstitials or defect complexes with selenium interstitials involved are stable defects at room temperature.     

Effect of the defect structure character in calcite single crystals on X-ray diffraction

The paper presents experimental results for the dependence of the integral intensity of anomalous transmission T_i and Laue reflection R_i of X-rays on the structural quality of calcite single crystals as obtained by a two-crystal spectrometer. The relation between X-ray dynamic and kinetic scattering as a function of the sample thickness, densities of perfect dislocations in perfect CaCO₃ crystals and of atom-vacancy complexes in calcite crystals with „background”︁ has been found. Distortions due to perfect grown-in dislocations in calcite are shown to exceed those produced in crystals with „background”︁. The latter appear to be more X-ray transparent. A comparison with results of twin layer thickening experiments on CaCO₃ crystals of different qualities again points to the different nature of these distortions. In CaCO₃ crystals with the dislocation density of up to 2 × × 10³ cm⁻², the X-ray scattering, in our experiments, was consistent with the dynamic diffraction theory, while at higher dislocation densities, the X-ray scattering markedly differs from it.     

Electron probe microanalysis of CuInSe2 and CuGaSe2 crystals

A correction procedure for the quantitative electron probe microanalysis of nonstoichiometric crystals in the system CuInSe₂–CuGaSe₂ is presented and applied to the analysis of the terminal members of the mixtures. In CuInSe₂ samples a precipitation of Cu₂Se takes place due to an evaporation of volatile compounds with a composition ratio In: Se = 2:3. A similar reaction was observed in the case of CuGaSe₂.     

The defect structure of ammonium sulphate single crystals

The defect structure of larger ammonium sulphate crystals, grown from aqueous solutions, has been studied by means of X-ray diffraction topography after Lang's method. Several types of dislocations were identified. Moreover it was found that no relationship exists between growth rate and dislocation density, which implies that crystal growth proceeds via two-dimensional nucleation. No difference was found in the defect structure of crystals grown from pure water solutions and from aqueous solutions with 10 – 20% glycerine as additive: In both cases neither growth bands nor sector boundaries were found. On the other hand, crystals grown in aqueous solutions contaminated with Mn²⁺ and Fe³⁺ revealed growth bands and for Fe³⁺ a mosaic-like structure.     

X-Ray study of the defect structure of PbTe single crystals

PbTe single crystals grown by different methods were thinned electrolytically and examined by X-ray transmission topography. The transmission topographs, first obtained of this material, reveal substructure, slip lines and single dislocations. The samples exhibit different structural perfection in dependence on the growth method. In crystals of relatively high perfection, slip lines are the striking feature of defect structure, caused by surface damage during mechanical preparation. The most perfect sample has a dislocation density of 10² to 2 ṁ 10³ cm⁻². No slip occurs, probably due to small dopant contents.     

Modeling of the defect structure in dislocation-free silicon single crystals

A mathematical model of the formation of primary grown-in microdefects on the basis of dissociation diffusion is presented. Cases of “vacancy-oxygen” (V + O) and “carbon-interstitial” (C + I) interaction near the crystallization front are considered for dislocation-free Si single crystals grown by the floating-zone and Czochralski methods. The approximate analytical expressions obtained by setting 1D and 2D temperature fields in a crystal are in good agreement with the heterogeneous mechanism of formation of grown-in microdefects.     

On the influence of nonstoichiometry on luminescent properties of CdGa2S4 single crystals

Results of a study of photoluminescence and thermoluminescence of cadmium thiogallate single crystals grown from the melt are presented. Effect of nonstoichiometry on the properties of samples is studied. Some assumptions about the nature of centres in CdGa₂S₄ compound are made.     

Modeling of defect formation processes in dislocation-free silicon single crystals

A new alternative model of the formation and transformation of grown-in microdefects in dislocation-free silicon single crystals is proposed. The basic concepts of the alternative mathematical model of the formation of secondary grown-in microdefects are considered. It is shown that vacancy micropores are formed in a narrow temperature range of 1130–1070°C. This is caused by a sharp decrease in the concentration of background impurity which does not form agglomerates (they arise in the temperature range of 1420–1150°C upon crystal cooling).     

Thermoelectric properties of indium sesquiselenide single crystals

Single crystals of δ-In₂Se₃ were prepared in the solid state laboratory at Qena-Egypt, by means of Bridgman technique. The temperature dependence of the thermal e.m.f. α in the temperature range from 205 K up to 360 K of In₂Se₃ was studied. The δ-phase In₂Se₃ sample appeared to be n-type. The ratio of the electron and hole mobilities are found to be μ_n/μ_p = 1.378. The effective masses of charge carriers are m = 1.3 × 10⁻³⁰, m = 8.27 × 10⁻³¹ kg for holes and electrons, respectively. The diffusion coefficient was estimated to be D_n = 3.37 cm²/s and D_p = 2.45 cm²/s for both electrons and holes, respectively. The mean free time between collision can be deduced to be τ_n = 70 × 10⁻¹⁶ s and τ_p = 8 × 10⁻¹⁴ s for both electrons and holes. The diffusion length of the electrons and holes are found to be L_n = 1.5 × 10⁻⁷ cm and L_p = 4.4 × 10⁻⁷ cm.     

Effect of ultrasound on the growth of semiconductor single crystals

Crystallography Reports - The influence of ultrasound on striations in InSb, GaAs, and Bi-Sb single crystals grown by the modified Czochralski method was studied. Ultrasonic waves with a frequency...     

Acoustical properties of single crystals of mercurous halides

Velocities of propagation of elastic waves along principal crystallographic directions in Hg₂Br₂ and Hg₂J₂ single crystals were measured using the pulse and phase-pulse techniques. The values obtained were used to calculate the components of the elastic tensors c_ik and s_ik, as well as the phase and group velocities of propagation of longitudinal and transverse waves in the (100) and (001) planes, and the angular deviation of acoustic energy flux from the direction of the corresponding wave normal. Knowledge of the anisotropy of the elastic properties of Hg₂X₂ crystals and of their change with the anion (X = Cl, Br, J) leads to deeper understanding of the character of bonds in the crystal lattice and points the way to a better utilization of technical properties of the crystals. — Minimum velocity of propagation of an elastic wave falls in the case of Hg₂J₂ to a value v [100] [11 10] = 0,25 · 10⁵ cm/s, what is the lowest value known among all crystals. Maximum angular deviation of acoustic energy flux — nearly 50° — is exhibited by the quasi-longitudinal wave in Hg₂J₂ crystals. On substituting the Cl⁻ ions with Br⁻ and J⁻ ions, the anisotropy of elastic moduli C₃₃/C₁₁ increases by nearly 80%. Different mechanisms contribute to vectorial dependence of the elastic properties along different crystallographic directions.     

Influence of substrate orientation on the electrical properties of CuInSe2 epitaxial layers on GaAs substrates

The electrical properties of CuInSe₂ epitaxial layers on (111)A-, (110)-, and (100)-oriented GaAs substrates are investigated. At substrate temperatures T_sub ≧ 820 K the p-type conductivity observed is governed by an acceptor state with an ionization energy of about 110 meV independent of the substrate orientation. At T_sub ≦ 770 K three different acceptor states are found in dependence on the substrate orientation: 390 meV for (111)A-, 110 meV for (110)-, and a very shallow acceptor for (100)-oriented substrates. A possible correlation between these acceptor states and intrinsic defects is proposed.     

Optical properties of helium implanted inp single crystals

Optical absorption spectra of helium implanted InP single crystals are measured in the photon energy range from 0.9 to 1.3 eV. It is found that helium implantation gives rise to exponential absorption tails below the fundamental edge. The absorption coefficients as well as the characteristic tailing energy increase with increasing fluence.     

Preparation and properties of ultratransparent NaCl single crystals

The preparation of up to 100 mm diameter single crystalline ingots of ultratransparent NaCl by injecting the reactive atmosphere is reported. The resulting material exhibits high optical quality and bulk absorption coefficient at 10.6 μm of 0.91 × 10⁻³ cm⁻¹, close to the intrinsic value, which makes it suitable for transmissive components in high-power CO₂ lasers.