Internal drift effects on the diffusion of Ag in CdTe

Anomalous diffusion profiles of Ag in single crystalline CdTe were observed using the radiotracer ¹¹¹Ag. The diffusion anneals were performed at 800 K under Cd or Te vapor and in vacuum with low Ag concentrations. The measured Ag profiles directly reflect the distribution of the self-interstitials and vacancies of the Cd sublattice and are the result of chemical self-diffusion which describes the variation of the deviation from stoichiometry of the binary crystal as a function of depth and time. It turned out that the spread of the Ag dopant essentially is determined by the drift of the charged defects within the electric field caused by the distribution of the extrinsic and intrinsic defects.     

Thermoelectric Effect Spectroscopy and Photoluminescence of High-Resistivity CdTe:In

Thermoelectric effect spectroscopy and photoluminescence techniques were used to study the defect levels in samples from three crystals of CdTe:In grown by the vertical gradient freeze method. The main goal of the investigation was to study defects, which strongly trap charge carriers or act as recombination centers in order to eliminate them from the technological process. The main difference among detecting and non-detecting samples was the absence of electron traps with a very high capture cross-section and energy 0.6 eV to 0.7 eV, which act as lifetime killers even at low concentrations. Recently published ab initio calculations show a complex of Te antisite and Cd vacancy within this energy range.     

Semi-insulating CdTe with a minimized deep-level doping

The possibility to prepare semi-insulating CdTe with a deep-level doping below the limit 10¹³ cm⁻³ demanded in detector industry is studied theoretically within quasi-chemical formalism. We show that proper thermal treatment, including low temperature (ca 200°C) dwell, allows fulfillment of this demand also in 7N or less purity materials. The procedure is demonstrated in Te-rich CdTe doped with a shallow donor. Its principle is based on enhanced defect selfcompensation, which affords at sufficiently low temperature extremely high compensation of shallow defects. New high-temperature transport data are used to refine on previous native defect properties for the modeling. The analysis of diffusion rates at lowered temperature approves the model for a real-time experimental verification.     

Influence of the intensity and duration of cyclic loading on the tribotechnical characteristics of steel

We analyze the results of evaluation of the influence of cyclic loading on the wear rate of 45 steel under conditions of unilateral sliding in contact with the counterbody made of the same steel. It is shown that the presence of both low and high levels of cyclic loads relative to the fatigue limit leads to a decrease in the tribotechnical characteristics of the investigated steel. In authors opinion, this is explained by the deterioration of the conditions of contact sliding caused by the fatigue damage to the surface layer. The periods of initial hardening, crack initiation, and its growth typical of pure fatigue are also present in the dependences of the wear rate on the number of loading cycles in the case of superposition of fatigue and friction.Translated from Problemy Prochnosti, No. 1, pp. 96–107, January–February, 2005.     

Time relaxation of point defects in p- and n-(HgCd)Te after ion milling

Time relaxation of the electrical conductivity σ(77 K) and Hall coefficient R_H(77 K) of the n-type layer created by ion milling is investigated in Hg vacancy-doped, As-doped, and In-predoped p-type, and In-doped n-type Hg_1−xCd_xTe (0.2 < x < 0.22) samples. We show that the n-type layer is formed, and the temperature-activated relaxation occurs in all cases. The annealing at 75°C results in a gradual degradation of the converted n-type layer and a back n-to-p conversion within 8 days. The existence of a high-conducting, surface-damaged region with a high-electron density (∼10¹⁸ cm⁻³) and a low mobility (∼10³ cm²/Vs) is confirmed, and its influence on the relaxation is studied.     

Chemical polishing of CdZnTe substrates fabricated from crystals grown by the vertical-gradient freezing method

Chemical polishing is a process of crucial importance in the manufacture of epiready substrates for molecular beam epitaxy (MBE) of high-quality HgCdTe layers. With the aim of fabrication of (211) CdZnTe substrates, we focused on the fundamental research of polishing processes with respect to reducing subsurface damage. Wafers of the orientation (211) were prepared from the as-grown crystals by a process flow including oriented slicing, several steps of mechanical polishing, and finally chemical polishing. In the prechemical polishing process, several free and bound abrasives were applied to reach the surface roughness close to 1 nm. The surface polishing treatment included testing of the surface quality after each polishing step. We used an interferometer profiler, which yields detailed surface maps. Within chemical polishing processing, we have looked for an optimum composition of etchant based on the bromine-methanol/ethylene glycol solution and adequate polishing pad. We studied the substrate surface quality dependence on the rotation speed of the plate, sample loading weights, and duration of polishing. Correlation between the final surface roughness and layer thickness removed was established. The chemical polishing with a very low concentration of Br-methanol/ethylene glycol solution was found to yield very good CdZnTe surfaces with a perfect flatness.     

Galvanomagnetic properties of CdTe below and above the melting point

Temperature dependence of conductivity and Hall coefficient R_H is measured by DC and AC methods at temperatures between 600–1180°C. Two experimental approaches are used.¹ Galvanomagnetic measurements at defined temperature and Cd or Te pressure are performed in solid samples in the whole field of stability of solid in the pressure-temperature (P-T) diagram.² Galvanomagnetic measurements define temperature both in solid and in liquid phase. The typical semiconducting character of and 1/|eR_H|, when both parameters increase with temperature, is observed also in the liquid. The negative sign of R_H is observed above 600°C within the whole region of stability of solid, both at Cd and at Te saturation, and R_H<0 both in solid and liquid. 1/|eR_H| reaches 5 10¹⁹ cm⁻³ at 1180°C and the corresponding Hall mobility is 20 cm²/Vs. Three slopes characterize the temperature dependence of a 0.7 eV in the solid CdTe below the melting point 1092°C and 4.6 eV in the liquid phase at 1092°C<T<1160°C. Above 1160°C, conductivity increases moderately with the slope 0.8 eV. The experimental data for solid CdTe are evaluated by a theoretical model, including electrons from both the central minimum (-point) and four satellite minima (L-point) of the Brillouin zone. Theab initio results fit our experimental data after small modifications very well.     

Differential thermal analysis of supercooling in CdTe

The supercooling of the melt before the start of crystal growth depends on the previous overheating of the liquid, stoichiometry of the melt, and cooling rate. Differential thermal analysis (DTA) scanning experiments were performed for different cooling rates under constant Cd vapor pressures, which were varied from 1 atm to 5 atm. The maximum cooling rate was 1 K/min and the minimum was 0.05 K/min. It was found that the degree of supercooling systematically decreases with increasing of Cd vapor pressure and near 4–5 atm practically approaches zero. This complex behavior could be explained by a structural alteration in the state of the CdTe melt during stepwise changing of its stoichiometry from Te- to Cd-rich.     

Effect of preliminary cyclic loading on wear resistance of steel 45

Results of tests on wear resistance of steel 45 in the initial state and with preliminary cyclic loading are presented and analyzed. It is shown that cyclic loading damages the surface layer of the material. This, in turn, increases wear and restricts for the tribosystem a range of loads at which normal mecahnochemical form of wear is realized. These changes are also investigated with surface layers removed.Translated from Problemy Prochnosti, No. 4, pp. 31–34, April, 1990.     

Glycidyl methacrylate-compatibilized poly(lactic acid)/hemp hurd biocomposites: Processing,crystallization, and thermo-mechanical response

Poly(lactic acid)-based biocomposites were developed with hemp hurd (Cannabis sativa L.) with grafting-based interfacial compatibilization. Poly(lactic acid) was extruded with hemp hurd and glycidyl methacrylate as the polymer/hurd interfacial compatibilizer, and injection molded. Interfacial compatibility between poly(lactic acid) and hemp hurd increased with grafted glycidyl methacrylate in comparison to the non-compatibilized control, as corroborated by scanning electron microscopy fractography and mechanical analysis, which showed increases in the glycidyl methacrylate-grafted 20% (w/w) hemp hurd/poly(lactic acid) biocomposite, retaining 94% of the neat polymer strength, with increases in crystallinity, and showing a range of thermo-mechanical properties desirable for rigid biocomposite applications.