Electrical and mechanical properties of vapour grown gallium monotelluride crystals

The physical vapour deposition （PVD） of gallium monotelluride （GaTe） in different crystalline habits was established in the growth ampoule, strongly depending on the temperature gradient. Proper control on the temperatures of source and growth zones in an indigenously fabricated dual zone furnace could yield the crystals in the form of whiskers and spherulites. Optical and electron microscopic images were examined to predict the growth mechanism of morphologies. The structural parameters of the grown spherulites were determined by X-ray powder diffraction （XRD）. The stoichiometric composition of these crystals was confirmed using energy dispersive analysis by X-rays （EDAX）. The type and nature of electrical conductivity were identified by the conventional hot probe and two probe methods, respectively. The mechanical parameters, such as Vickers microhardness, work hardening index, and yield strength, were deduced from microindentation measurements. The results show that the vapour grown p-GaTe crystals exhibit novel physical properties, which make them suitable for device applications.

^(60)Co Gamma Irradiation and Annealing Effects on Transport Properties of Antimony Telluride Platelets Grown by Physical Vapor Deposition

Physical vapor deposition method was employed to deposit antimony telluride （Sb2Te3） crystals in a dual-zone furnace. The microstructure, surface topography and composition of samples were characterized using X-ray diffraction, atomic force and scanning electron microscopy. Seebeck coefficient （Sic）, electrical conductivity （σ⊥c） as well as power factor （PF） were enhanced for pure Sb2Te3 samples upon annealing, and the samples annealed at 473 K exhibited the highest PF of 3.16 × 10^-3 W m-1K-2 with an enhancement of 22% in the figure of merit （Z）. When the delivered dose of 60Co gamma radiation was increased from 0 to 30 kGy in the stoichiometric crystals, σ⊥c decreased due to the decrease in mobility. As a result of the increase in S, PF and Z improved by 12.11 and 13.7%, respectively, in the 30 kGy gamma- irradiated crystals. Both RH （BIIc） and S⊥c were positive, suggesting that the prepared Sb2Te3 crystals retained the p-type semiconductivity after these treatments.

Gamma Irradiation Effects in InBi_(0.8) Te_(0.2) Crystals Grown by Horizontal Directional Freezing

The high-energy gamma-ray irradiation treatment using Co-60 isotope offers the possibility of engineering mechanical and optoelectronic properties of In Bi0.8Te0.2crystals. Tellurium-doped indium bismuthide（In Bi） crystals were prepared by horizontal directional freezing technique. Dose-dependent modifications in structure, composition and surface topographical features have been analyzed by X-ray powder diffraction, X-ray energy-dispersive analysis, transmission electron and atomic force microscopy, respectively. Dielectric constant and dielectric loss were found to increase with the cumulative dose of radiation, and a shift in the ferroelectric transition temperature（Tc） from 405 to 410 K was observed for25 k Gy. Upon irradiation, there is an enhancement in microhardness（HV）, yield stress（ry） and stiffness constant（C11）.The optical transmittance was decreased by 12.45%, resulting in a reduction in the optical band gap from 0.210 e V to0.198 e V. These results indicate the suitability of In Bi0.8Sb0.2crystals for low-wavelength infrared applications.