A large diameter single crystal of germanium has been required for infrared optics, lenses and optical windows. A large boule of single crystal in a 130 mm diameter is obtained by heat exchange method in place of the Czochralski method. The optical properties were evaluated by IR-interferometry. The deviations of refractive indices are estimated to be below 1O^<-4> order in whole aperture. By further considering the heat exchange mechanism of the crucible, even larger scale single crystals will be produced by this technology in the near future.
ZnSe bulk single crystals used for the substrate of blue laser device fablication were grown by sublimation method and the quality was evaluated by photolumincscence spectra (PLS). Starting from high purity elements Zn and Se, supplied form company, high purity ZnSe crystals, comparable to the highest one reported so far were grown by this method. In order to obtain the n-type crystals with low resistivity, sublimation grwoth was performed also under controlled vapor pressure of ZnI_2 or ZnCl_2 and it was confirmed that iodine or chlorine is incorporated quantitatively in grown crystal by this method.
Crystals of CuAlSe_2, one of the promising materials for optical or optoelectronic devices in blue color wavelength region, were grown by chemical vapor transport (CVT) method using iodine as a transport agent. An optimum condition for growth of large stoichiometric single crystals was determined by adjusting growth parameters such as an iodine concentration (D_1), source temperature (T_s), growth temperature (T_c) and temperature difference (ΔT) between T_s and T_c. A large single crystal with a well-developed (112) face with a typical dimension of 9×5×0.45mm^3 was obtained under the conditions of T_s =1223-1263K, ΔT=50K and D_I=2-3mg/cm^3. The transport rate in the present case is limitted by a condensation process of gas molecules in the vapor phase. Iodine with a concentration of several hundred ppm was found to be incorporated into crystals obtained. The incorporated iodine is expected to occupy mainly the Se site, a part of which occupies the nearest sites of Cu vacancy, forming the so-called S-A like complex center. Iodines which substitutes the Se site to form the complex center seem to affect the electrical and optical properties of grown crystals. Observed high p-type resistivity can be attributed to compensation of Cu-vacancy originated acceptor by iodine donor at the Se site. Two broad photoluminescence peaks observed at 1.82 and 1.96 eV was also related to the complex defects.
It is well-known that the type of grown-in defect in single crystals of silicon depends on the ratio of v/G_o (v;growth rate, G_o;axial temperature gradient of the crystal) and that the vacancy-type defect appears above a critical v/G_o, and the self-interstitial type defect appears below this critical ratio. In order to explain the defect behavior by solving the diffusion equations of point defects, it is necessary to know the values of diffusion coefficients and equilibrium concentrations of them. However, the reported values of these quantities scatter widely. We have investigated the necessary conditions which are able to explain the defect behavior. It is shown that the necessary conditions are as follows. 1) D_<v,mp>E_v^f>D_<I,mp> E_I,^f, 2)D_<V,mp>×E_v^f>6×10^<-4> eV・cm^2/sec, 3) E_V^m>E_I^m, E_V^f>E_I^f, 4) The contribution of pair annihilation to the point defects concentration is small near the melting temperature. Where D_<v,mp>,D_<Imp>, diffusion coefficients at melting temperature, E^f, formation energy, E^m; activation energy of diffusion, V and I; vacancies and self interstitials.
Dependence of surface tension of molten silicon on temperature, oxygen partial pressure in ambient argon gas atmosphere and oxygen concentration in molten silicon have been determined at temperatures from 1693 K to 1773 K and in the range of oxygen partial pressure from 4×10^<-22> MPa to 6×10^<-19> MPa by sessile drop method under precisely controlled oxygen partial pressure using oxygen sensor which was composed of solid electrolytes, Zr0_2・CaO. The surface tension steeply decreases with increasing the oxygen partial pressure. The extent of the surface tension reduction decreases with increasing temperature. Relations between the surface tension and the oxygen partial pressure and oxygen concentraton in the silicon melt are fairly described with Szyskowski's equation. The temperature coefficient of the surface tension is minus and the absolute value of the temperature coefficient decreases with increasing the oxygen partial pressure. Absolute value of the temperature coefficient at constant oxygen partial pressure is smaller than that at constant oxygen concentration in the silicon melt. The above oxygen dependence of temperature coefficient of the surface tension are fairly described with the equations which were derived thermodynamically based on the assumption of the oxygen equilibrium between gas and molten silicon and the equilibrium of oxygen adsorption on the surface of molten silicon.