ZINC SELENIDE SINGLE-CRYSTAL GROWTH BY CHEMICAL-TRANSPORT REACTIONS

ZnSe single crystals were grown by closed-tube chemical vapour transpo rt at temperatures below 800 degrees C. In the ZnSe-I-2 transport syst em studies have been performed to elaborate the influence of different heat and mass transport mechanisms on effects of nucleation and cryst al growth. The transport of ZnSe, which is assumed to be composed of d iffusion, Stefan flow and convection, was calculated by a numerical mo del. In the total pressure range between 0.5 and 2 atm, qualitative ag reement has been found between the experimental transport rates and th e theoretical ones. Experimental variables were the system pressure, t emperature conditions, the concentration of the transport agent, and t he aspect ratio of the ampoule. In contrast to convection controlled s ystems, mainly diffusion-limited mass transport reduces nucleation den sity and favours the growth of large ZnSe crystals of good crystallogr aphic perfection.