Crystals were grown by using the physical vapour transport technique under horizontal and vertical (stable or unstable) configurations. Secondary ion mass spectroscopy and photoluminescence methods were applied to the as-grown samples in order to map the distributions of Si, Fe, Cu, Al and Li (or Na) impurities; as well as that of the Zn vacancy. In horizontally grown crystals, segregation of Si, Fe, Al and VZn was observed in the direction of gravity. In stable vertically grown crystals, the segregation of the point defects was radially symmetrical. No pattern was apparent in the distributions in unstable vertically-grown crystals. The segregation was attributed to buoyancy-driven convection in the vapour phase.

Point Defect Distributions in ZnSe Crystals - Effects of Gravity Vector Orientation during Physical Vapor Transport Growth C.H.Su, S.Feth, D.Hirschfeld, T.M.Smith, L.J.Wang, M.P.Volz, S.L.Lehoczky: Journal of Crystal Growth, 1999, 204[1-2], 41-51