A series of crystals, grown by physical vapor transport without contact with the ampoule walls and cooled at various rates, were characterized by using synchrotron X-ray topography, photoluminescence and chemical etching. Strains which arose from sticking to silica glass, and their effect upon the dislocation density, were studied. It was found that very fast cooling (air- or water-quenching) increased the dislocation density by at least an order of magnitude. None of the samples had random dislocation distributions, but coarse clumping of the dislocations at a scale of more than 100μm was more prevalent in slowly-cooled crystals. The photoluminescence revealed that slow cooling (10C/h) favored a donor–acceptor luminescence which involved complex A-centers. This was decreased in quickly-cooled material, and this was presumed to be due to dislocation gettering. Rapid cooling also enhanced the formation of shallow acceptors.

The Effect of the Wall Contact and Post-Growth Cool-Down on Defects in CdTe Crystals Grown by ‘Contact-Less’ Physical Vapour Transport. W.Palosz, K.Grasza, K.Durose, D.P.Halliday, N.M.Boyall, M.Dudley, B.Raghothamachar, L.Cai: Journal of Crystal Growth, 2003, 254[3-4], 316-28