The effect of the wall contact and post-growth cool-down on defects in CdTe crystals grown by 'contactless' physical vapour transport

A series of cadmium telluride crystals grown by physical vapour transport without contact with the ampoule walls and cooled at different rates were characterized using synchrotron X-ray topography, photoluminescence, and chemical etching. Strain from sticking to silica glass and its effect on the dislocation density is shown. It was found that very fast cool-down (e.g. air or water quenching) increases dislocation density by at least one order of magnitude. None of the samples had random dislocation distributions, but coarse clumping of dislocations on the scale of more than 100μm was more prevalent in slowly cooled crystals. Photoluminescence revealed that slow cooling (e.g. 10 °C/h) favoured the donor-acceptor luminescence involving complex A centres. This was diminished in fast-cooled material, an effect presumed to be due to dislocation gettering. Fast cooling also enhanced the formation of shallow acceptors. Implications for Bridgman growth of CdTe and the vapour growth of CdZnTe are discussed briefly.