Physical vapor transport growth of large AlN crystals

Single crystals of aluminum nitride were grown by physical vapor transport (PVT) method. Evaluation of transport conditions was carried out during bulk growth of aluminum nitride in a vertical, cylindrical geometry. Experiments were carried out for the conditions in which we varied thermal gradients ( T H– T C=30–90° C). Crystals grown at low thermal gradients and lower source temperature (below 2100°C) showed dominantly needle morphology. As we increased the source temperature hexagonal morphology became dominant. We achieved sizes up to 25 mm diameter and fabricated these crystals into wafers. The purity and quality of needle and large (25 mm diameter) crystal were evaluated by microprobe studies and x-rocking curve. The needle crystals showed very good quality and did not show small angle boundaries compared to large crystal in which we observed many small angle boundaries. There was no effect of N 2 background pressure of 200–500 Torr range on the morphology of the crystal. The crystal showed FWHM of 0.08° and lattice parameters were very much in agreement with the literature value of AlN.