Growth of GaN under pressure from solution in gallium results in almost dislocation free plate-like crystals but with size limited to approx. 1 cm (lateral) and 100 µm (thickness). On the other hand, deposition of GaN by hydride vapour-phase epitaxy on the pressure grown substrates allows stable crystallization with rates of a few hundreds µm/h. The crystals with a thickness exceeding 2mm were grown in this way. However, in these thick GaN crystals grown directly on almost dislocation free substrates quite high number of dislocations appears if the crystal thickness exceeds certain critical value probably due to a small lattice mismatch between GaN grown by hydride vapour-phase epitaxy and the heavily doped pressure grown substrates Since the critical thickness for defect generation was of the order of 100µm, almost dislocation free layers (density below 104/cm2) thinner than 100µm were grown. The pressure grown substrates were then removed by mechanical polishing, or conductivity sensitive electrochemical etching (for strongly n-type substrates). Then the hydride vapour-phase epitaxy low dislocation density GaN platelets were used as substrates for the growth of a few mm thick bulk GaN crystals.

Crystallization of GaN by HVPE on Pressure Grown Seeds. I.Grzegory, B.Lucznik, M.Bockowski, B.Pastuszka, G.Kamler, G.Nowak, M.Krysko, S.Krukowski, S.Porowski: Physica Status Solidi A, 2006, 203[7], 1654-7