Crystallization of GaN by HVPE on pressure grown seeds

Abstract

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 HVPE on the pressure grown substrates allows stable crystallization with rates of a few hundreds μm/h. The crystals with a thickness exceeding 2 mm are 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 HVPE and the heavily doped pressure grown substrates Since the critical thickness for defect generation is of the order of 100 μm, almost dislocation free layers (density below 10 4 cm -2 ) thinner than 100 μm were grown. The pressure grown substrates were then removed by mechanical polishing, or conductivity sensitive electrochemical etching (for strongly n-type substrates). Then the HVPE low dislocation density GaN platelets were used as substrates for the growth of a few mm thick bulk GaN crystals.