Growth of AlN and GaN Bulk Crystals from the Vapor Phase

Abstract

Abstract : Prolonged growth of GaN single crystals resulted in decomposed crystals at high ammonia pressures (>430 Torr). Gas composition analysis using quadrupole mass spectrometry revealed that hydrogen concentration in the gas phase increased with increasing ammonia total pressure above 475 Torr in the absence of Ga source and at above 300 Torr in the presence of Ga source. The enhanced decomposition of GaN at higher pressures can be attributed to the role of H2 in etching of GaN. Decomposition of GaN in the current study may be attributed to thermodynamic instability and evaporation at low total pressures and decomposition due to hydrogen etching as a result of the decomposition of ammonia at high total pressures. Nitrogen dilution of ammonia reduced the amount of hydrogen generated as a result of ammonia decomposition and alleviated decomposition of GaN crystals. A 2 mm x 1.5 mm GaN crystal was grown with minimal decomposition via seeded growth in a 40 sccm NH3 and 20 sccm N2 gas mixture.