Structural analysis of thick GaN films grown by hydride vapour phase epitaxy

Thick GaN films were deposited on sapphire substrate by hydride vapour phase epitaxy (HVPE) in two steps at 1050 °C. The substrate was first nitridated for different times between 1 and 10 minutes before deposition of a 12 pm thick layer. X-ray rocking curves show a minimum for 5 and 7 minutes of nitridation. The shift of the photoluminescence peak (PL) at room temperature from 3.328 to 3.405 eV is consistent with the evolution of the microstructure which is characterised by non-compact layers for the shortest times of nitridation. The nitridation of the sapphire surface results in the formation of a damaged layer with a thickness varying with the nitridation times. In this interfacial area, flat interfaces are present, but A1N nanocrystals may be observed as well as an amorphous zones containing Al, O and N.