Impact of the initial stage of deposition conditions on the properties of subsequent GaN Layer

High temperature gallium nitride (HT-GaN) layers were grown by HVPE (hydride vapor phase epitaxy) method on low temperature GaN (LT-GaN) buffer layers deposited by HVPE or MOVPE method and on double MOVPE LT-GaN/AIN buffers. The (0001) sapphire substrates were applied. The HCl flow rate and deposition time intervals of nucleation layer deposition were varied in the range of 8-10 ml/min and 5-9 min (with step of 2 min) respectively. The nucleation layer was preceded by pre-heating of the substrate and followed by recrystallization process. Both processes were carried out in NH₃ ambient for 10 min. The main goal of this work was to study the influence of the initial stage of deposition process on the properties of subsequent HVPE HT-GaN layer. Morphology of LT buffer layers and HT-GaN layers were examined by scanning electron microscopy. The optical quality of thick HVPE HT-GaN layers was evaluated by the measurement of photoluminescence spectra. The X-Ray measurements (2thetas/omega, omega-002 reflection scans and reciprocal lattice maps) were performed to study the crystallographic quality of HT-GaN layers.