Photo-etching of HVPE-grown GaN: Revealing extended non-homogeneities induced by periodic carrier gas exchange

The influence of periodic changes of carrier gas composition (H2 and N2+10%H2) on structural and physical properties of GaN crystals grown by Hydride Vapor Phase Epitaxy (HVPE) was studied using photo-etching, defect-selective etching (DSE), secondary ions mass spectroscopy (SIMS), low temperature photo-luminescence (LTPL) and Raman spectroscopy. The studies were performed on (1-100) cleavage planes of thick crystals grown with short (a few minutes) and long (one hour) periods of the carrier gas exchange. Markedly large differences between the level of impurities (Si, C, O2, H2) were measured by SIMS in the GaN grown in [0001] direction and inside the V-shape defects, that well correlates with corresponding different carrier concentration levels revealed by Raman and photo-etching. Small differences in carrier concentration across the striations in the [0001] direction were clearly revealed by photo-etching, while PL and Raman appeared to be not sensitive to them.