Residual impurities in GaN substrates and epitaxial layers grown by various techniques

Low-temperature/high-resolution photoluminescence spectra of thick freestanding hydride vapor-phase epitaxial GaN substrates show intense sharp lines in the near bandedge spectral region, which has been previously assigned to recombination processes associated with the annihilation of excitons bound to neutral Si and O donors. Similar studies carried out on unintentionally doped (UID) and Si-doped homoepitaxial films grown by molecular beam epitaxy and metalorganic chemical vapor deposition methods, respectively, supports the previous identification of Si and O as the dominant shallow donors in UID GaN. The chemical nature of these background impurities and dopants were verified by high sensitivity secondary ion mass spectroscopy. The present work confirms Si and O as the pervasive dominant shallow donors in UID GaN and demonstrate the usefulness of photoluminescence as a non-destructive technique to identify impurities in GaN.