PRECIPITATES IN GAN EPILAYERS GROWN ON SAPPHIRE SUBSTRATES

Precipitates in GaN epilayers grown on sapphire substrates were invest igated by atomic number contrast (ANC), wavelength-dispersive x-ray sp ectrometry (WDS), energy-dispersive spectrometry (EDS), and cathodolum inescence (CL) techniques. The results showed that the precipitates ar e mainly composed of gallium and oxygen elements and distribute more s parsely and inhomogeneously in [11 (2) over bar 0] directions in the s ample grown on substrate nitridated for a longer period. Yellow lumine scence intensity was imaged to be stronger in the precipitates. The re sults suggest that the precipitates are formed on dislocations and gra in boundaries by substituting oxygen onto the nitrogen site, and resul t in the formations of deep levels nearby.