Impact of growth pressure on defects in GaN grown by metalorganic chemical vapor deposition

Deep level optical spectroscopy and deep level transient spectroscopy have been employed to assess the effect of growth pressure on bandgap states of GaN grown by metalorganic chemical vapor deposition. Samples were grown at 760 and 76 torr and their defect spectra and electrical properties were compared. The sample grown at atmospheric pressure was unintentionally doped with a light n-type background. Samples grown at low-pressure incorporate excess carbon, which renders highly resistive GaN in the absence of co-doping, while the silicon co-doped sample proves to be n-type but heavily compensated. The acceptor-like deep level near E_c - 2.6 eV is greatly affected by the reduced pressure growth per se, exhibiting a shift in activation energy as well as a large increase in concentration. Donor trap states observed closer to the conduction band show little dependence on the growth pressure and occur with very low concentration. The physical origins of these levels are discussed.