Vibrational modes were observed at 544/cm, in O-doped material under ambient pressures, by using Raman spectroscopy. An investigation of these modes, under an applied hydrostatic pressure, revealed the existence of 3 closely spaced modes that shifted in relative intensity with increasing pressure. In particular, transitions between the various modes occurred at previously observed electronic transitions that were associated with the DX-like center behavior of substitutional O on N sites. A simple 1-dimensional oscillator model was used to deduce approximate force constants. These were consistent with the attribution of the 544/cm mode to ON, and with the force constants for C and B dopants in GaP. The relative intensity changes which were observed at 11 and 17GPa were associated with changes in the charge state, due to the merging of +/0 ionization level and the Fermi energy and with the transition to DX that caused the previously observed drop in free electron concentration, respectively.

Localized Vibrational Modes in GaN:O Tracing the Formation of Oxygen DX-Like Centers under Hydrostatic Pressure C.Wetzel, H.Amano, I.Akasaki, J.W.Ager, I.Grzegory, M.Topf, B.K.Meyer: Physical Review B, 2000, 61[12], 8202-6