Raman scattering from defects in GaN: The question of vibrational or electronic scattering mechanism

We present a comprehensive Raman study on defects in GaN, which appear in t he Raman spectra as sharp and intense lines in the low-energy region from 9 5 to 250 cm(-1). These lines decrease nearly exponentially in intensity wit h increasing temperature and are excitable only in the range 2.0-2.5 eV. Th eir temperature behavior seems to be incompatible with vibronic excitations but indicates an electronic-scattering mechanism. However, our magnetic-fi eld- and high-pressure-dependent Raman measurements contradict this interpr etation. We show in contrast that all lines are caused by vibrational Raman scattering in which the temperature dependence is due to the resonance pro cess. We demonstrate in a doping study that the responsible defects are rel ated to As impurities incorporated into the GaN material. [S0163-1829(98)00 344-0].