Shallow donors in GaN studied by electronic Raman scattering in resonance with yellow luminescence transitions

Electronic excitations in nominally undoped GaN have been investigated by Raman scattering. Peaks in the range between 18.5 and 30 meV have been assigned to internal shallow donor transitions in cubic and hexagonal GaN, respectively. The photon energy dependence of the scattering efficiencies in the cubic phase is explained by Raman scattering in resonance with the so-called ‘‘yellow’’ luminescence transitions. This interpretation supports models for the notorious yellow luminescence in which shallow donors are involved. These shallow donors most likely do not originate from native point defects.