The deep-level energy distribution which was associated with the well-known yellow luminescence was studied by using 2 complementary deep level techniques: photoluminescence and surface photo-voltage spectroscopy. The results showed that the yellow luminescence was due to the capture of conduction-band electrons, or electrons from shallow donors (with a maximum depth of the order of the thermal energy) by a deep acceptor level with a broad energy distribution centered at about 2.2eV below the conduction-band edge. The results also showed that the density of yellow luminescence-related states had a significant surface component.

Yellow luminescence and related deep levels in unintentionally doped GaN films I.Shalish, L.Kronik, G.Segal, Y.Rosenwaks, Y.Shapira, U.Tisch, J.Salzman: Physical Review B, 1999, 59[15], 9748-51