Yellow luminescence and Fermi level pinning in GaN layers

A correlation between Fermi level pinning and yellow luminescence in Pt/n-GaN junctions has been studied using Schottky barrier measurements by internal photoemission spectroscopy and complementary deep level spectroscopies. The results show that illumination by photons with energies in the yellow luminescence range causes an unpinning of the interface Fermi level, accompanied by a significant increase of the Schottky barrier height from ∼1 to ∼1.9 eV. This strongly suggests the presence of acceptor states related to the yellow luminescence at the Pt/GaN interface. These states are charged in equilibrium and pin the interface Fermi level but can be optically discharged, resulting in a nearly unpinned interface.