Trap and non-trap dispersions in admittance spectra of hexagonal Galliumnitride

GaN-layers grown by Molecular Beam Epitaxy (MBE) on sapphire substrates were investigated using Thermal Admittance Spectroscopy (TAS). We were able to detect two electron traps with activation energies of 0.41–0.50eV and 0.63–0.67eV, respectively. Shallower emissions correlated to activation energies lower than 0.26eV were found in addition. To identify these emissions, temperature dependent conductivity measurements were analysed and similar activation energies were found assuming a thermionic emission over a barrier. We discuss these shallower emission states as inner potential barriers caused by structural inhomogeneities in the GaN layer.