Fermi-level stabilization energy in group III nitrides

Energetic particle irradiation is used to systematically introduce point defects into In1-xGaxN alloys over the entire composition range. Three types of energetic particles (electrons, protons, and He-4(+)) are used to produce a displacement damage dose spanning five decades. In InN and In-rich InGaN the free electron concentration increases with increasing irradiation dose but saturates at a sufficiently high dose. The saturation is due to Fermi level pinning at the Fermi stabilization energy (E-FS), which is located at 4.9 eV below the vacuum level. Electrochemical capacitance-voltage (ECV) measurements show that the pinning of the surface Fermi energy at E-FS is also responsible for the surface electron accumulation in as-grown InN and In-rich InGaN alloys. The results are in agreement with the amphoteric defect model that predicts that the same type of native defects are responsible for the Fermi level pinning in both cases.