Fermi level pinning in heavily neutron-irradiated GaN

Undoped n-GaN grown by two different metallorganic chemical vapor deposition (MOCVD) techniques, standard MOCVD and epitaxial lateral overgrowth, and Mg-doped p-GaN prepared by hydride vapor phase epitaxy and molecular beam epitaxy were irradiated with fast reactor neutrons to the high fluence of 10(18) cm(-2). In such heavily irradiated samples the Fermi level is shown to be pinned in a narrow interval of E-c-(0.8-0.95) eV, irrespective of the starting sample properties. The Fermi level pinning position correlates with the measured Schottky barrier height in n-type GaN. The results are interpreted from the standpoint of the existence of the charge neutrality level in heavily disordered material. Based on published theoretical calculations and on deep level transient spectroscopy (measurements and lattice parameter measurements in irradiated material), it is proposed that the Fermi level could be pinned between the gallium-interstitial-related deep donors near E-c-0.8 eV and nitrogen-interstitial-related acceptors near E-c-0.9 eV. (c) 2006 American Institute of Physics.