The role of deep levels in the persistent photoconductivity in Mg-doped GaN grown by MOCVD

Electrical properties of Mg doped GaN epilayers grown by metalorganic chemi cal vapor deposition were investigated using photocapacitance measurements. Annealing at different temperatures gave gradual activation of Mg-acceptor s in samples taken from the same as-grown wafer. The samples exhibit a clea r persistent photocapacitance at low temperatures. Measurements of the phot ocapacitance as a function of excitation energy show the presence of energy levels at 1.1 and 1.9 eV from the valence band. The concentration of both traps increases with the temperature and duration of the annealing. We show that the traps are metastable and conclude that they are related to the Mg doping. Our results support the hypothesis that the PPC observed in GaN:Mg originates from these metastable deep Mg-related centers. (C) 1999 Elsevie r Science B.V. All rights reserved.