Deep centers and persistent photoconductivity studies in variously grown GaN films

Deep levels studies on a set of n-GaN films grown by MOCVD and HVPE reveal the presence of electron traps with levels near E-c-0.25 eV, E-c-0.55 eV, E -c-0.8 eV, E-c-1 eV, hole traps with levels near E-v+0.9 eV and a band of r elatively shallow states in the lower half of the bandgap. The total densit y of these latter states was estimated to be some 10(16) cm(-3) and they we re tentatively associated with dislocations in GaN based on their high conc entration and band-like character. None of the electron or hole traps could be unambiguously related with strong changes of diffusion lengths of minor ity carriers in various samples. It is proposed that such changes occur due to different surface recombination velocities. An important role of E-c-0. 55 eV traps in persistent photoconductivity phenomena in n-GaN has been dem onstrated.