Detection of dislocation-related midgap levels in pulsed laser deposited GaN by photo-induced current transient spectroscopy

Deep levels in unintentionally doped GaN epilayers grown on sapphire (0001) by ultra high vacuum pulsed laser deposition at 600 and 700 degrees C have been studied using photo-induced current transient spectroscopy (PICTS). The GaN epitaxial layers were deposited by laser ablating a hydride vapor phase epitaxy grown bulk GaN polycrystalline target in the ambient of r.f. nitrogen radicals. The activation energy of dark conductivity for these layers lies in the range 0.17-0.25 eV. An acceptor-like deep trap level is detected in the PICTS spectrum with activation energy of 1.32 eV. For the 700 degrees C grown GaN layer, an additional well-pronounced acceptor-like defect level near mid-gap at 1.52 eV has been observed. From the analysis of trap capture kinetics, both defect levels are identified to be extended 'bandlike' electronic states associated with extended defects such as dislocations present in GaN layers. (C) 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim