Identification of deep levels in GaN associated with dislocations

Abstract

To establish a correlation between dislocations and deep levels in GaN, a deep-level transient spectroscopy study has been carried out on GaN samples grown by metalorganic chemical vapour deposition. In addition to typical undoped and Si-doped GaN samples, high-quality crack-free undoped GaN film grown intentionally on heavily doped cracked Si-doped GaN and cracked AlGaN templates are also chosen for this study. The purpose of growth of such continuous GaN layers on top of the cracked templates is to reduce the screw dislocation density by an order of magnitude. Deep levels in these layers have been characterized and compared with emphasis on their thermal stabilities and capture kinetics. Three electron traps at Ec–ET∼0.10–0.11, 0.24–0.27 and 0.59–0.63 eV are detected common to all the samples while additional levels at Ec–ET∼0.18 and 0.37–0.40 eV are also observed in the Si-doped GaN. The trap levels exhibit considerably different stabilities under rapid thermal annealing. Based on the observations, the trap levels at Ec–ET∼0.18 and 0.24–0.27 eV can be associated with screw dislocations, whereas the level at Ec–ET∼0.59–0.63 eV can be associated with edge dislocations. This is also in agreement with the transmission electron microscopy measurements conducted on the GaN samples.