The effect of interface polarity on the basal dislocations at the GaN/AlN interface.

The unavoidable high-density dislocations in GaN usually hinder the normal operation of GaN-based devices. The current theoretical research studies mainly focus on threading dislocations in the bulk GaN crystal. Here, we alternatively turn our attention to the basal dislocations, which have been directly observed in experiments but have been less studied. The results from the density-functional theory and empirical molecular dynamic calculations indicate that the Al-polar GaN/AlN interface is more conductive to the formation of Shockley partial dislocations, which are the main dislocations formed during the early growth of GaN on AlN and the precursor of the threading edge dislocations. The dislocation density and local geometry in GaN deposited on AlN strongly depend on the temperature. Overall, choosing N-polar AlN as a substrate for GaN growth at 1900 K helps to obtain high-quality GaN with a greater wurtzite structure content and fewer dislocations.