Origins and reduction of threading dislocations in GaN epitaxial layers

We examined, using AFM and TEM, GaN nucleation layers (NLs) and early stages of high temperature (HT) GaN overgrowth on annealed NLs and HT GaN layers grown for different durations. We demonstrate that threading dislocations (TDs) do not form at the coalescence of HT GaN growths. We identify, two sources of TDs: highly defective regions in NLs and point defects present in HT GaN. We developed a novel approach for reducing TDs. We refer to it as in situ epitaxial layer overgrowth. This process entails depositing in situ a very thin silicon nitride layer on as-deposited NLs, followed by HT growth. The density of TDs is reduced to 2x 10(8) cm(-2). We ascertain the origin of the observed reduction.