The effect of AlN nucleation growth conditions on the inversion channel formation at the AlN/silicon interface

In recent years, GaN grown on silicon substrates (GaN-on-Si) managed to offer a commercial solution for harvesting the advantages of GaN-based devices whilst benefiting from the well-established silicon-based infrastructure. Although having an upper hand when it comes to cost, GaN-on-Si suffers from a vertical breakdown voltage which was found to be limited by the silicon substrate [1]. Earlier investigations showed that this breakdown is related to the formation of an inversion channel at the interface between the nucleation layer and the silicon substrate [2, 3]. This inversion layer acts as a source for electron injection during the application of high positive voltages relative to the substrate, thus leading to a premature breakdown. In this work we report on the characterization of this inversion channel and demonstrate that it can be suppressed by optimizing the growth conditions of the AlN nucleation layer. To obtain a deeper understanding of the inversion layer properties, two MOCVD AlN nucleation samples were grown on highly p-doped Silicon substrates, growth temperatures between 800 °C and 950 °C, while the desorption temperature was held at 950 °C. Vertical structures were then etched, with annealed Ti/Al/Ni/Au as ohmic contact to the silicon and Ni/Au Schottky contact to the AlN.