Laboratory HAXPES of GaN structures for power electronic

Abstract : High-electron-mobility transistors (HEMTs) based on AlGaN/GaN heterostructures are being developed for high power electronic. The presence of a two-dimensional electron gas (2DEG) at the AlGaN/GaN interface enables reaching high electron mobility (>1500 cm$^2$.V-1.s-1). For safety and reliability reasons, normally-off HEMTs are requested and can be obtained by the full recess approach, based on the removal of the AlGaN layer underneath the gate. The dielectric (Al$_2$O$_3$) and metal gate are directly deposited on the etched GaN surface to create a metal-insulator-semiconductor (MIS) structure, giving rise to the so-called MIS-HEMTs. The final devices properties strongly depend on the quality of the buried Al$_2$O$_3$/GaN interface. Advanced chemical characterization of this critical interface is thus mandatory. Laboratory HAXPES has recently appeared and its use is quickly rising for optimizing technological devices [3]. It is here a promising technique to investigate a more realistic Al$_2$O$_3$/GaN interface, e. g. with a thick Al$_2$O$_3$ layer. We have developed specific protocols to investigate the impact of Al$_2$O$_3$ thickness, precursors and post-deposition anneal on the GaN surface oxidation and stoichiometry.