Sulfur Incorporation at Interface Between Atomic-Layer-Deposited Al2O3 Thin Film and AlGaN/GaN Heterostructure

Abstract

Surface incorporation at the interface between atomic-layer-deposited Al2O3 thin film and AlGaN/GaN heterostructure was studied based on the understanding of charge configuration and electronic band structure through fabrication and numerical simulation. The annealing in H2S ambient at various temperatures prior to deposition of Al2O3 gate insulator incorporated the sulfur. The Al2O3 was formed on the sulfur treated GaN cap/AlGaN barrier/GaN by trimethylaluminum and water-based atomic layer deposition. Thereafter, TiN electrode was sputtered on the Al2O3, which was followed by forming gas annealing. The time-of-flight secondary ion mass spectroscopy disclosed that the sulfur located at the interface of Al2O3/GaN cap, of which concentration increased with annealing temperature. Positive charges at the interface of Al2O3/GaN cap induced by sulfur increased the two-dimensional electron gas density and shifted the pinch-off voltage in the negative direction. The diffusion of sulfur in the GaN cap and AlGaN barrier can hamper the electron accumulation under positive gate voltage and shifts the accumulation voltage of the spillover region in the positive direction. Furthermore, the incorporated sulfur suppressed the gate leakage current.