Modeling the Effect of the Two-Dimensional Hole Gas in a GaN/AlGaN/GaN Heterostructure

GaN/AlGaN/GaN based normally-off high electron mobility transistors (HEMTs) are promising candidates for future high-power as well as high-frequency applications. Here, a physics-based analytical model is presented to explain the effect of a thick GaN cap layer on the two-dimensional electron gas (2DEG) density at the AlGaN/GaN interface, and the surface barrier height in a AlGaN/GaN heterostructure. It has been considered that the surface donor states on the GaN cap top donate electrons to form the 2DEG. Moreover, the impact of a 2D hole gas, formed when the valence band crosses the Fermi energy level, has been scrutinized. This model provides a tool for designing such a GaN/AlGaN/GaN based device over a wide parameter range. The model is shown to match well with available experimental data.