Vertical design of cubic GaN-based high electron mobility transistors

Abstract

Cubic (zinc blende) AlGaN/GaN heterostructures for application in GaN-based high electron mobility transistors are investigated theoretically. The formation of 2DEGs (two-dimensional electron gas) in cubic AlGaN/GaN structures is studied, carrier distributions and threshold voltages are calculated, and design issues are investigated. For the calculations, a Schrödinger-Poisson solver and a simple analytical model developed in the present work are used. It is shown that due to the barrier doping needed for the formation of a pronounced 2DEG in cubic structures, undesirable saturation effects of the 2DEG density may occur. Options to avoid 2DEG saturation and to realize cubic normally-off HEMTs are elaborated. The behavior of cubic AlGaN/GaN structures is compared to that of their hexagonal counterparts.