Theoretical investigations on the N-polar GaN/AlxGa1-xN/GaN heterostructures: Considering the existence of both two-dimensional hole and electron gases

Abstract

In this paper, a theoretical study of N-polar GaN/AlxGa1-xN/GaN heterostructures is conducted systematically. The dependence of two-dimensional hole gas (2DHG, at the bottom AlxGa1-xN/GaN interface) and electron gas (2DEG, at the upper GaN/AlxGa1-xN interface) sheet densities on variables, such as GaN top layer thickness, AlxGa1-xN back barrier thickness, and Al content, is investigated. The effect of n-type doping in AlxGa1-xN and δ-doping concentrations in the GaN buffer on 2DHG and 2DEG sheet densities is also presented. For the unintentionally doped structure, the 2DHG-induced electric field E2DHG provides the only driving force in the 2DEG formation. Thus, in order to get high dense of 2DEG in such heterostructure, 2DEG and 2DHG shall coexist through proper AlxGa1-xN back barrier design. While for intentionally doped structure (with the n-type doped AlxGa1-xN back barrier layer or δ-doped GaN buffer layer), ionized donor-induced electric field Edonor is another driving force for 2DEG. The obtained insight offers indications for the structure design of the N-polar GaN/AlxGa1-xN/GaN high electron mobility transistors.