Two-dimensional electron and hole gases in InxGa1− xN/AlyGa1− yN/GaN heterostructure for enhancement mode operation

In this paper, a numerical study of InxGa1−xN/AlyGa1−yN/GaN heterostructure is presented. The dependence of two-dimensional electron gas (2DEG) and two-dimensional hole gas (2DHG) sheet densities on variables, such as InxGa1−xN layer thickness and In content, and AlyGa1−yN barrier layer thickness and Al content, are systematically investigated. The effect of P-type doping in InxGa1−xN on 2DEG and 2DHG sheet densities in this heterostructure is also studied. It is shown that the strong reverse electric field in InxGa1−xN cap layer contributes to the depletion of 2DEG at the AlyGa1-yN/GaN interface. When InxGa1−xN layer thickness and In content increases, 2DEG sheet density decreases significantly. P-type doping shows less influence on 2DEG compared to the polarization electric field in InxGa1−xN layer. In addition, there exist critical values for all the variables beyond which 2DHG appears at the interface of InxGa1−xN/AlyGa1−yN. Once 2DHG appears, it will prevent 2DEG from being further depleted. With proper design of AlyGa1−yN layer, the coexistence of 2DEG and 2DHG in InxGa1−xN/AlyGa1−yN/GaN structure can be avoided, showing that this structure has great potential in the fabrication of enhancement mode (E-mode) high electron mobility transistors.