Analytical models of the transition layer in HEMTs on silicon substrate for device simulation

One way to increase the breakdown voltage in heterojunction field-effect-transistors (HFETs) on silicon substrate is to introduce a transition (buffer) layer made of a sandwich of thin AlN/AlGaN layers between the silicon substrate and the GaN well. The effect of this transition layer is to average out and, in this way, to reduce the local mechanical stress that appears between the silicon substrate and the GaN layer because of the different lattice constants of the two layers. In this article we present an analytical model for the simulation of the transition layer in AlN/AlGaN transistors. The model is based on writing explicitly the interface conditions at each boundary and solving the resulting system of equations analytically. The final equation is written in the form of a standard mixed-type boundary condition that can be relatively easy implemented in device simulators.