High-voltage MIS-gated GaN transistors

Transistors with a high electron mobility based on AlGaN/GaN epitaxial heterostructures are promising component types for creating high-power electronic devices of the next generation. This is due both to a high charge-carrier mobility in the transistor channel and a high electric durability of the material making it possible to achieve high breakdown voltages. For use in power switching devices, normally off GaN transistors operating in the enrichment mode are required. To create normally off GaN transistors, the subgate region on the basis of $p$-GaN doped with magnesium is more often used. However, optimization of the $p$-GaN epitaxial-layer thickness and doping level makes it possible to achieve a threshold voltage close to $V_{\operatorname{th}}$ = +2 V for the on-mode of GaN transistors. In this study, it is shown that the use of a subgate MIS (metal–insulator–semiconductor) structure involved in $p$-GaN transistors results in an increase in the threshold voltage for the on-mode to $V_{\operatorname{th}}$ = +6.8 V, which depends on the subgate-insulator thickness in a wide range. In addition, it is established that the use of the MIS structure results in a decrease in the initial transistor current and the gate current in the on mode, which enables us to decrease the energy losses when controlling powerful GaN transistors.