Simulation study on electrical characteristic of AlGaN/GaN high electron mobility transistors with AlN spacer layer

Abstract

Two-dimensional electron gas (2DEG) property is crucial for the performance of GaN-based high electron mobility transistors (HEMTs). The 2DEG-related concentration and mobility can be improved as device’s performance booster. Electrical characteristics of AlGaN/AlN/GaN HEMT are numerically simulated and compared with conventional AlGaN/GaN HEMT. The main findings of this study indicate that 2DEG’s concentration level is increased when a spacer layer of AlN in the interface of AlGaN/AlN/GaN is inserted owing to large conduction band off set, high polarization field, and high barrier. Notably, when a thin spacer layer of AlN is introduced, the 2DEG’s distribution virtually shifts away from the interface which reduces the interface scattering. The scattering appearing in conventional AlGaN/GaN HEMT includes alloy and interface roughness scatterings. They are reduced in AlGaN/AlN/GaN HEMT due to binary nature of AlN material. A critical thickness of spacer layer for mobility is 0.5 nm and the maximum drain current and transconductance ( G m ) are at 1.5 and 1.2 nm thickness of AlN spacer layer. Increasing thickness of AlN spacer layer deteriorates the ohmic resistance of source/drain contact and hence degrades the performance of device beyond 1.5-nm-thick AlN spacer layer.