High performance enhancement-mode HEMT with 3DEG to conduct current and 3DHG as back barrier

Abstract

Abstract A novel enhancement-mode (E-mode) high electron mobility transistor (HEMT) with three-dimensional electron gas (3DEG) and three-dimensional hole gas (3DHG) is presented. It features a GaN-top layer, a positive graded AlGaN barrier layer (GAL), and a negative graded AlGaN back barrier layer (GABL) (wherein the positive/negative doping gradient is defined with respect to the growth direction), with a vertical conduction channel aside a MIS trench gate. The 2DHG is formed at the interface between the GaN-top layer and GAL. The 3DEG and 3DHG are formed due to the polarization induced by linearly grading Aluminum (Al) composition from 0 to xAl in GAL and 0.4 to 0 in GABL, respectively. The source and drain locate at the same side of the MIS trench gate, and the source contacts with the gate. Firstly, 2DHG blocks the electron current conduction path between the source and 3DEG so as to achieve E-mode. Secondly, the high-sheet density 3DEG in GAL greatly increases the on-state current. Thirdly, the leakage current effectively is reduced by the 3DHG in GABL, improving the breakdown voltage. Fourthly, a high breakdown voltage (BV) is obtained because the polarization junction formed by the polarization charges in GAL and GABL improves the electric field distribution in the drift region. The BV of the proposed HEMT increases to 1080 V from 47 V of the conventional MIS HEMT at the same length of the drift region, and specific on-resistance (Ron,sp) decreases to 0.29 mΩ cm2 from 0.64 mΩ cm2 in simulation.