Simulation of a high-performance enhancement-mode HFET with back-to-back graded AlGaN layers
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A novel three-dimensional hole gas (3DHG) enhancement-mode (E-mode) heterostructure fieldeffect transistor (HFET) is proposed and investigated. It features back-to-back graded AlGaN (BGA) barrier layers consisting of a positive-graded AlGaN layer and a negative-graded AlGaN layer, which form polarization gradient and subsequently induce the three-dimensional electron gas (3DEG) and 3DHG in the positiveand negative-graded AlGaN layers, respectively. The source and drain are located at the same side of the metal-insulator-semiconductor (MIS) trench gate, and the source is in contact with the HfO2 gate insulator. First, the on-state current is significantly improved owing to the high-density 3DEG in the positive-graded AlGaN. Next, the vertical conductive channel between the source and 3DEG is blocked by the 3DHG, thereby realizing the E-mode. The threshold voltage (Vth) can be modulated by a partial doping conductive channel. Subsequently, a high breakdown voltage (BV) is obtained, because the polarization junction formed by the polarization charges assists in depleting the drift region in the off-state. Next, the BGA-HFET is smaller than the conventional HFET (Con-HFET) owing to the special location of the source. The BV of the proposed HFET sharply increases to 919 V from 39 V of the Con-HFET with the same gate-drain spacing, and the saturation drain current is increased by 103.5%.
Keywordsgraded AlGaN 3DHG-3DEG large on-state current high voltage enhancement mode
This work was supported in part by National Natural Science Foundation of China (Grant Nos. 51677021, 61234006), National Defense Science and Technology Project Foundation of China (Grant No. 1100395), and Fundamental Research Funds for the Central Universities (Grant No. ZYGX2014Z006).
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