Enhancement-mode AlGaN/GaN HFET with buried-junction-barrier for breakdown improvement and threshold-voltage modulation

Abstract

A novel AlGaN/GaN heterojunction field-effect transistor (HFET) with buried-junction-barrier (BJB) is proposed in this work. In the BJB-HFET, a thin PGaN layer was inserted in the unintentionally doped GaN channel layer, which introduces a buried PN-junction beneath the gate region. Owing to the presence of the PN-junction, in “OFF-state”, a reverse-biased barrier for electrons is formed along the channel in GaN buffer, which effectively reduces the buffer leakage current of the device. Moreover, the BJB also facilitates to obtain a uniform electric-field (E-field) distribution in the depletion region that dictates breakdown voltage (BV) improvement. For a AlGaN/GaN BJB-HFET with a gate-drain distance of 5 μm, a BV as high as 1190 V at leakage current of 10 μA/mm is achieved with a low specific on-resistance (Ron,sp) of 0.54 mΩ cm2, which yields a significantly high Baliga's Figure-of-Merit (FOM) of 2.83 GW/cm2. Besides, benefiting from the energy-band modulation capability of the BJB structure, a higher threshold-voltage (Vth) can be simultaneously obtained in the BJB-HFET compared with the conventional heterojunction field-effect transistor (Conv. HFET). The proposed BJB structure is of great potential for high performance AlGaN/GaN power transistors.