Effects of pre-deposition annealing prior to gate insulator deposition in planar AlGaN/GaN MIS-HEMT with a thin AlGaN barrier layer

Abstract

A planar-type enhancement-mode transistor, termed an extrinsically electron induced by a dielectric (EID) AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistor (HEMT), is a promising candidate for reliable and stable high-power switching devices, since it can be fabricated without damaging processes such as dry etching, fluorine plasma exposure, or Mg doping. This study revealed that the AlGaN surface annealing process prior to gate insulator deposition contributes to enhancing the threshold voltage (Vth) in the EID AlGaN/GaN HEMTs. Consequently, a high Vth of 4.6 V was achieved with a large figure of merit of 280 MW/cm2. The enhancement of Vth is attributed to an increased density of interfacial states and the resulting suppression of channel mobility caused by the surface annealing. It was also confirmed that the interface states do not adversely affect the stability of the transfer characteristics but, conversely, improve it.