Threshold Voltage Stability Enhancing Technology for p-GaN HEMTs Using Hybrid Gate Structure

A novel hybrid gate p-GaN power high-electron mobility transistor (Hyb-HEMT) technology is proposed in this work to effectively enhance threshold voltage ( V _th ) stability without significant gate leakage current ( I _gss ) degradation. In this device concept, gate structure consists of spaced ohmic-type p-GaN metal dots and Schottky-type p-GaN metal. Charge storage effect can be alleviated through a free-carrier “discharge path” induced by ohmic-type p-GaN region, thus enhancing the Vth stability. The surrounding geometry distribution of Schottky-type p-GaN metal can take full advantage of depletion region, ensuring a relatively low I _gss . It is experimentally demonstrated that hybrid gate structure can successfully suppress V _th shift within only 0.03V under 1200s DC drain/gate bias stress and the activation energy ( E _A ) of proposed Hyb-HEMT is only 0.59eV, which indicates Hyb-HEMT owns shallower traps, leading to easier discharge of the induced stored charges. Meanwhile, experimental results and the mix-mode simulation prove that no carrier injection or trapping effect occurs in p-GaN layer after repetitive reverse freewheeling stress for the Hyb-HEMT device.