Positive Threshold Voltage Shift in AlGaN/GaN HEMTs and E-Mode Operation By ${\mathrm{Al}}_{x}{\mathrm{Ti}}_{1-x}$ O Based Gate Stack Engineering

In this paper, for the first time, we have experimentally demonstrated enhancement mode (e-mode) AlGaN/GaN high-electron-mobility transistor (HEMT) operation by integrating p-type high-κ Al_xTi_1-xO based gate stack. Concentration of Al in Al-Ti-O system was found to be a tuning parameter for the threshold voltage of GaN HEMTs. The high-κ properties of Al_xTi_1-xO as a function of Al % are studied. Superiority of AlTiO over other p-oxides such as CuO and NiO_x is proven statistically. Using the high-κ and p-type AlTiO, in conjunction with a thinner AlGaN barrier under gate, 600-V e-mode GaN HEMTs are demonstrated with superior ON-state performance (I_ON ~ 400 mA/mm and R_ON = 8.9 Q-mm) and gate control over channel (I_ON/I_OFF = 10⁷, SS = 73 mV/dec, and gate leakage <; 200 nA/mm), beside improved safe operating area reliability.