Positive Threshold Voltage Shift in AlGaN/GaN HEMTs and E-Mode Operation By $${$$\backslash$mathrm ${$Al$}$$}$ _ ${$x$}$${$$\backslash$mathrm ${$Ti$}$$}$ _ ${$1-x$}$ $ 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 _x Ti _1-x O 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 _x Ti _1-x O 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 = 10 ⁷ , SS = 73 mV/dec, and gate leakage <; 200 nA/mm), beside improved safe operating area reliability.