Normally off behavior of high Al composition AlGaN channel HEMT with p-NiO gate dielectric and barrier recess

High aluminum (Al) composition AlGaN has emerged as a promising material for next generation power semiconductor devices. In this work, we have demonstrated a normally off Al0.84Ga0.16N/Al0.65Ga0.35N high electron mobility transistor (HEMT) with threshold voltage (Vth) ranging from −0.07 to 1.30 V by utilizing radio frequency magnetron sputtered p-type NiO and barrier recess in the gate region. The maximum breakdown voltage of these devices was measured to be 1770 V, corresponding to an average breakdown field of ∼1.26 MV/cm. The device exhibited a maximum drain current of 27.4 mA/mm at a gate-to-source voltage (Vgs) of 2.5 V and a drain-to source voltage (Vds) of 10 V. The sputtering condition of p-NiO with various Ar:O2 ratios was characterized using x-ray photoelectron spectroscopy and the transfer length method. Under Ar:O2 = 3:4, p-NiO showed the lowest Rsheet as well as the highest Ni3+/Ni2+ ratio and was adopted for normally off device fabrication. The contributions of the p-NiO and barrier recess in the positive shift of the threshold voltage (Vth) were decoupled by fabricating HEMTs with different p-NiO and barrier recess combinations. With +0.93 to +1.77 V contributed to p-NiO, and +7.09 to +7.33 V contributed to the barrier recess in the gate region. This result provides a low thermal budget alternative to realize normally off AlGaN channel HEMTs.