Polarization-Engineered n+GaN/InGaN/AlGaN/GaN Normally-Off MOS HEMTs

The proposal, processing and performance of n(+)GaN/InGaN/AlGaN/GaN normally-off metal-oxide-semiconductor (MOS) HEMTs with a recessed 2-mu m long gate/8-mu m source-drain distance are presented. It is shown that by using a negative polarization charge at the InGaN/AlGaN interface together with 10-nm thick Al2O3 gate insulation, a threshold voltage V-T increases by 3.6V reaching a value of similar to 1.6V. Moreover, the combination of the gate recessing through the n(+)GaN cap and gate insulation lead to an invariant maximal drain current of about 0.25Amm(-1), as well as decreased gate leakage current in the order of similar to 10(-9)Amm(-1). Analytical equations explain the predictive setting of V-T up to 7V with the oxide thickness t(ox) increase, if holes compensate the negative polarization charge. By applying t(ox)=30nm a V-T similar to 3V was obtained; p-doping of the cap/barrier layers is suggested to reach the theoretically predicted scalability.