Self-Aligned Technology for N-Polar GaN/Al(Ga)N MIS-HEMTs

In this letter, we introduce a scalable self-aligned technology for N-polar GaN MIS-HEMTs which can be used to achieve significant improvement in device performance by minimizing the source and drain access resistances. The methodology consists of a refractory-metal gate-first process followed by the regrowth of polarization-doped graded InGaN and InN layers by plasma-assisted molecular-beam epitaxy. The regrowth has been optimized to achieve ohmic contact resistance as low as 23 Ω-μm to the N-face 2-D electron gas. Excellent maximum current of 1.4 A/mm and a very low on resistance of 590 Ω-μm was achieved at (V_G - V_T) = 6 V for L_G = 500 nm. Peak transconductance of 343 mS/mm is also state of the art for the given gate length and aspect ratio. Excellent f_T.L_G product of 15.9 GHz-μm with minimal drain delay was also achieved for L_G = 600 nm.