Improvement of electrical performance in Normally-Off GaN MOSFET with regrown AlGaN layer on the Source/Drain region

A normally-off GaN MOSFET is successfully fabricated by using the selective regrowth technique (SRT) with regrown AlGaN layer on source/drain (S/D) region. The GaN MOSFET with regrown AlGaN layer and L_g of 10 μm shows enhanced electrical performance such as maximum drain current (I_D,max) of 57 mA/mm, maximum transconductance (g_m,max) of 11 mS/mm, and field-effect mobility (μ_FE) of 59 cm²/V·s, respectively, compared to the GaN MOSFET with n⁺-GaN selective regrowth in S/D region. This is because of the high 2DEG density formed by AlGaN/GaN heterojunction in S/D region. Moreover, to accommodate the poor structural quality of the narrow region regrowth of AlGaN layer on the S/D region, wide regrown AlGaN layer is applied to the GaN MOSFET. Especially, the off-state breakdown voltage improves from 25 V to 192 V with the improved structural quality of wide regrown AlGaN layer and optimized structure and the application of the 70-nm thick SiO₂ passivation. These result shows that GaN MOSFET with wide regrown AlGaN layer on S/D region is beneficial to achieving high-quality and uniform normally-off GaN MOSFETs with excellent electrical performance.