High fmax with High Breakdown Voltage in AlGaN/GaN MIS-HFETs using In-Situ SiN as Gate Insulators

AlGaN/GaN heterojunction transistors (HFETs) with metal-insulator-semiconductor (MlS)-type gate structure is promising for high frequency and high power applications owing to the superior material properties together with the reduced gate leakage current. In this paper, we present a novel AlGaN/GaN MIS-HFET using so-called in-situ SiN as a gate insulator. The in-situ SiN with a crystalline structure is formed subsequently after the epitaxial growth in the same reactor without any exposure in the air. The formation of the in-situ SiN greatly enhanced the sheet carrier concentration, which helps the reduction of the parasitic resistances. The fabricated MIS- HFET exhibits very high maximum oscillation frequency (f_max) of 203 GHz for the device with the gate length of 100 nm. The device exhibits the off-state breakdown voltages of 190 V at highest maintaining the high f_max over 190 GHz, and is thus promising for high frequency and high power applications including future millimeter wave communication systems.