A High RF-Performance AlGaN/GaN HEMT With Ultrathin Barrier and Stressor In Situ SiN

The submicrometer gate HEMT is fabricated with an ultrathin-barrier (UTB) AlGaN/gallium nitride (GaN) combined with in situ SiN passivation. The sheet resistance of the UTB Al $ _{0.2}$ Ga $ _{0.8}$ N (4 nm)/GaN heterostructure is effectively reduced by the SiNₓ passivation layer grown by metal organic chemical vapor deposition (MOCVD), from 6500 to 312 Ω / □. With the 20-nm stress-engineered in situ SiN, the device not only provides a large output current of 1.05 A/mm but also demonstrates promising potential on the RF applications, which gives AlGaN material two records high cutoff frequency f $_{T}$ /f $_{max}$ of 157 GHz/334 GHz for 100-nm gated device and 211 GHz/379 GHz for 70-nm gated device. During the continuous wave (CW) power measurement at 30 GHz, the 70-nm devices exhibit a large output power of 4.6 W/mm associated with a peak power-added efficiency (PAE) of 48.1% and a gain of 11.6 dB (V $_{ds}$ = 20 V), and a high PAE of 53.8% with an output power density of 1.9 W/mm and a gain of 10.8 dB (V $_{ds}$ = 10 V), respectively. The huge potential of the UTB-AlGaN/GaN is demonstrated for high-frequency and large-output power applications when it is combined with the in situ SiN, which is necessary for future communication systems.