AlGaN/GaN HEMTs Fabricated on Selectively Grown Mesas on Si(111)

AlGaN/GaN HEMT devices on selectively grown mesa structures on Si(111) have been grown and fabricated. A typical strain relief structure was grown over the entire 2" wafer. Subsequently, the epilayer was removed from most of the wafer surface by dry etching, leaving only the patterned mesas intact. Then, the wafer was returned to the growth chamber and the growth of the AlGaN/GaN heterostructure was completed. GaN does not nucleate on the Si(111) surface, thus the growth was highly selective, and moreover, due to the small size of the mesas, was crack-free. A five level mask set, consisting of mesa, ohmic, gate, passivation, and interconnect metal levels was used to complete the working devices. Devices with 0.8 µm gate length showed peak currents of 0.45 A/mm, and transconductance of 130 mS/mm. The devices were essentially free of current collapse and had fT of 9 GHz and fMAX of 22 GHz.