抄録
We investigated the resistivity of Ti/Al contact to n-AlGaN/GaN heterostructures changing the annealing temperature and the Al-fraction for high performance short channel FETs. A low resistivity of 1×10-7 Ω cm2 was obtained at an annealing temperature of 650°C with a 10nm Ti and 200nm Al structure for 1019cm-3 doped n-AlGaN/GaN. The mechanism of ohmic contact is studied by TEM observation. Surface oxide is removed when the thin Ti layer makes Al3Ti grains during 650°C annealing. After the oxide is removed, pure Al metal makes a low resistance contact to AlGaN/GaN heterostructures. K-Band Microwave performance of AlGaN/GaN HJFETs grown by MOVPE on sapphire substrate is also reported. A 0.25-μm T-shaped gate is fabricated by two-layer resist process using electron-beam lithography. The fabricated devices have an intrinsic cut-off frequency fT of 57GHz and an intrinsic maximum oscillation frequency fmax of 114GHz. The continuous wave output power density is 1.58W/mm with 5.9dB of gain and 11% power added efficiency at 25GHz. This output power density is about two times higher than GaAs-based pseudomorphic FETs.
