Evaluation of Low-Temperature Saturation Velocity in β-(AlXGa1-X)2O3/Ga2O3 Modulation-Doped Field-Effect Transistors

We report on the high-field transport characteristics and saturation velocity in a modulation-doped beta-(AlxGa1-x)(2)O-3/Ga2O3 heterostructure. The formation of a 2-D electron gas (2DEG) in the modulation-doped structure was confirmed from the Hall measurements, and the 2DEG channel mobility increased from 143 cm(2)/V.s at room temperature to 1520 cm(2)/V.s at 50 K. The high electronmobility at 50 K made it feasible to achieve velocity saturation inside the channel. The saturation velocity was estimated based on both pulsed current-voltage measurements and small-signal radio frequency (RF) measurements. The measured velocity-field profile suggested a saturation velocity above 1.1 x 10(7) cm/s at 50 K. The small-signal RF characteristics were measured for the fabricated modulation-doped field-effect transistors with a Pt-based Schottky contact. The current gain cutoff frequency (f(t)) and maximum oscillation frequency (f(max)) showed significant increases from 4.0/11.8 GHz at room temperature to 17.4/40.8 GHz at 50K for the device with gate length of L-G = 0.61 mu m. The analysis of the low temperature f(t) based on device simulations indicated a peak velocity of 1.2 x 10(7) cm/s. The three-terminal off-state breakdown measurement further suggested an average breakdown field of 3.22 MV/cm. The high saturation velocity and high breakdown field in beta-Ga2O3 make it a promising candidate for high-power and high-frequency device applications.