In sub (0.5) (Al sub x Ga sub (1-x)) sub (0.5) P HEMT's for High-Efficiency Low-Voltage Power Amplifiers: Design, Fabrication and Device Results

In sub (0.5) (Al sub x Ga sub (1-x) sub (0.5) P HEMT's are expected to have higher two-dimensional electron gas density and larger current drive capability than both Al sub (0.23) Ga sub (0.77) As and In sub (0.5) Ga sub (0.5) P HEMT's due to the improved conduction band offsets. In this work, we performed a systematic investigation of the electrical properties of In sub (0.5) (Al sub x Ga sub (1-x) sub (0.5) P (= x =1) material system lattice-matched to GaAs. By considering the conduction band offset, direct-to-indirect band electron transfer, donor-related deep levels, and Schottky barrier height, a relatively narrow range of the Al content (0.2 = x =0. 3 was found to be the optimum for the design of In sub (0.5) (Al sub x Ga sub (1-x)) sub (0.5) P HEMT's. Under 1.2V operation, power transistors with the optimum aluminum composition show high drain current density, high transconductance, and excellent power-added efficiency (65. 2% at 850 MHz). These results demonstrate that InAlGaP HEMT's are promising candidates for high-efficiency low-voltage power applications.