In/sub 0.5/(Al/sub x/Ga/sub 1-x/)/sub 0.5/ HEMTs 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/ high electron-mobility transistors (HEMTs) 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 HEMTs due to the improved conduction-band offsets. In this paper, 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 (0/spl les/x/spl les/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/spl les/x/spl les/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/ HEMTs. Under 1.2-V 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 HEMTs are promising candidates for high-efficiency low-voltage power applications.