3-mm double-heterojunction microwave power HEMT fabricated by selective RIE

Current-voltage and initial RF measurements are presented on a double-heterojunction HEMT (high-electron-mobility transistor) structure designed for power MMIC applications. The device structure is grown by molecular-beam epitaxy and uses a spatially variant superlattice to improve the performance of the inverted AlGaAs/GaAs interface. Gate recessing is achieved using a hybrid wet-chemical selective dry etching process. For selective dry etching, reactive ion etching with a >600:1 selectivity for GaAs over AlGaAs is used to control the recess depth. The room temperature DC characteristics for a 3-mm power FET (0.7- mu m gate) display an I/sub dss/ of 370 mA/mm, a peak transconductance of 180 mS/mm, and a maximum gate-to-drain breakdown of 22 V. Large-signal microwave measurements at 5.5 GHz yielded a saturated output power of 1.3 W (31.2 dBm), 8.3-dB large-signal gain, and a peak power-added efficiency of 55%.<
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