A multienergy oxygen ion implantation process was demonstrated to be compatible with the processing of high-power microwave AlGaN/GaN high electron mobility transistors (HEMTs). HEMTs that are isolated by this process exhibited gate-lag- and drain-lag-free operation. A maximum output power density of 5.3 W/mm at Vgs = -4 V = Vds=50 and a maximum power added efficiency of 51.5% at V =-4 V Vds=30 at 3 GHz were demonstrated on HEMTs without field plates on sapphire substrate. This isolation process results in planar HEMTs, circumventing potential problems with enhanced gate leakage due to the gate contacting the 2-D electron gas at the mesa sidewall.
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