High-performance double-recessed enhancement-mode metamorphic HEMTs on 4-in GaAs substrates

Enhancement-mode InAlAs/InGaAs/GaAs metamorphic HEMTs with a composite InGaAs channel and double-recessed 0.15-μm gate length are presented. Epilayers with a room-temperature mobility of 10 000 cm
²
/V-s and a sheet charge of 3.5×10/sup 12/cm/sup -2/ are grown using molecular beam epitaxy on 4-in GaAs substrates. Fully selective double-recess and buried Pt-gate processes are employed to realize uniform and true enhancement-mode operation. Excellent dc and RF characteristics are achieved with threshold voltage, maximum drain current, extrinsic transconductance, and cutoff frequency of 0.3 V, 500 mA/mm, 850 mS/mm, and 128 GHz, respectively, as measured on 100-μm gate width devices. The load pull measurements of 300-μm gate width devices at 35 GHz yielded a 1-dB compression point output power density of 580 mW/mm, gain of 7.2 dB, and a power-added efficiency of 44% at 5 V of drain bias.