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We report the design, fabrication and characterization of metamorphic high electron-mobility transistors (MHEMTs) with self-aligned ohmic electrodes. In this work, asymmetrically recessed 50-nm Γ-gates have been successfully used as the shadow mask for ohmic metal deposition. Extremely high extrinsic transconductance over a wide drain bias from 0.1 to 1.25 V can be made possible by fabricating devices with small gate-source spacing, small source-drain spacing, and the non-alloyed ohmic. Measured maximum extrinsic transconductance of 3 S/mm is a new record for all HEMT devices on GaAs and equals the best results from InP -based HEMTs. The same devices also show a voltage gain of 22, maximum stable gain of 10.8 dB at 110 GHz, and breakdown voltage of 4.3 V, which all are the highest among any self-aligned HEMTs based on InGaAs channel. The outstanding performance is the result of the seamless integration of the asymmetric gate recess and Γ-gate-based self-aligned ohmic process.

This paper reports a successful improvement of the low breakdown voltages in short gate-length metamorphic high electron-mobility transistors. The technical approach includes both the optimization of the epitaxial layer design and the selection of the proper gate recess scheme. By employing a novel epitaxial design (including a high indium composite channel and the double-sided doping) and an asymmetric gate recess, both the off-state and on-state breakdown voltages have been improved for 50-nm high-performance metamorphic high electron-mobility transistors. The results reported herein demonstrate that these devices are excellent candidates for ultra-high-frequency power applications.

BAE Systems has developed a high power, high yield 70nm 6" 2-mil PHEMT MMIC process for frequencies up to 100GHz. Utilizing T -gate technology and 2-mil substrates, we have created a millimeter wave technology that produces excellent performance from Ka -band through W -bands. The device DC and RF characteristics have excellent uniformity across the wafer. In this paper, we report the 70nm device fabrication on 6-inch wafers and compare the DC and RF characteristics with its mature 0.1µm counterpart.

High power AlGaN/GaN HEMTs on free-standing GaN substrates with excellent stability have been demonstrated for the first time. When operated at a drain bias of 50V, devices without a field plate showed a record CW output power density of 10.0W/mm at 10GHz with an associated power-added efficiency of 45%. The efficiency reaches a maximum of 58% with an output power density of 5.5W/mm under a drain bias of 25V at 10GHz. Long-term stability of device RF operation was also examined. Under ambient conditions, devices biased at 25V and driven at 3dB gain compression remained stable at least up to 1,000 hours, degrading only by 0.35dB in output power. Such results clearly demonstrate the feasibility of GaN - on - GaN HEMT as an alternative device technology to the GaN - on - SiC HEMT in supporting reliable, high performance microwave power applications.