HEMT With Ultralow Contact Resistance by Room Temperature Process With One-Step EBL T-Shape Gates for Subterahertz Applications: Design, Fabrication, and Characterization

We present the design, fabrication, and characterization of InGaAs channel high electron mobility transistors (HEMTs) with ultralow contact resistance for millimeter-wave and subterahertz applications. The HEMT has a composite InGaAs channel and a 50-nm T-shaped gate, which was realized through a single-step electron beam lithography (EBL) process. A room temperature ohmic contact fabrication process achieving the lowest contact resistance of 15 mΩ·mm has been developed with all room temperature process. The I–V measurements of the HEMTs at room temperature revealed a peak drain current of 0.75 A/mm and a transconductance of 1.4 S/mm. In standard 50-Ω S-parameter measurements, the HEMTs exhibited a maximum gain of 10 dB at 170 GHz. However, utilizing an active load–pull measurement, the 50-nm HEMT shows a gain of 14.5 dB at 170 GHz and 2 dB at 270 GHz. The load–pull measurements also obtained power added efficiency (PAE) and 1-dB compression point of the HEMTs. The noise performance was characterized using a noise parameter system with source tuner between 2 and 50 GHz. A drift-diffusion model was used to benchmark the dc and RF performance of the devices, and good agreements have been achieved.