Silicon dioxide (SiO 2) was used in the fabrication of the recessed platinum/titanium/platinum/gold T-gate. The fabricated HEMTs featured titanium/molybdenum/titanium/platinum/gold ohmic source/drain contacts scaled down to 0.8Ојm separation. In the HEMT, the effective mobility was only slightly impacted at 13,200cm 2/V-s the average electron velocity under the gate was 6.2x10 7cm/s. Hall-mobility measurements at a two-dimensional electron gas (2DEG) concentration of ~3x10 12/cm 2 showed an increase in mobility for the composite channel to 13,500cm 2/V-s, compared with 10,500cm 2/V-s for the more conventional channel. The upper layers included a 3nm InP etch stop between the barrier and the heavily doped multi-layer cap.ДЇigure 1: (a) HEMT schematic with two types of QW channel, (b) conduction-band profile in equilibrium under gate at 0.2V over threshold for both channel designs, and (c) cross-sectional scanning/transmission electron microscope (SEM/TEM) images of fabricated T-gate before and after gate metallization. The buffer consisted of 200nm In 0.52Al 0.48As. The material was grown on 3-inch indium phosphide (InP) substrate. The researchers compared devices with a composite quantum well channel (Figure 1) with a more conventional In 0.7Ga 0.3As channel. The team sees renewed interest in InGaAs devices for future electronics, such as quantum computing and beyond-5G deployment, based on the potential for lower noise performance from the combination of high f T and low source resistance. However, the latter device also featured a maximum oscillation frequency (f max) of more than 1THz (1000GHz), while the new device only achieved 492GHz. The 738GHz figure compares with a previous InGaAs HEMT with 710GHz cut-off.

The team credits a composite indium gallium arsenide (InGaAs) quantum well (QW) channel structure with enabling the record frequency high-electron-mobility transistor (HEMT). The result from Kyoungpook National University (KNU), University of Ulsan and Quantum Semiconductor International Co Ltd in South Korea and NTT Device Technology Laboratories in Japan was presented online at the International Electron Devices Meeting (IEDM) at the end of 2020. 4 February 2021 Transistor cut-off frequency at 738GHzДЄ research team in Korea and Japan has reported field-effect transistors (FETs) with a cut-off frequency of 738GHz, claiming this as вЂњthe highest f T of any FET with any material systemвЂќ.

What is cut off frequency