AlGaN/GaN HEMT With a Transparent Gate Electrode

Abstract

AlGaN/GaN high-electron-mobility transistors (HEMTs) with indium tin oxide (ITO) transparent gate electrodes have been fabricated. The transparent gate electrodes enable the investigation of photon, electron, and phonon behaviors in active regions in HEMTs using optical characterizations such as electroluminescence, photoluminescence, and Raman spectroscopy technologies. Leakage current, on/off ratio, and transparency have been compared for transistors using Ni/Au/Ni, ITO, and Ni/ITO stacks as gate electrodes. Compared to the Ni/Au/Ni gate transistor, the ITO gate device shows a comparable current gain cutoff frequency ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> ) but a much lower power gain cutoff frequency ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> ) due to the low conductivity of ITO.