$f_{T}$ and $f_{\rm MAX}$ of 47 and 81 GHz , Respectively, on N-Polar GaN/AlN MIS-HEMT

Abstract

In this letter, we demonstrate the record small-signal performance from N-polar GaN-based metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs) by using a GaN spacer structure with an AlN barrier to reduce alloy scattering. High Si doping in GaN without excessive surface roughening has been achieved using a digital doping scheme. A low ohmic contact resistance of 0.16 ¿ · mm was measured. Submicrometer gates were fabricated by electron-beam lithography using a triple-layer resist process. <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> and <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> of 47 and 81 GHz, respectively, were obtained for the 150-nm-gate-length device. Further analysis has been done to understand the effect of access resistance on the high-frequency performance, defining a pathway for getting a higher gain and thus achieving a better high-frequency performance from N-polar GaN-based HEMTs.