Mobility-Enhanced Nitrogen-Polar GaN/AlGaN Heterostructure by Stress Modulation

Nitrogen-polar (N-polar) GaN/AlGaN heterostructures hold tremendous promise for the fabrication of high-frequency millimeter-wave high electron mobility transistors (HEMTs). However, the preparation of N-polar GaN/AlGaN heterostructures with high two-dimensional electron gas (2DEG) mobility remains challenging. In this work, we demonstrate that the stress state of the epitaxial heterostructures plays a critical role in modulating the 2DEG mobility. By engineering the stress state of the high-resistance N-polar GaN template from tensile stress to weak compressive stress, we observe a remarkable enhancement in room-temperature 2DEG mobility from 820 to 1420 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>/V·s. Importantly, through theoretical calculations, we elucidate the mechanism by which the stress state affects the 2DEG mobility. Moreover, we further boost the 2DEG mobility to 1730 cm<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup>/V·s by introducing a thin AlN interlayer at the GaN/AlGaN interface. This is a high mobility value reported for MOCVD-grown N-polar GaN/AlGaN heterostructures on SiC substrates. This work could promote the development of N-polar GaN/AlGaN based HEMTs with high frequency and high output power.