High Electron Velocity Submicrometer AlN/GaN MOS-HEMTs on Freestanding GaN Substrates

Abstract

AlN/GaN heterostructures with 1700-cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /V·s Hall mobility have been grown by molecular beam epitaxy on freestanding GaN substrates. Submicrometer gate-length (L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> ) metal-oxide-semiconductor (MOS) high-electron-mobility transistors (HEMTs) fabricated from this material show excellent dc and RF performance. L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> = 100 nm devices exhibited a drain current density of 1.5 A/mm, current gain cutoff frequency f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> of 165 GHz, a maximum frequency of oscillation f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">max</sub> of 171 GHz, and intrinsic average electron velocity v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> of 1.5 ×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">7</sup> cm/s. The 40-GHz load-pull measurements of L <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">G</sub> = 140 nm devices showed 1-W/mm output power, with a 4.6-dB gain and 17% power-added efficiency. GaN substrates provide a way of achieving high mobility, high v <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> , and high RF performance in AlN/GaN transistors.