High Mobility Multiple-Channel AlScN/GaN Heterostructures

TL;DR

This study demonstrates ultra-low sheet resistance in multi-channel AlScN/GaN heterostructures with high electron mobility, advancing GaN-based transistor technology for high-frequency electronics.

Contribution

It introduces multi-channel AlScN/GaN heterostructures with record-low sheet resistance and high mobility, using novel interlayer schemes and structural characterization.

Findings

Achieved sheet resistance as low as 13 Ω/□ at 2 K in five-channel structures.

Electron mobility up to 4160 cm²/V·s at 77 K in optimized single-channel structures.

Structural analysis shows pseudomorphic growth with minimal impact from barrier relaxation.

Abstract

Aluminum scandium nitride (AlScN) is a promising barrier material for gallium nitride (GaN)-based transistors for the next generation of radio-frequency electronic devices. In this work, we examine the transport properties of two dimensional electron gases (2DEGs) in single- and multi-channel AlScN/GaN heterostructures grown by molecular beam epitaxy, and demonstrate the lowest sheet resistance among AlScN-based systems reported to date. Assorted schemes of GaN/AlN interlayers are first introduced in single-channel structures between AlScN and GaN to improve conductivity, increasing electron mobility up to $1370$ cm$^{2}$/V$\cdot$s at 300 K and $4160$ cm$^{2}$/V$\cdot$s at 77 K, reducing the sheet resistance down to 170 $\Omega/\square$ and 70 $\Omega/\square$ respectively. These improvements are then leveraged in multi-channel heterostructures, reaching sheet resistances of 65 $\Omega/\square$ for three channels and 45 $\Omega/\square$ for five channels at 300 K, further reduced to 21 $\Omega/\square$ and 13 $\Omega/\square$ at 2 K, respectively, confirming the presence of multiple 2DEGs. Structural characterization indicates pseudomorphic growth with smooth surfaces, while partial barrier relaxation and surface roughening are observed at high scandium content, with no impact on mobility. This first demonstration of ultra-low sheet resistance multi-channel AlScN/GaN heterostructures places AlScN on par with state-of-the-art multi-channel Al(In)N/GaN systems, showcasing its capacity to advance existing and enable new high-speed, high-power electronic devices.