Rashba field in GaN

TL;DR

This paper investigates the Rashba spin-orbit coupling in bulk GaN and GaN/AlGaN heterostructures using microwave resonance experiments, revealing significant differences and a new surface electron resonance.

Contribution

It provides experimental evidence of weak Rashba coupling in bulk GaN and identifies the interface as the origin of strong Rashba fields in heterostructures.

Findings

Large difference in spin-orbit coupling between bulk and heterostructures.

Observation of coupled plasmon-cyclotron resonance without spin resonance.

Identification of a new electron spin resonance related to surface layers.

Abstract

We discuss problem of Rashba field in bulk GaN and in GaN/AlGaN two-dimensional electron gas, basing on results of X-band microwave resonance experiments. We point at large difference in spin-orbit coupling between bulk material and heterostructures. We observe coupled plasmon-cyclotron resonance from the two-dimensional electron gas, but no spin resonance, being consistent with large zero-field spin splitting due to the Rashba field reported in literature. In contrast, small anisotropy of g-factor of GaN effective mass donors indicates rather weak Rashba spin-orbit coupling in bulk material, not exceed 400 Gauss, alpha_BIA < 4*10^-13 eVcm. Furthermore, we observe new kind of electron spin resonance in GaN, which we attribute to surface electron accumulation layer. We conclude that the sizable Rashba field in GaN/AlGaN heterostructures originates from properties of the interface.