k-Space imaging of anisotropic 2D electron gas in GaN/GaAlN high-electron-mobility transistor heterostructures

TL;DR

This study uses advanced angle-resolved photoelectron spectroscopy to visualize the electronic structure of 2D electron gas in GaN/AlGaN heterostructures, revealing anisotropic properties linked to high-field transport behavior.

Contribution

It introduces a novel application of soft-X-ray ARPES to directly image the k-space electronic structure of GaN/AlGaN HEMTs, uncovering anisotropic Fermi surfaces and effective masses.

Findings

Discovery of significant planar anisotropy in the Fermi surface.

Identification of anisotropic effective mass related to atomic relaxation.

Correlation between electronic anisotropy and high-field transport properties.

Abstract

Nanostructures based on buried interfaces and heterostructures are at the heart of modern semiconductor electronics as well as future devices utilizing spintronics, multiferroics, topological effects and other novel operational principles. Knowledge of electronic structure of these systems resolved in electron momentum k delivers unprecedented insights into their physics. Here, we explore 2D electron gas formed in GaN/AlGaN high-electron-mobility transistor (HEMT) heterostructures with an ultrathin barrier layer, key elements in current high-frequency and high-power electronics. Its electronic structure is accessed with angle-resolved photoelectron spectroscopy whose probing depth is pushed to a few nm using soft-X-ray synchrotron radiation. The experiment yields direct k-space images of the electronic structure fundamentals of this system: the Fermi surface, band dispersions and occupancy, and the Fourier composition of wavefunctions encoded in the k-dependent photoemission intensity. We discover significant planar anisotropy of the electron Fermi surface and effective mass connected with relaxation of the interfacial atomic positions, which translates into non-linear (high-field) transport properties of the GaN/AlGaN heterostructures as an anisotropy of the saturation drift velocity of the 2D electrons.