Non-parabolicity of the conduction band of wurtzite GaN

TL;DR

This study measures the effective electron mass in GaN heterostructures, revealing significant conduction band non-parabolicity explained by remote bands, and refines the band edge mass value by accounting for polaron effects.

Contribution

It provides precise measurements of the conduction band non-parabolicity in GaN and demonstrates the importance of remote bands in modeling the effective mass behavior.

Findings

Effective mass extrapolated to band edge: 0.208 m_e

Remote bands are essential for explaining non-parabolicity

Polaron corrections are negligible for this system

Abstract

Using cyclotron resonance, we measure the effective mass, $m$*, of electrons in AlGaN/GaN heterostructures with densities, $n_{2D}\sim 1-6\times10^{12}$cm$^{-2}$. From our extensive data, we extrapolate a band edge mass of $(0.208\pm0.002) m_e$. By comparing our $m$* data with the results of a multi-band \textbf{k.p} calculation we infer that the effect of remote bands is essential in explaining the observed conduction band non-parabolicity (NP). Our calculation of polaron mass corrections -- including finite width and screening - suggests those to be negligible. It implies that the behavior of $m*(n_{2D})$ can be understood solely in terms of NP. Finally, using our NP and polaron corrections, we are able to reduce the large scatter in the published band edge mass values.