Measurement of valence-band offsets of InAlN/GaN heterostructures grown by metal-organic vapor phase epitaxy

Abstract

The valence band offsets, $\Delta E_{\text{V}}$ , of ${\text{In}}_{0.17}{\text{Al}}_{0.83}\text{N}/\text{GaN}$ , ${\text{In}}_{0.25}{\text{Al}}_{0.75}\text{N}/\text{GaN}$ , and ${\text{In}}_{0.30}{\text{Al}}_{0.70}\text{N}/\text{GaN}$ heterostructures grown by metal-organic vapor phase epitaxy were evaluated by using x-ray photoelectron spectroscopy (XPS). The dependence of the energy position and the full width at half maximum of the $\text{Al}2p$ spectrum on the exit angle indicated that there was sharp band bending caused by the polarization-induced electric field combined with surface Fermi-level pinning in each ultrathin InAlN layer. The $\Delta E_{\text{V}}$ values evaluated without taking into account band bending indicated large discrepancies from the theoretical estimates for all samples. Erroneous results due to band bending were corrected by applying numerical calculations, which led to acceptable results. The evaluated $\Delta E_{\text{V}}$ values were $0.2\pm 0.2\text{eV}$ for ${\text{In}}_{0.17}{\text{Al}}_{0.83}\text{N}/\text{GaN}$ , $0.1\pm 0.2\text{eV}$ for ${\text{In}}_{0.25}{\text{Al}}_{0.75}\text{N}/\text{GaN}$ , and $0.0\pm 0.2\text{eV}$ for ${\text{In}}_{0.30}{\text{Al}}_{0.70}\text{N}/\text{GaN}$ . Despite the large decrease of around 1.0 eV in the band gap of InAlN layers according to the increase in the In molar fraction, the decrease in $\Delta E_{\text{V}}$ was as small as 0.2 eV. Therefore, the change in band-gap discontinuity was mainly distributed to that in conduction band offset.