XPS-Derived Band Alignment of Thermal-ALD HfO₂ on Cubic InN(001)

Abstract

Hafnium oxide/cubic indium nitride (HfO₂/β-InN) heterostructures were investigated to establish the band alignment of a high-κ dielectric on an ultrathin nonpolar InN channel. β-InN was grown on β-GaN/MgO(001) by plasma-assisted molecular beam epitaxy, followed by thermal atomic layer deposition of HfO₂ at 250 °C. Reflection high-energy electron diffraction evolved from streaked to spotty patterns, indicating a transition toward three-dimensional island growth. X-ray diffraction confirmed a predominantly cubic InN response with a weak wurtzite contribution, while no distinct crystalline HfO₂ reflections were resolved in the ultrathin heterostructure. Atomic force microscopy revealed comparable island-like surface morphology before and after oxide deposition, with RMS roughness values of 13.94 and 15.00 nm, respectively. The valence-band offset was determined by Kraut analysis of X-ray photoelectron spectroscopy core-level spectra and was approximately 1.6 eV. By combining this value with an HfO₂ band gap of 6.30 ± 0.20 eV and reported β-InN band-gap values of 0.61–0.89 eV, a derived conduction-band offset of approximately 3.8–4.1 eV was obtained. The resulting HfO₂/β-InN heterojunction exhibits a type-I band alignment with substantial barriers for carrier injection. These findings provide experimental band-alignment information for thermal-ALD HfO₂ on nonpolar cubic InN(001), while emphasizing that surface oxidation, electron accumulation, roughness, and XPS-related systematic uncertainty remain relevant considerations for device integration

Keywords: cubic InN/ HfO₂; atomic layer deposition; XPS