First principles calculations of band offsets at heterovalent $\varepsilon$-Ge/In$_x$Al$_{1-x}$As interfaces

TL;DR

This study uses first principles calculations to explore how interface structure and composition affect band offsets at Ge/InAlAs heterovalent interfaces, revealing significant variability influenced by local atomic arrangements.

Contribution

It provides detailed insights into the sensitivity of band offsets to interfacial and substrate stoichiometry, highlighting the potential for chemical control of electronic properties.

Findings

Band offsets vary significantly with interface structure and stoichiometry.

Valence and conduction band offsets can change type due to local structural variations.

Diffusion of species across the interface causes approximately linear changes in band offsets.

Abstract

First principles electronic structure calculations are carried out to investigate the band alignments of tensile strained (001) Ge interfaced with (001) In$_{x}$Al$_{1-x}$As. The sensitivities of band offsets to interfacial structure, interfacial stoichiometry, and substrate stoichiometry, are investigated. Large qualitative variations of the valence and conduction band offsets are observed, including changes of the band offset type, indicating the importance of local structural variations of the interface for band offsets in real samples. Our results explain recent measurements of band offsets derived from XPS core level spectra in terms of As atoms penetrating through the first few monolayers of the Ge film. Analogous studies are carried out for the diffusion of other species across the interface, and in general the band offsets vary approximately linearly with diffusion depth relative to the values for pristine "sharp" interfaces, where the sign of the linear variation depends on the diffusing species. This large sensitivity of the band alignments to interface details indicates potential routes to chemically control the band offset of this group IV/III-V interface by tuning the stoichiometry of the substrate surface that the thin film is grown on.