[Paper Review] Electronic structure of InAs and InSb surfaces: density functional theory and angle-resolved photoemission spectroscopy

Shuyang Yang, Niels B. M. Schröter+11 more|arXiv (Cornell University)|Dec 29, 2020

Electronic and Structural Properties of Oxides71 references8 citations

TL;DR

This study combines density functional theory (DFT) with machine-learned Hubbard U corrections and angle-resolved photoemission spectroscopy (ARPES) to investigate the electronic structure of InAs and InSb surfaces. It demonstrates that DFT+U(BO) accurately predicts surface states and band bending, revealing that InAs(111) oxidation induces significant band bending and electron pockets due to strong As–O charge transfer, while InSb(110) oxidation causes minimal band modification, highlighting key differences in surface oxide behavior critical for topological quantum devices.

ABSTRACT

The electronic structure of surfaces plays a key role in the properties of quantum devices. However, surfaces are also the most challenging to simulate and engineer. Here, we study the electronic structure of InAs(001), InAs(111), and InSb(110) surfaces using a combination of density functional theory (DFT) and angle-resolved photoemission spectroscopy (ARPES). We were able to perform large-scale first principles simulations and capture effects of different surface reconstructions by using DFT calculations with a machine-learned Hubbard U correction [npj Comput. Mater. 6, 180 (2020)]. To facilitate direct comparison with ARPES results, we implemented a "bulk unfolding" scheme by projecting the calculated band structure of a supercell surface slab model onto the bulk primitive cell. For all three surfaces, we find a good agreement between DFT calculations and ARPES. For InAs(001), the simulations clarify the effect of the surface reconstruction. Different reconstructions are found to produce distinctive surface states. For InAs(111) and InSb(110), the simulations help elucidate the effect of oxidation. Owing to larger charge transfer from As to O than from Sb to O, oxidation of InAs(111) leads to significant band bending and produces an electron pocket, whereas oxidation of InSb(110) does not. Our combined theoretical and experimental results may inform the design of quantum devices based on InAs and InSb semiconductors, e.g., topological qubits utilizing the Majorana zero modes.

Motivation & Objective

• To understand the electronic structure of InAs(001), InAs(111), and InSb(110) surfaces, which are critical for topological quantum devices.
• To address the challenge of simulating surface reconstructions and oxidation effects in narrow-gap III-V semiconductors with high accuracy and efficiency.
• To validate a machine-learned Hubbard U correction (U_eff) in DFT for surface systems by comparing with ARPES experiments.
• To clarify how surface reconstructions and oxidation influence Fermi-level pinning, band bending, and surface states in InAs and InSb.
• To provide a reliable theoretical-experimental framework for guiding the design of high-quality semiconductor-superconductor heterostructures for Majorana zero modes.

Proposed method

• Employed DFT with a machine-learned Hubbard U correction (U_eff) determined via Bayesian optimization to reproduce HSE hybrid functional results for bulk InAs and InSb.
• Used a PBE+U(BO) approach to enable large-scale DFT simulations of surface slab models with several hundred atoms, overcoming the computational cost of HSE.
• Implemented a 'bulk unfolding' scheme to project the band structure of supercell surface slabs onto the bulk primitive Brillouin zone for direct comparison with ARPES data.
• Performed ARPES experiments on InAs(001), InAs(111), and InSb(110) surfaces to obtain experimental band dispersions and surface state information.
• Analyzed the effects of surface reconstructions (e.g., 2×4, 4×2, c(4×4)) and oxidation on band structure, Fermi-level pinning, and charge redistribution.
• Compared DFT+U(BO) predictions with ARPES data to validate the method and extract insights into surface electronic properties.

Experimental results

Research questions

• RQ1 How does the surface reconstruction of InAs(001) influence its electronic structure and surface state formation?
• RQ2 What is the impact of oxidation on the band bending and Fermi-level pinning in InAs(111) and InSb(110) surfaces?
• RQ3 Why does InAs(111) oxidation lead to electron pocket formation while InSb(110) oxidation does not?
• RQ4 To what extent can machine-learned U_eff values derived from bulk materials be reliably transferred to surface slab models?
• RQ5 How does the charge transfer from surface atoms (As vs. Sb) to oxygen differ in native oxides, and what are the resulting electronic consequences?

Key findings

• The DFT+U(BO) method successfully reproduces ARPES data for all three surfaces, confirming the transferability and accuracy of machine-learned U_eff values to surface systems.
• For InAs(001), the c(4×4) reconstruction is predicted to host a surface state at the valence band maximum, but this is not observed in ARPES, supporting coexisting 2×4 and 4×2 reconstructions.
• InAs(111) oxidation leads to significant band bending and the formation of an electron pocket due to strong charge transfer from As to O, as confirmed by both ARPES and DFT.
• InSb(110) oxidation shows minimal effect on the valence band maximum and does not produce an electron pocket, indicating weaker charge transfer from Sb to O.
• The difference in behavior arises from greater sub-surface charge redistribution in InAs(111) oxides compared to InSb(110), explaining the preferential charge accumulation in InAs native oxides.
• The results demonstrate that native oxides of InAs promote charge accumulation and band bending, while InSb oxides exhibit gap pinning, which has direct implications for tunnel junctions and Majorana mode coupling in quantum devices.