Electronic structure of Humble defects in Ge and Ge$_{0.8}$Si$_{0.2}$

TL;DR

This study combines first-principles calculations and electron energy loss spectroscopy to analyze the electronic structure of Humble planar defects in germanium and GeSi alloys, revealing their impact on band gap properties.

Contribution

It provides the first detailed electronic structure analysis of Humble defects in Ge and GeSi alloys using density functional theory and spectroscopic measurements.

Findings

Humble defects tend to enlarge the electronic band gap.

Core-hole effects are essential for accurate spectral reproduction.

Spectroscopic fingerprints of local bonding environments are identified.

Abstract

The group-IV diamond-structure elements are known to host a variety of planar defects, including {001} planar defects in C and {001}, {111} and {113} planar defects in Si and Ge. Among the {001} planar defects, the Humble defect, known for some time to occur in Ge, has recently also been observed in Si/Ge alloys, but the details of its electronic structure remain poorly understood. Here we perform first-principles density functional calculations to study Humble defects in both Ge and Ge$_{0.8}$Si$_{0.2}$. We also measure the Si L$_{2,3}$-edge electron energy loss spectra both at the defect and in a bulk-like region far from the defect, and compare with theoretical calculations on corresponding Si sites in our first-principles calculations. We find that inclusion of core-hole effects in the theory is essential for reproducing the observed L$_{2,3}$ edge spectra, and that once they are included, the results provide a set of fingerprints for different types of local atomic bonding environments in Ge$_{0.8}$Si$_{0.2}$. Our first-principles calculations reveal that the Humble defects have a tendency to enlarge the electronic band gap, which may have potential uses in band engineering. The use of hybrid functionals for an improved description of the band gap in these systems is also discussed.