Band Anticrossing in Dilute Germanium Carbides Using Hybrid Functionals

TL;DR

This study uses advanced hybrid functional simulations to analyze the electronic band structure of dilute germanium carbides, revealing deviations from traditional models and identifying the composition threshold for bandgap closure.

Contribution

It provides the first ab initio analysis of Ge1-xCx using HSE06 functionals, showing how the band structure evolves with C content without defects.

Findings

Conduction band minimum decreases with increasing C content.

Bandgap vanishes at C content x>0.017.

Deviations from the band anticrossing model near the Brillouin zone center.

Abstract

Dilute germanium carbides (Ge1-xCx) offer a direct bandgap for compact silicon photonics, but widely varying results have been reported. This work uses ab initio simulations with HSE06 hybrid functionals and spin-orbit coupling to study the Ge1-xCx band structure behavior in the absence of defects. Contrary to Vegard's law, the conduction band minimum at k=0 is consistently found to decrease with increasing C content, while L and X valleys change much more slowly. A vanishing bandgap was observed for all alloys with x>0.017. Conduction bands deviate from a constant-potential band anticrossing model except near the center of the Brillouin zone.