# Structural, electronic, and optical properties of the C-C complex in bulk silicon from first principles

## TL;DR

This study uses first-principles calculations to analyze the structural, electronic, and optical properties of different configurations of the CiCs complex in silicon, clarifying previous experimental ambiguities and highlighting the C-form's potential role in light emission.

## Contribution

It provides a detailed theoretical analysis of four possible CiCs configurations in silicon, clarifying their structures and optical roles using DFT and MBPT methods.

## Key findings

- The C-form was previously misidentified as B-form in some experiments.
- A- and B-forms are unlikely to contribute to light emission.
- The C-form may be significant in heavily carbon-doped silicon.

## Abstract

The structure of the CiCs complex in silicon has long been the subject of debate. Numerous theoretical and experimental studies have attempted to shed light on the properties of these defects that are at the origin of the light emitting G-center. These defects are relevant for applications in lasing, and it would be advantageous to control their formation and concentration in bulk silicon. It is therefore essential to understand their structural and electronic properties. In this paper, we present the structural, electronic, and optical properties of four possible configurations of the CiCs complex in bulk silicon, namely the A-, B-, C-, and D-forms. The configurations were studied by density functional theory (DFT) and many-body perturbation theory (MBPT). Our results suggest that the C-form was misinterpreted as a B-form in some experiments. Our optical investigation also tends to exclude any contribution of A- and B-forms to light emission. Taken together, our results suggest that the C-form could play an important role in heavily carbon-doped silicon.