A QM/MM equation-of-motion coupled-cluster approach for predicting semiconductor color-center structure and emission frequencies

TL;DR

This paper presents a combined QM/MM and EOMCC approach to accurately predict the structure and emission spectra of silicon-vacancy defects in silicon carbide, validated against experimental photoluminescence data.

Contribution

It introduces a novel computational framework integrating SIMOMM with EOMCC methods for precise defect characterization in semiconductors.

Findings

EOMCC methods reliably predict defect charge states and spectra within 0.1 eV.

The approach accurately reproduces experimental photoluminescence peaks.

Extension to transition-metal defects demonstrates broad applicability.

Abstract

Valence excitation spectra are computed for all deep-center silicon-vacancy defect types in 3C, 4H, and 6H silicon carbide (SiC) and comparisons are made with literature photoluminescence measurements. Nuclear geometries surrounding the defect centers are optimized within a Gaussian basis-set framework using many-body perturbation theory or density functional theory (DFT) methods, with computational expenses minimized by a QM/MM technique called SIMOMM. Vertical excitation energies are subsequently obtained by applying excitation-energy, electron-attached, and ionized equation-of-motion coupled-cluster (EOMCC) methods, where appropriate, as well as time-dependent (TD) DFT, to small models including only a few atoms adjacent to the defect center. We consider the relative quality of various EOMCC and TD-DFT methods for (i) energy-ordering potential ground states differing incrementally in charge and multiplicity, (ii) accurately reproducing experimentally measured photoluminescence peaks, and (iii) energy-ordering defects of different types occurring within a given polytype. The extensibility of this approach to transition-metal defects is also tested by applying it to silicon-substitutional chromium defects in SiC and comparing with measurements. It is demonstrated that, when used in conjunction with SIMOMM-optimized geometries, EOMCC-based methods can provide a reliable prediction of the ground-state charge and multiplicity, while also giving a quantitative description of the photoluminescence spectra, accurate to within 0.1 eV of measurement in all cases considered.