Thermally stable carbon-related centers in 6H-SiC: photoluminescence spectra and microscopic models

TL;DR

This study combines experimental photoluminescence spectra with ab initio calculations to identify and model thermally stable carbon-related centers in 6H-SiC, confirming the (C_3)_Si defect as the U-center and proposing the (C_2)_Hex as a model for other centers.

Contribution

It provides experimental validation of theoretical models for carbon-related defects in 6H-SiC, including isotope splitting analysis and microscopic defect models.

Findings

Confirmed low-energy vibrational mode for U-center

Achieved near-perfect isotope splitting agreement for (C_3)_Si

Discovered discrepancy of about 10 meV in local mode energies for (C_2)_Hex

Abstract

Recent ab initio calculations [Mattausch et al., Phys. Rev. B 70, 235211 (2004)] of carbon clusters in SiC reveal a possible connection between the tricarbon antisite (C_3)_Si and the U photoluminescence center in 6H-SiC [Evans et al., Phys. Rev. B 66, 35204 (2002)]. Yet, some of the predicted vibrational modes were not observed experimentally. Here we report experiments which indeed confirm the existence of a low-energy mode for the U-center (as well as for the HT3- and HT4-centers with spectral details similar to the U-center). We calculated the isotope splitting for the (C_3)_Si-defect and found near-perfect agreement with our data. In addition, we discuss the carbon di-interstitial (C_2)_Hex as a model for the Z- and HT5-centers. The isotope splitting is also well reproduced, but the absolute values of the local mode energies show a discrepancy of about 10 meV.