Phonon-assisted optical absorption of SiC polytypes from first principles

Silicon carbide (SiC) is an indirect-gap semiconductor material widely used in electronic and optoelectronic applications. While experimental measurements of the phonon-assisted absorption coefficient of SiC across its indirect gap have existed for more than 50 years, theoretical investigations of phonon-assisted absorption have been hampered by their excessive computational cost. In this work, we calculate the phonon-assisted temperature-dependent optical absorption spectra of the commonly occurring SiC polytypes (3C, 2H, 4H, 6H, and 15R), using first-principles approaches based on density functional theory and related techniques. We show that our results agree with experimentally determined absorption coefficients in the spectral region between the direct and indirect band gaps. The temperature dependence of the spectra can be well predicted with taking the temperature dependence of the band gaps into account. Lastly, we compare the spectra obtained with second-order perturbation theory to those determined by the special displacement method and we show that the full consideration of the electronic energy renormalization due to temperature is important to further improve the prediction of the phonon-assisted absorption in SiC. Our insights can be applied to predict the optical spectra of the less common SiC polytypes and other indirect-gap semiconductors in general.

Automated summary

Silicon carbide (SiC) is widely used in electronic and optoelectronic applications as an indirect-gap semiconductor material. The computational cost has hindered theoretical investigations of phonon-assisted absorption, despite the existence of experimental measurements for more than 50 years. In this study, we calculate the temperature-dependent optical absorption spectra of common SiC polytypes using first-principles approaches. Our results agree with experimental absorption coefficients and predict the temperature dependence by considering the band gap. Considering the electronic energy renormalization due to temperature is important for improving the prediction of phonon-assisted absorption in SiC. Our insights can be applied to predict the optical spectra of other indirect-gap semiconductors and less common SiC polytypes in general.