First-Principles Prediction of Optical Absorption Enhancement for Si Native Defect Clusters under Biaxial Strain

Abstract

We use density-functional theory calculations to qualitatively explore the effects of fourfold-coordinated vacancy V4 and interstitial I4 clusters on optical absorption spectra in crystalline Si c-Si under selected conditions of biaxial strain =� 3, 0, and 3%. While both native defect clusters enhance c-Si absorption by redshifting the absorption edge, we observe additional enhancement from biaxial strain. Increased strain magnitude tends to increase the absorption enhancement effect, but the optimal sign of strain exhibits a complementary relationship: compressive strain most effectively enhances V4 absorption, while tensile strain most effectively enhances I4 absorption. The absorption redshift as a function of strain correlates well with effective bandgap reduction, including the appearance of an intermediate band under certain conditions = �3 and 0% for V4. Our results suggest that manipulation of native defect distributions and their strain fields can be used to engineer the Si absorption spectra.