Point defects in BaSi2 identified and analyzed by electron paramagnetic resonance, photoluminescence and density functional theory

Barium disilicide (BaSi 2 ) is a semiconductor with promising photovoltaic properties. To build efficient devices, a good understanding of its defects is required. In this article, we present the first systematic study of such defects in a series of BaSi 2 samples synthetized in Barium-rich and Silicon-rich conditions. We combined electron paramagnetic resonance (EPR), Photoluminescence (PL) and density functional theory (DFT) to complete our analysis. With these techniques, we spectroscopically characterized five paramagnetic defect centers (defect 1 to defect 5) and four PL centers (P0 to P3). We identified several of them: in Ba-rich conditions, defect 5 corresponds to the negatively charged silicon vacancy V Si −1 . In Si-rich conditions, defect 1 and defect 2 correspond to a negatively charged complex defect O Si −1 , consisting of a pseudotetrahedron of 3 silicon and 1 oxygen in two slightly different environments. For PL, we attributed two bands (P0 and P1) to transitions involving O Si once again; P2 and P3 were attributed to transitions involving another complex defect [O i S i ], an interstitial silicon in close proximity to an interstitial oxygen. The existence of these defects rationalizes previous reports in the literature, in particular the increased photoresponse upon hydrogen passivation.