Experimental and computational investigation of microcrack behavior under combined environments in monocrystalline Si

Abstract

An investigation of microindenter-induced crack evolution with independent variation of both temperature and relative humidity has been pursued in PV-grade Si wafers. Under static tensile strain conditions, an increase in subcritical crack elongation with increasing atmospheric water content was observed. To provide further insight into the potential physical and chemical conditions at the microcrack tip, micro-Raman measurements were performed. Preliminary results confirm a spatial variation in the frequency of the primary Si vibrational resonance within the cracktip region, associated with local stress state, whose magnitude is influenced by environmental conditions during the period of applied static strain. The experimental effort was paired with molecular dynamics (MD) investigations of microcrack evolution in single-crystal Si to furnish additional insight into mechanical contributions to crack elongation. The MD results demonstrate that crack-tip energetics and associated crack elongation velocity and morphology are intimately related to the crack and applied strain orientations with respect to the principal crystallographic axes. The resulting elastic strain energy release rate and the stress-strain response of the Si under these conditions form the basis for preliminary micro-scale peridynamics (PD) simulations of microcrack development under constant applied strain. These efforts will be integrated with the experimental results to further inform the mechanisms contributing to this important degradation mode in Si-based photovoltaics.