Spectroscopy and Topography of Deep-Level Luminescence in Photovoltaic Silicon

The aim of this paper is to identify the origin of a deep-level emission band with a peak at about 0.8 eV observed in photoluminescence from defective areas in multicrystalline Si crystals at room temperature. We compare the band with that in a plastically deformed float-zone and annealed Czochralski-grown Si crystals investigated in detail previously for microelectronic applications and point out the similarities in spectroscopic characteristics and in spatial distributions around dislocations. This prompted us to suggest that the 0.8-eV band consists of two dislocation-related components termed D_a1 and D_a2 at about 0.79 and 0.94 eV, respectively, and an oxygen-precipitation-related component Db at approximately 0.87 eV. Spatial variations of the three components around dislocation clusters forming small-angle grain boundaries reflect secondary defects or impurities trapped by the strain field around the dislocations, the intrinsic nature of the dislocations, and preferential oxygen precipitation on the dislocations, respectively. The presence of oxygen precipitates in a region emitting the strong Db component was confirmed by highly spatially resolved and highly sensitive secondary ion mass spectroscopy and by mapping of oxygen by luminescence activation using electron irradiation. Anisotropic properties expected for the dislocation-related D_a1 component were detected by polarized luminescence imaging.