Deep-level luminescence in Czochralski-grown silicon crystals after long-term annealing at 450 degrees C

Isothermal annealing at 450 degrees C for more than 100 h was performed for Czochralski-grown silicon crystals. We detected a photoluminescence (PL) band at around 0.86 eV at room temperature. Temperature dependence of PL spectra indicates that the 0.86 eV band has an origin distinct from that of the 0.885 eV line observed at liquid helium temperature. Spectral shape analysis using the curve-fitting technique indicates that at least two different electronic levels are formed by oxygen precipitation during annealing. The peak energy position and half-width of the 0.86 eV band were different from those of a similar 0.86 eV band resulting from two-step annealing al 450 degrees C and subsequently at 650 degrees C. The difference in the spectral shape is ascribed to the structural change of oxygen aggregates. We believe that PL at room temperature is sensitive to the morphology of these aggregates.