Time-resolved photoluminescence measurements in spark-processed blue and green emitting silicon

Time-resolved photoluminescence (PL) measurements on spark-processed Si (sp-Si) are compared with those on dry-oxidized porous Si (p-Si). Both types of substances yield non-exponential decay times in the nanosecond region which are essentially independent of the detection wavelength. However, subtle differences between photoluminescing sp-Si and oxidized p-Si exist. Specifically, blue/violet emitting sp-Si has a peak wavelength near 410 nm (3eV) under steady state conditions whereas oxidized p-Si luminesces with a maximum centred around 460-480 nm (2.7 - 2.58eV). Further differences include the peak structures in the PL spectra, the decay dynamics, and certain features in the lifetime distribution. It is concluded from the data that sp-Si and p-Si derive their PL from somewhat different mechanisms. Moreover, differences in decay times between SiO₂ and sp-Si suggest that silica does not seem to be the major cause for PL in sp-Si.