Colour-switching effect of photoluminescent silicon after spark-processing in oxygen

Abstract

We report on a new colour-switching effect of photoluminescing spark-processed silicon which was prepared in pure oxygen. Whereas as-prepared specimens display an orange PL peaking at 655 nm (1.89 eV), the PL changes to a more intense blue emission centred at 475 nm (2.61 eV) when the sample is subjected to a lower pressure. The same blue PL band is observed after heat treatments up to . Moreover, at annealing temperatures above a third radiative transition emerges in the infrared and eventually dominates the spectrum. A model is suggested that links ozone molecules, generated during spark-processing and incorporated into the sp-matrix, to the orange PL band. The results of heat treatments and temperature-dependent PL measurements allow for the relationship of the 2.61 eV band to oxygen deficiency centres, created by out-driven ozone molecules. The IR band is discussed in the light of luminescing properties of porous silicon and silicon oxides. The experiments demonstrate that the UV/blue (3.25 eV) and green (2.36 eV) PL bands for Si spark-processed in air cannot be related to radiative transitions in silicon oxides.