COLOR-SWITCHING EFFECT OF PHOTOLUMINESCENT SILICON AFTER SPARK-PROCESSING IN OXYGEN

We report on a new colour-switching effect of photoluminescing spark-p rocessed silicon which was prepared in pure oxygen. Whereas as-prepare d specimens display an orange PL peaking at 655 nm (1.89 eV), the PL c hanges to a more intense blue emission centred at 475 nm (2.61 eV) whe n the sample is subjected to a lower pressure. The same blue PL band i s observed after heat treatments up to 350 degrees C. Moreover, at ann ealing temperatures above 400 degrees C a third radiative transition e merges in the infrared and eventually dominates the spectrum. A model is suggested that links ozone molecules, generated during spark-proces sing and incorporated into the sp-matrix, to the orange PL band. The r esults of heat treatments and temperature-dependent Pt measurements al low for the relationship of the 2.61 eV band to oxygen deficiency cent res, created by out-driven ozone molecules. The IR band is discussed i n the light of luminescing properties of porous silicon and silicon ox ides. 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.