Electroluminescence and nature of lightly spark-processed silicon
We report the emission of significant infra-red as well as visible electroluminescence (EL) from lightly spark-processed Si (LSP-Si). Studies by scanning tunnelling microscopy (STM) reveal the presence of small globules down to around 2 nm in diameter, the sizes necessary for significant quantum confinement and blue-shifted interband radiation to occur. However, studies with oxidized samples and samples processed in non-oxygen gases suggest that silicon oxides play a major role. Measurements by elastic recoil detection analysis and Rutherford back scattering analysis show that LSP-Si has a 150-250 nm thick oxidized surface layer. This layer is some four times thicker in medium sparked samples. There is negligible foreign material other than oxygen and slight C and N. Samples without encapsulation show changes in resistance but no change in efficiency after 500 hours of pulse operation.