Electroluminescence and nature of lightly spark-processed silicon

Abstract

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.

Electroluminescence from mechanically damaged oxidized silicon

“…In the case of lightly SP-Si, our recent studies 12 indicate that the spectrum of EL is similar to that in Fig. 5, with a peak at above 650 nm, together with stronger infrared radiation peaked at the Si band gap.…”

“…10 In the cases of por-Si ͑Ref. 12͒ and SP-Si, 12 there is evidence for the presence of nanoparticles, so that quantum-confinement hypotheses for explaining both the blueshift and the enhanced emission intensity are possible.…”

Visible electroluminescence from native SiO2 on n-type Si substrates

“…6 This visible EL is also similar to that from lightly spark processed Si, mechanically damaged SiO 2 /Si, and laser-grooved Si. [10][11][12] Similar experiments on a p-type sample with native oxide gave similar emission, but EL only occurred under forward biased conditions. This is to say that in p and n cases, for visible EL to occur, the top metal electrode must be negatively biased, i.e., electrons must be injected into the Si wafer from the metal electrode.…”

Improved electroluminescence of spark-processed silicon by an aerosol-assisted technique

“…Other investigators [2] using conventional sp found EL spectra, which appear to peak near 950 nm (1.31 eV), 775 nm (1.6 eV) and 650 nm (1.9 eV) when utilizing a few selected optical filters instead of a continuous spectrometer, as we did. In a later paper the same investigators [4] moved the 950 nm peak to 1150 nm (1.1 eV) .…”