A model for the electroluminescence of spark-processed Si Original Research Article

We have fabricated electroluminescent (EL) devices from spark-processed Si (sp-Si) using n and p-type silicon. Visible light emission with peaks at around 650 and 730 nm was obtained from devices fabricated using Ag, Au and Al as semitransparent contacts through which the light is emitted. EL is observed under the condition of electron injection into the sp-Si layer for both n and p-type silicon. These devices displayed quasi-rectifying current–voltage (I–V) characteristics. Devices fabricated using indium–tin-oxide (ITO) as the semitransparent contact displayed ohmic device characteristics and no light emission was observed. A study of the dependence of the threshold voltage for EL (and EL intensity) on wafer resistivity for n-type Si did not reveal a behavior consistent with carrier inversion, necessary if an injection mechanism were responsible for the luminescence. Absorption peaks were measured in the same spectral range as the emission peaks, and the changes in EL intensity with pre-metallization annealing temperature correlated with the changes of defect concentrations with annealing temperature in sp-Si. It is proposed that electrons generated by impact ionization relax to the ground state via luminescing centers present in sp-silicon resulting in the observed light emission. The dependence of the reverse bias current on temperature for sp-Si EL devices was found to be consistent with impact ionization.