Light-emitting silicon pn diodes

We report on the electrical and optical characteristics of silicon light-emitting pn diodes. The diodes are prepared by ion implantation of boron at high doses and subsequent hightemperature annealing. Under forward bias, the diodes emit infrared electroluminescence closely below the band gap of bulk Si. We present a rate-equation model for bound excitons, free excitons and free carriers which successfully describes the electrical and optical behaviour of the diodes at low temperatures. Especially, an electrical bistability observed below 50 K is shown to be based on the interplay of bound excitons, free excitons and free carriers in the active area of the diodes. The ionisation of bound excitons is the origin of an improved electroluminescence from the diodes at higher lattice temperatures. PACS 78.60.Fi; 78.55.Ap; 71.35.-y; 71.55.Cn