  Efficient electroluminescence of silicon light emitting p-n diodes with
different sizes and shapes is investigated at room temperature. High quantum
efficiency of the diodes, a long linear dependence of the electroluminescence
intensity on the diode current and a low energy shift of the emission line in
electroluminescence spectra with increasing diode current are explained by the
self-compression of injected electron-hole plasma into dense electron-hole
plasma drops. Experiments on space scanning of the electroluminescence
intensity of the diodes support this conclusion. The plasma self-compression is
explained by existence of an attraction in electron-hole plasma, compensating
the plasma pressure. A decrease of the semiconductor energy gap due to a local
lattice overheating, produced by the plasma, and the exchange-correlation
interaction could contribute to this attraction. The self-focusing of the
injection current can accompany the plasma self-compression.
