Luminescence due to electron-hole condensation in silicon-on-insulator

We show that photoluminescence from a thin silicon-on-insulator (SOI) layer with a thickness of about 0.1 mu m excited by ultraviolet (UV) light originates from the recombination of electrons and holes in their condensed phase. The UV excitation increases the density of electrons and holes in the SOI layer, since the UV light is predominantly absorbed in that layer and the excited carriers cannot diffuse into the base wafer because of the presence of a buried oxide layer which acts as a diffusion barrier. As a result, a characteristic "condensate luminescence" is emitted from the SOI layer. The spectral shape of the condensate luminescence agrees with the calculated shape using convolution of the occupied electron and hole densities of states. A systematic spectral change induced by the variation of excitation intensity and the sample temperature is consistently explained by the phase diagram of the electron-hale system in Si which consists of free exciton (FE), electron-hole plasma (EHP), and electron-hole liquid (EHL). The phase transition from FE to EHP or that from FE to EHL is observed with increasing excitation intensity, according to whether the temperature is higher or lower than the critical temperature of EHL. These results confirm for us that the condensate luminescence in the SOI layer is due to the recombination of electrons and holes in their condensed phase. (C) 1998 American Institute of Physics. [S0021-8979(98)02116-1].