Luminescence due to electron-hole condensation in silicon-on-insulator and its application to defect and interface characterization

Photoluminescence of silicon-on-insulator (SOI) wafers was investigated using ultraviolet (UV) light as an excitation source. A characteristic emission band appeared at liquid helium temperature with a shape similar to the electron-hole liquid signal. The band was observable over a wide temperature range up to room temperature with systematic peak shift and broadening. The spectral shape analysis of the band indicates that the emission occurs as a result of the recombination of photoexcited electrons and holes in their condensed phase. The condensation is realized, since UV light is absorbed predominantly in the SOI layer and the SOI structure prevents the photoexcited carriers from diffusing into the substrate. This was confirmed by the spectral dependence on the excitation intensity and the SOI layer thickness. We showed that the characteristic emission is sensitive to the microdefects and the interfacial quality, suggesting its applicability to the characterization of SOI wafers.