Photoluminescence Due to Degenerate Electron-Hole System in Silicon-on-Insulator Wafers under Ultraviolet Light Excitation

Photoluminescence (PL) spectroscopy has been used for characterization of silicon-on-insulator (SOI) wafers with SOI thickness of 75 nm fabricated by separation by implanted oxygen (SIMOX) technique. While PL signals from the substrate were dominant under conventional visible light excitation, a characteristic broad line was observed under ultraviolet (UV) light excitation throughout our temperature range between 4.2 to 70 K. The spectral distribution of the characteristic line agreed with calculated shape using convolution of the occupied electron and hole densities of states. This agreement can be regarded as strong evidence for formation of degenerate electron-hole systems, electron-hole liquid and electron-hole plasma, in the SOI layer. The detection of luminescence due to these systems allows us to suggest that relief of crystalline damage in the SOI layer induced by oxygen implantation and improvement of quality of interfaces between the SOI layer and oxide layers are efficiently achieved in the present low dose SIMOX process with an internal thermal oxidation.