Photoluminescence mechanism for blue-light-emitting porous silicon

A comparative study of photoluminescence (PL) and photoluminescence excitation (PLE) spectra of porous silicon (PS) and Si oxide, both enlitting blue light, is reported. The PLE spectrum of Si oxide monitored at 160 nm displays a three-peak structure with peak wavelengths around 265, 300, and 360 nm. The PLE intensity of the PS sample increases with decreasing excitation wavelength, and has three shoulders located at wavelengths near the three PLE peak wavelengths of Si oxide. When the PS sample is oxidized for half an hour at 1150C [the temperature at which nanometer Si particles (NSP's) inside PS disappear], blue-light PL intensity reduces greatly, and its PLE spectrum changes into a spectrum very similar to that of Si oxide. The experimental result strongly indicates that for the blue-light emission from PS there are two types of photosxcitation processes: photoexcitation occurs in NSP's and in the Si oxide layers covering NSP's, and radiative recombinntion of electron-hole pairs is carried out in luminescence centers located on the interfaces between NSP's and Si oxide and in those inside Si oxide layers.