Origin of emission from porous silicon: Temperature-dependence correlationwith proton conductivity

The excitation, emission, and Fourier transform infrared (FTIR) spectra of freshly prepared and aged porous : silicon (PS) are examined. The effects o f aging and temperature changing on the emission and excitation spectra of fresh and aged PS samples is also studied. Aging in air is found to result in a redshift in the emission spectrum, but a blueshift in the excitation s pectrum. Increasing the temperatures leads to a general decrease in the emi ssion intensities of both samples: however, the green emission of fresh sam ple shows an unusually large and sudden increase in its intensity at the sa me: temperature at which the proton conductivity in the silicon wafer incre ases. The temperature dependence of the O-H vibration intensity of silicon wafers shows a sudden decrease at that temperature. These results are consi stent with a model in which the excitation leads to the formation of excito n in the confined nanostructure, and the formation of electron and hole tha t are trapped by surface traps, whose nature is dependent on the chemical c omposition of the surface land thus;its age). These conclusions are confirm ed by the results of the FTIR spectra of the two samples, the temperature d ependence of the emission, and its correlation with the proton conductivity in the fresh PS.