TIME-VARYING PHENOMENA IN THE PHOTOELECTRIC PROPERTIES OF POROUS SILICON

We have undertaken a systematic study of porous silicon with the use o f photoconductivity and photoluminescence. During this, we have observ ed at least three kinds of time-varying photoconductivity, of which tw o reduce the conductivity and one increases the conductivity during il lumination. In addition, we have observed persistent photoconductivity . The time developments of the photoconductivity as well as the persis tent photoconductivity depend in intricate ways on parameters such as the wavelength and intensity of the illuminating light, the potential drop across the sample, the surface treatment, and the dark current va lue. The time scale of these time-varying effects ranges from a few mi nutes to several hours. The results are discussed in terms of the phot oelectric properties of the supporting silicon wafer, diffusion of hyd rogen, and photoinduced desorption of hydrogen. (C) 1997 American Inst itute of Physics.