OBSERVATION OF TIME-VARYING PHOTOCONDUCTIVITY AND PERSISTENT PHOTOCONDUCTIVITY IN POROUS SILICON

We have observed time-varying photoconductivity and persistent photoco nductivity in porous silicon, both with time-evolution scales of the o rder of several minutes or hours. The time evolutions depend on the wa velength and the intensity of the illuminating light. The data indicat e the presence of at least two competing mechanisms, one is tentativel y related to photoinduced creation of charge carriers in the silicon s ubstrate followed by diffusion into the porous silicon layer, and the other is tentatively related to desorption of hydrogen from the porous silicon. (C) 1996 American Institute of Physics.