Geminate and distant-pair radiative recombination in porous silicon

We have performed time-resolved measurements of porous silicon (PS) photolu minescence (PL) at temperatures in the range from 15 K to 300 K for differe nt emission energies. For the first time we have observed lifetimes of radi ative recombination ranging from nanoseconds to seconds. Strong phosphoresc ence was revealed for as-prepared samples at 15 K and also for partly oxidi zed specimens at room temperature. The PS luminescence had a polarized comp onent that was strongly dependent upon the detection energy and the prehist ory of the specimens studied. We analyse two possible scenarios of radiativ e recombination in PS: (1) migration of nonequilibrium charge carriers betw een nanometre-sized silicon clusters prior to recombination; (2) geminate r ecombination of charge carriers thermalized in the same or neighbouring sil icon domains. Combination of these scenarios allows us to explain the PL of PS on all timescales from one viewpoint. We present direct Monte Carlo sim ulations of recombination processes in PS, and show that the results are in good agreement with experimental data.