It is demonstrated that there are distinct off and on states in the current-voltage characteristics of porous silicon ͑PS͒ diodes, and that the visible electroluminescence ͑EL͒ is observed in the on state. The PS diodes are composed of semitransparent thin Au films, rapid thermal oxidization ͑RTO͒-treated PS layers ͑ϳ0.5 m thick͒, p-type Si substrates, and ohmic back contacts. After the PS layers were prepared by anodizing Si wafers in an ethanoic HF solution, the samples were treated by RTO

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... cess. The bistable states of this PS diode can be simply and reversibly controlled by the external bias voltage. Based on the behavior of the EL and capacitance-voltage characteristics, the model of memory effect is presented, in which field-induced carrier injection and ejection into and from silicon nanocrystallites strongly affects the carrier transport.