Electron Escape from Filled Band in Wet Porous Silicon Nanostructure Probed by Luminescence Quenching Dynamics

Abstract

The recovery of the photoluminescence (PL) of p-type porous silicon (PSi), after its quenching by electron injected from the substrate, was investigated. Electrons were photo-generated in the space-charge-region of the biased substrate, and then forced into PSi. The PL was quenched as a result of fast Auger recombinations. After ending electron injection the PL recovered as electrons escaped from PSi back into the substrate by tunnelling through an energy barrier at the interface. The barrier was tuned by growing an oxide in PSi. The higher the injection level, or the less transparent the energy barrier, the slower the PL recovery. The PL recovery was energy selective, the higher energy part of the spectrum recovering earlier then the lower energy part, in agreement with a band emptying itself from the top down. Under high electron injection condition, the selectivity becomes less pronounced. A simple model was proposed to confirm the origin of the PL quenching and the electron escape process by tunnelling. In some cases, it took ∼10 min or more for the PL to fully recover, showing that electrons can stay in PSi for long periods of time without recombining.