Photoluminescence Recovery after its Quenching by Carrier Injection in Partially Oxidized Porous Silicon

摘要

Recently, we have shown how photoconduction can be used to monitor the evolution of porous silicon(PSi) in HF solutions (dissolution; photo-dissolution) . The principle is based on the photocurrentbeing a signature of light transmission through PSi and thus probing changes in optical absorption. Here,we use the photoconduction technique to study the electrochemical oxidation (ECO) of p-type PSi and thephenomenon of photoluminescence (PL) quenching triggered by electron injection from the substrate. Wefocus on (ⅰ) quantum confinement effects during ECO and (ⅱ) PL recovery after stopping electron injection.(ⅰ) was successfully shown in the photocurrent evolution obtained with different light sources, confirmingthat ECO proceeds by oxidizing selectively first large nanocrystallites and later on smaller ones. For (ⅱ),the effect of oxide level, emission energy, level of electron injection and electric polarization were studied.In our experiments, electron injection was performed by reverse biasing the p-type PSi/Substratejunction under illumination at 670 nm. This light was mainly absorbed in the substrate and not much in PSi.Then, electron-hole pairs generated in the space-charge-region were separated by the electric field there andelectrons could penetrate into PSi and trigger PL quenching by Auger mechanism [3]. After stoppingillumination and voltage application, the PL recovery was monitored as a function of time. The recoverytime was quite short for non-oxidized PSi but became longer as the oxide level was increased, reachingminutes in some cases, as shown in Fig. 1. At an oxide level where the electrical contact between thesubstrate and PSi was broken, no electron injection could be achieved and no PL quenching could beobserved.