Exposure to ammonia (NH_3) increase the dark current (DC) in porous silicon (PS),but evaporated selenium (Se) deposited on PS decreases DC.Photoluminescence (PL) measurement shows that there are two types of centers.PL in one region of PS (Peak approx 800nm) initially increases with the NH_3 exposure and then decreases.But the PL from another region of PS has a peak at approx 780nm and it decreases continuously with the NH_3 exposure.Dipping PS in water and drying in air shifts the PL peak at 800 nm to 744 nm.Atomic force Microscopy (AFM) shows that the as prepared sample has views of diameters 2.4 nm,3.4nm,4.6nm and bigger.However,in the AFM images of the water treated sample the wires of diameter 3.4nm and 4.6nm are absent.The PL results are explained using the AFM data and the John-Singh model of quantum confinement.
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