Direct evidence of quantum confinement from the size dependence of the photoluminescence of silicon quantum wires

The recent success of bulk synthesis of pure nanoscale silicon quantum wires (SiQW's) enables us to evaluate their photoluminescence (PL) characteristics under ultraviolet photoexcitation. Intensive multiple light emissions ranging from dark red to blue regions were revealed for as-grown and partially oxidized SiQW samples. The red light emission was ascribed to a quantum confinement effect originating from the crystalline core of the SiQW's that is closely mediated by the interface. However, the PL emission from green to blue is found to be definitely unrelated to quantum confinement; instead they are attributed to the radiative recombination from defect centers in the overcoating layer of the amorphous silicon oxide outside the SiQW's.