Origin of the 745 nm photoluminescence from small diameter silicon nanowires

A broad photoluminescence band centered at 745 nm was observed from Si nanowires (SiNWs) smaller than 4 nm in diameter with an oxide sheath. This emission band mainly originates from SiNWs grown along the [111] direction and its intensity increases with decreasing diameter and larger length. It becomes unobservable when the crystalline core of the SiNW is completely oxidized. Our theoretical calculations reveal electronic states in the band gap of the small diameter SiNWs when Si-O bands are formed and the results agree with experiments. This result provides insight into the electronic states of small-diameter SiNWs with surface oxide.