Scanning tunneling microscopy/spectroscopy observation of intrinsic hydrogenated amorphous silicon surface under light irradiation

Continuous visible light irradiation is used to observe intrinsic hydrogenated amorphous silicon (a-Si:H) surfaces by scanning tunneling microscopy (STM) and scanning tunneling spectroscopy (STS). A deposited a-Si:H surface is wet-cleaned in order to terminate the a-Si:H surface with H atoms. A current-sample bias (I–V) curve shows a rectifying behavior in the dark, and the tunneling current increases dramatically only under the reverse-bias condition with light irradiation. This is attributed to the photoexcited minority carriers that lead to the appearance of a higher voltage across the vacuum than that in the dark. Experiments with both p-type and n-type substrates justify the suggested model. High tunneling current under irradiation enables us to obtain highly resolved STM images. Current imaging tunneling spectroscopy observations show that the detected tunneling current in the reverse direction is increased over the entire surface with irradiation, and the increment of the tunneling current is different at each surface site.