Visible Light Irradiation Effects on STM Observations of Hydrogenated Amorphous Silicon Surfaces

Abstract

Scanning tunneling microscopy (STM) observations are performed on intrinsic hydrogenated amorphous silicon (a-Si:H) surfaces under monochromatic visible light irradiation. Tunneling spectroscopy results show rectifying behavior in the dark, and tunneling current increases dramatically at a negative (reverse) sample bias when the surface is continuously exposed to monochromatic visible light. It is elucidated that the increase of tunneling current under the irradiation is caused by the photoexcited electrons, which leads to the appearance of a larger voltage across the vacuum between the probe apex and the a-Si:H surface than that in the dark. A high tunneling current under the irradiation enables us to perform stable STM observations of the intrinsic a-Si:H surface. The current image at a negative sample bias under the irradiation was different from the topographic one at a positive sample bias, which may indicate that topographic images of a-Si:H surfaces reflect not only surface electronic structures but also subsurface information determined by the growth process of a-Si:H films.