Influence of combined AFM/current measurement on local electronic properties of silicon thin films

Hydrogenated microcrystalline silicon (μc-Si:H) thin films were prepared by plasma enhanced chemical vapour deposition (PECVD) and transferred without breaking vacuum into an ultra high vacuum (10−10 mbar) atomic force microscope (AFM). The AFM is used to characterize surface morphology and electronic properties with high lateral resolution. This combined AFM/current measurement leads to a modification of the local electronic properties. This modification is detected as a significant decrease in local current compared to that in newly scanned regions. Kelvin probe microscopy shows that the contact potential difference is reduced by 0.25 eV in the area with decreased conductivity. This area with decreased conductivity remains on the surface for at least several hours. When the cantilever is held at a particular point on the surface, the current exhibits a long-term decay (≈10 min). It is suggested that may be due to a local change of a gap state distribution.