Selective charge injection induced microstructural modifications in hydrogenated nanocrystalline silicon: A current-sensing atomic force microscopy study

Abstract

Hydrogenated nanocrystalline silicon (nc-Si:H) films prepared by RF sputtering were studied by current sensing atomic force microscope (CSAFM) using conductive cantilevers. The tip of CSAFM was used to inject charges into the selective areas of the film at positive and negative 10 V bias. The changes in the topography and electrical conductivity of these regions were measured using contact-mode atomic force microscopy (AFM) and CSAFM. Significant changes in the surface topography and electrical conductivity were observed with charge injection. The average height of the charge injected area increased over non-injected surface, and the increase in the surface height was proportional to imaging duration. Topographical features at smaller scale, such as heights of individual grains, decreased with imaging. The changes in the topographical features are independent of bias polarity. The charge injection resulted in a large drop in local electrical conductivity, with over 95 % decrease in injected current after 36 minutes of injection. It is speculated that high energy (10 eV) charge injection resulted in breaking of local chemical bonds, increasing local free volume and creating additional mid-gap defect states. The changes in topography and electrical conductivity are attributed to these changes respectively.