Crystal growth of polycrystalline silicon thin films for solar cells evaluated by scanning probe microscopy

We have studied the crystalline growth of photovoltaic-device-grade undoped polycrystalline Si (poly-Si) thin films produced by very high frequency (VHF) plasma enhanced chemical vapor deposition (PECVD) using a conductive scanning probe microscope (SPM) technique. Surface morphology and local current images are simultaneously measured for the poly-Si layers with a thickness, d, in the range of 0.5–5 μm. The week correlation between the topological height and the current maximum is observed for the samples with d⩾2 μm. On the other hand, the average current increases by two orders of the magnitude with increasing d from 0.5 to 3 μm. The increase in the crystalline fraction in the initial growth region just adjacent to the substrate after the deposition of the 0.5-μm-thick layer is a possible mechanism for the significant current increase.