Transport and structural properties of silicon films in the amorphous-to-microcrystalline transition region

Abstract

Undoped hydrogenated microcrystalline silicon (μc-Si:H) thin films have been deposited by plasma enhanced chemical vapor deposition (PECVD) at low temperature with different hydrogen dilutions and rf powers. Large complexity of microstructure in hydrogenated microcrystalline silicon and the existence of different sizes of crystallites are demonstrated by different characterizations. The authors correlate the transport properties with the structural properties of the rf PECVD grown μc-Si:H in the amorphous-to-crystalline transition region. For chamber pressure of 2.0Torr and rf power density of 310mW∕cm2, the onset of crystallinity is observed for the film deposited at a hydrogen dilution of 94%. At a hydrogen dilution of 95%, amorphous-to-microcrystalline transition have been observed. This film exhibits a dark conductivity of 2.7×10−7Scm−1 and a crystalline volume fraction of 21%. The mobility-lifetime product for these films are 3.8×10−6cm2∕V and hole diffusion length is 70nm. Fourier transform infrared study shows mainly monohydride bonding in this film. This film becomes stable after 30h of light soaking.