Properties of electric transport in crystallized silicon films under different annealing temperatures

Abstract

Hydrogenated amorphous Si thin films were prepared by plasma-enhanced chemical vapor deposition. As-deposited samples were annealed at different temperatures to obtain nano-crystalline Si. During the transition process from amorphous to nano-crystalline structure, Raman scattering spectroscopy was used to characterize the changes of microstructures. The temperature-dependent conductivity was measured in order to understand the electric transport processes in the films. It was found that the crystallization occurs at around 700 °C. The crystal volume fraction （Xc） increases with the increase of annealing temperature, and in the case of the Si film annealed at 1000 ℃, the Xc is beyond 90%. The carrier transport characteristics in the films annealed at the different temperatures are different from the as-deposited film. For the sample annealed at 700 ℃, the carrier transport is strongly influenced by the defect states resulting from the effusion of hydrogen, and it is controlled by the hopping conduction of the localized states in the difference measurement temperature regions causing the dual activation energies. For the highly crystallized Si film annealed at 1000 °C, the transport process is strongly influenced by the transport of the extended states in the crystalline silicon, while in the high temperature region, the quantum tunneling process plays an important role in the carrier transport property.