Effects of laser parameters on optoelectronic properties of polycrystalline silicon films prepared by two-step annealing process

Abstract

A two-step method combining furnace and laser annealing is proposed for improving the electrical and optical properties of amorphous silicon thin films on glass substrates. It is shown that the optical transmittance of the as-deposited silicon film increases from 27 to 31% following furnace annealing at 600 °C. However, the electrical resistance is too high to be measured using a four-point probe. The sheet resistance can be reduced to 270 kΩ/□ by annealing the as-deposited film using an ultra-violet (UV) laser. However, the resistance is still too high for TFT applications. The as-deposited silicon film is first furnace annealed at 600 °C for 12 h and then annealed using a UV laser with a laser power of 41 mW and a scanning speed of 60 mm/s. The optical transmittance and sheet resistance of the annealed film are found to be 29% and 1.17 kΩ/□, respectively. The X-ray diffraction (XRD) results suggest that the improved optical and electrical properties are the result of an amorphous-to-crystalline transformation of the silicon microstructure.