Femtosecond laser induced surface nanostructuring and simultaneous crystallization of amorphous thin silicon film

X. C. Wang,H. Y. Yu,K. L. Pey,C. W. Tan,H. Y. Zheng,F. Wang

doi:10.1364/oe.18.019379

Abstract

Ultrafast pulsed laser irradiation is demonstrated to be able to produce surface nano-structuring and simultaneous crystallization of amorphous silicon thin film in one step laser processing. After fs laser irradiation on 80 nm-thick a-Si deposited on Corning 1737 glass substrate, the color change from light yellow to dark brown was observed on the sample surface. AFM images show that the surface nano-spike pattern was produced on amorphous-Si:H film by fs laser irradiation. Furthermore, micro-Raman results indicate that the a-Si has been crystallized into nanocrystalline Si. Also, the absorptance of the fs laser treated Si thin film was found to increase in the spectrum range of below bandgap compared to original untreated a-Si. The developed process has a potential application in fabrication of high efficiency Si thin film solar cells.

Highlights

Hydrogenated amorphous silicon (a-Si:H) is one of the most widely used material for photovoltaics application due to its low fabrication cost compared to their crystalline counterpart because of its high deposition rate, low deposition temperature, which can enable the usage of inexpensive substrates such as glass, plastic and metal foils
We demonstrated that infrared femtosecond laser is able to induce crystallization of amorphous silicon and simultaneous surface nanostructuring on a-Si:H surface in one step process
It can be clearly seen that after laser irradiation the a-Si film was turned into dark brown from original shinny light yellow color, which indicates the surface property such as surface finish, and phase state might change after laser treatment

Summary

Introduction

Hydrogenated amorphous silicon (a-Si:H) is one of the most widely used material for photovoltaics application due to its low fabrication cost compared to their crystalline counterpart because of its high deposition rate, low deposition temperature, which can enable the usage of inexpensive substrates such as glass, plastic and metal foils. Unlike excimer laser annealing process, ultrafast pulsed laser interaction with a-Si thin film material involves nonlinear photoenergy absorption and nonequilibrium thermodynamics that are expected to dominate the interaction [9,10,11]. Such a nonlinear process provides precise and low-threshold fluence associated with femtosecond laser ablation [6,11,12]. We demonstrated that infrared femtosecond laser is able to induce crystallization of amorphous silicon and simultaneous surface nanostructuring on a-Si:H surface in one step process. The developed process has potential application for fabrication of high efficiency Si thin film solar cells, thin film transistor (TFT) for AMLCD application, and other novel optoelectronic devices

Experimental

Results and discussion

Conclusions