Numerical and experimental analysis on green laser crystallization of amorphous silicon thin films

Abstract

The effect of laser fluence on the crystallization of amorphous silicon irradiated by a frequency-doubled Nd:YAG laser is studied both theoretically and experimentally. An effective numerical model is set up to predict the melting threshold and the optimized laser fluence for the crystallization of 200-nm-thick amorphous silicon. The variation of the temperature distribution with time and the melt depth is analyzed. Besides the model, the Raman spectra of thin films treated with different fluences are measured to confirm the phase transition and to determine the optimized fluence. The calculating results accord well with those obtained from the experimental data in this research.

Variation of optical parameters of multilayer structures with thin silicon layers at laser annealing

“…One can see that, contrary to the quartz/Si structures, the RS spectra of initial glass/Si structures have two bands, ~480 and ~520 cm -1 . This indicates that a silicon film on glass has inhomogeneous phase composition and involves both -Si and poly-Si phases [1,4]. Similarly to the case of the quartz/Si structures, a small decrease of the ~520 cm -1 band halfwidth and a decrease of the ~480 cm -1 band intensity are observed in the glass/Si structures as the laser radiation power grows.…”

“…3, curves 2 and 3) [11]. One can see that the RS spectra of the initial specimen have a broad band in the region of 480 cm -1 that is related to -Si [1,4]. After laser annealing, a band ~520 cm -1 appears in the RS spectrum of the quartz/Si structure.…”

“…After laser annealing, a band ~520 cm -1 appears in the RS spectrum of the quartz/Si structure. According to [1,4], it is related to light scattering from TO phonons in silicon nanocrystallites and is due to the quantum confinement effect that is a sign of phase transition from -Si to nano-Si. As the laser radiation power is increased, the half-width of RS peak in the region of ~520 cm -1 goes down and the peak form becomes more symmetric.…”

“…It enables to modify certain micro-areas without affecting neighboring sections and lower layers. Application of laser annealing makes it possible to prepare polycrystalline silicon (polySi) films which is promising for use in thin-film transistors, liquid-crystal displays, sensors and solar cells because of recrystallization of amorphous Si (-Si) films [1]. Besides, laser annealing enables to modify electrophysical and optical parameters of semiconductors as well as their crystalline and defect structure [2,3].…”

“…In the course of laser annealing of -Si or poly-Si layers deposited onto a single crystalline Si substrate, their homoepitaxial recrystallization occurs [1,4]. Such processes may help to obtain the most efficient presentday cascade solar cells with the structure of -Sipoly-Si structure.…”