## 4 Results and Discussions  
### Material and Crystal Properties  
The impact of thermal annealing temperature on the crystallization ratio of the fabricated films was studied by Raman spectroscopy in the first step of characterization process. Figure 2 shows the normalized results of Raman peak shift due to annealing temperature variation from 450 to 900 \({}^{\circ}\)C. The Raman peak of C-Si, located at 520 cm\({}^{-1}\), is also shown as the reference. The Raman spectra of the samples annealed at 450 to 550 \({}^{\circ}\)C showed a broad peak at around 520 cm\({}^{-1}\) with high levels of intensity offset for wavenumbers lower than 480 cm\({}^{-1}\) and higher than 530 cm\({}^{-1}\), which means that a large portion of the fabricated films are not crystallized under these annealing conditions, but that part of the a-Si layer is converted into nano-Si and/or micro-Si. With raising the annealing temperature to 700-750 \({}^{\circ}\)C, narrower peaks appeared closer to 520 cm\({}^{-1}\). However, the intensity offset of the measured spectra was still much higher than that of C-Si in the entire off-peak range. The existence of this offset implies that a considerable part of the film was not fully crystallized, and was probably composed of a mixture of a-Si and nano- and micro-Si. Finally, when another sample was annealed at 900 \({}^{\circ}\)C, a very narrow peak at 518.8 cm\({}^{-1}\) was detected, but even at this high temperature, a small peak was observed at around 500 cm\({}^{-1}\) (as shown by a dashed oval in Figure 4a) which confirmed that the crystallization process had not run to completion. To calculate the crystallized volume fraction of the annealed samples, we used Equation (1), which determines the crystallization ratio (\(R_{x}\)) based on the Raman spectra intensity of different phases of Si crystallization in the thin film layers. \[R_{x}=\frac{I_{c}+I_{m}}{I_{c}+I_{m}+0.85\times I_{a}} \tag{1}\]  
In this equation, \(I_{a}\) and \(I_{c}\) are the intensity of Raman spectra at 480 cm\({}^{-1}\) and 520 cm\({}^{-1}\), which correspond to the a-Si and C-Si phases, respectively, while \(I_{m}\) is the average intensity of Raman spectra from 494 to 507 cm\({}^{-1}\), which represents the intensity of the mixture of a-, nano- and micro-Si phases [29]. As shown in the graph of Figure 3, for annealing temperatures lower than 800 \({}^{\circ}\)C, which is the eutectic point of a Si-Cu binary alloy system, \(R_{x}\) was less than 80%. More precisely, we reached a crystallization ratio of \(R_{x}\approx 77\%\) at 775 \({}^{\circ}\)C, which is in accordance with the result of a similar experiment carried out  
Figure 4: (**a**) Normalized Raman spectra of the CuLC micro-Si films fabricated on a glass substrate after thermal annealing at various temperatures, (**b**) The crystalized volume fraction of the fabricated CuLC micro-Si films vs. annealing temperatures. in [30]. The highest values, i.e., \(R_{x}\) was 93.6%, were calculated from the Raman spectra of the sample annealed at 900 \({}^{\circ}\)C.  
In the second step of the characterization process, we investigated the crystal orientation and calculated the grain size of the CuIC micro-Si films by XRD spectroscopy. The results of four samples annealed at 550, 650, 750 and 950 \({}^{\circ}\)C are shown in Figure 5. The micro-Si crystals in the sample annealed at 550 \({}^{\circ}\)C were not dominant in any orientation, except for a very small peak in the \(<\)220\(>\) plane. After annealing the thin film samples at higher temperatures, i.e., 650 \({}^{\circ}\)C and 750 \({}^{\circ}\)C, three peaks, i.e., Si \(<\)111\(>\), \(<\)220\(>\) and \(<\)311\(>\), appeared in the XRD spectra. It was observed that the Si \(<\)111\(>\) peak was stronger than the \(<\)220\(>\) and \(<\)311\(>\) peaks, which supports the explanations given in [31].