## 4 Results and Discussions
### Material and Crystal Properties
When we annealed the sample at a much higher temperature, i.e., 950 \({}^{\circ}\)C, the corresponding Si \(<\)111\(>\) peak got narrower and stronger, which indicates that the crystal growth in the \(<\)111\(>\) direction is dominant and with a higher preference. However, at the same time, the peaks of \(<\)220\(>\) and \(<\)311\(>\) become narrower and stronger, so the relative intensity of \(I_{<\)111\(>\)/(\(I_{<\)220\(>}+I_{<\)311\(>}\)) reduced from 1.175 to 1.08. This means that increased thermal treatment has a negative impact on the fabricated film properties, because it increases crystal growth in undesirable orientations and can reduce the uniformity and quality of the resulting microcrystal layer. To determine the grain size of the micro-Si in \(<\)111\(>\) direction, we used the Scherrer equation which is introduced in Equation (2), wherein \(\lambda\) is the wavelength of the scanning X-ray, \(\theta\) is the half angle of diffraction peaks and \(B\) is the half width of diffraction peak (in radians). The crystal grain sizes can be calculated from the full width at half the maximum (FWHM) value of the micro-Si thin film peak [29]. The result of the calculated grain size is shown in Figure 5b. The largest calculated grain size of the CuIC micro-Si thin films in \(<\)111\(>\) orientation was almost 20 nm. In addition, it was observed that for annealing temperatures lower than Si-Cu eutectic point, smaller grain sizes occurred. \[D=\frac{0.89\lambda}{B\cos\theta} \tag{2}\]  
Following the XRD measurements, the surface of the micro-Si thin film deposited on glass substrates (i.e., glass/p-Si/Cu samples) was studied using optical microscopy. Figure 6 shows three images, taken at three zoom levels, of the samples which was annealed at 550 \({}^{\circ}\)C. These optical micrographs reveal interesting details about the nucleation of the Si atoms, and the beginning of the  
Figure 5: (a) XRD spectra of CuIC p-type micro-Si thin films fabricated on a quartz glass substrate. Note: the 2 nd, 3 rd and 4 th XRD spectra are shifted by 10\({}^{\circ}\), 20\({}^{\circ}\) and 30\({}^{\circ}\), and by 2500, 5000 and 7500 units on the horizontal and vertical axes, respectively, for more clarity, (b): the calculated grain size of the CuIC micro-Si films formed in \(<\)111\(>\) plane vs. annealing temperature. formation of a micro-Si layer due to the heat treatment. The left micrograph in Figure 6 shows the overall texture of the fabricated film, which is obviously neither uniform nor continuous. However, several regions may be distinguished as crystallization areas. The middle image shows more detail of the micro-Si film morphology of one of these areas, which contains some bulks of residual copper on the film surface after the thermal treatments. This leftover metal can reduce the light absorption efficiency in PV applications. A closer look at the surface of this sample shows there are many small pink spots (indicated by arrows (a)) on the film surface which are likely clusters of nano-Si nucleation centers that individually formed shortly after the beginning of annealing treatment at 550 \({}^{\circ}\)C. These clusters expanded and coalesced into each other as the annealing process progressed. According to Figure 6, several areas with dendrite shapes (indicated by contours (b)) formed and grew, leading to further lateral expansion and the creation of larger grain boundaries. There are also some dark spots on the film surface which could be small clusters of residual Cu after the thermal annealing step in the CuIC process. When we annealed another sample at 750 \({}^{\circ}\)C, we observed quite different crystallization conditions, as shown in Figure 7. The major part of the film surface was covered by a bright beige continuous layer, which may be seen in the background of this figure. According to the measured Raman spectra, we think that this area is mainly in the micro-Si phase. Firstly, much larger crystallized areas were observed on the film surface, which formed a bright beige, almost continuous layer.