## 3 Results and Discussion
In the case of the deposition temperature, the surface doping concentration was similar to that of the temperature increase, but the doping depth increased. In the case of the drive-in temperature, the surface doping concentration increased based on the temperature increase, and it also tended to increase proportionally. To confirm the uniformity of surface resistance after the formation of the emitter layer based on the temperature difference between the pre-deposition and drive-in processes, the average value of the sheet resistance was measured at five points of the sample after doping. In the emitter formation process, the doping uniformity was important during the electrode formation and firing. The uniformity of doping represents the uniformity of the concentration distribution and junction depth, which has a considerable effect on the generation of leakage current after the electrode formation and firing processes. As a result, we obtained a lightly doped emitter sample with an average sheet resistance and uniformity of 80.78 \(\Omega\)/sq and 4.11%, respectively. The effects of the laser fluence and scan speed (critical laser parameters) were investigated to achieve the optimal conditions for an ideal selective emitter: a sufficiently and heavily doped region and a reduction in the recombination velocity. The resulting doping level, surface melting profile, and damage to the substrate from each laser parameter were discussed. In this study, a heavily  
Figure 3: SIMS (Secondary-ion mass spectrometry) profile of the emitter layer with a temperature difference between the pre-deposition and diffusion processes. Figure 2: Lifetime of the emitter layer in relation to the temperature difference between the pre-deposition and diffusion processes. doped emitter was formed by a laser using PSG formed in a lightly doped emitter through a POCl\({}_{3}\) diffusion furnace. The spin on doping (SOD) dopant sources were used for the LDSE process, but SOD was not used in this study. Because no additional dopant was administered to silicon (Si), the laser process redistributed the dopant from the thermally diffused phosphor emitter and potentially activated the dopant from the dead layer. Sheet resistance can be significantly reduced without applying SOD. The laser intensity during the LDSE process is an important factor that can determine cell characteristics. In the heavily doped region, the sheet resistance decreased with increasing laser intensity because more dopants entered the emitter layer, and the c-Si wafer could have been destroyed if the laser intensity was excessive. Moreover, because the recombination of the carriers increased due to the surface damage, it was important to find a laser optimization condition that would minimize the laser damage and obtain a high doping concentration. The first laser parameter that was investigated was the laser fluence. The following laser parameters were used in this experiment: a 500 kHz repetition rate and a 100 mm/s laser speed. The laser power was varied from 0.8 to 5.6 W to form a heavily doped emitter. The energy density or fluence was measured in J/cm\({}^{2}\). Therefore, the fluence is mathematically defined as the integral of the power of a single beam pulse over time divided by the spot size of the beam. Because the power meter measures the average beam power over an extended period of time, as expressed by the heat generated by the laser energy, the expression for calculating the fluence can be simplified as \((\frac{P}{f})/(\pi((\frac{D}{2})^{2})\), where \(P\) is the beam power measured by a laser power meter (Watts),\(f\) is the repetition rate or pulsing frequency (Hz), and \(D\) is the beam diameter (cm) [12]. The laser fluencies corresponding to the laser power of 0.8-5.6 W were 0.3-2.25 J/cm\({}^{2}\), respectively. Figure 4 shows the graph of the sheet resistance and the amount of decrease in the sheet resistance of the emitter layer with laser fluence after the formation of the LDSE.