## 3 Results  
Figure 2 is a Scanning Electron Microscope (SEM) image of the silicon micropillars with no SiO\({}_{2}\) deposition. It was seen that the diameter of the pillars was 3.952 \(\upmu\)m. Figure 3 shows a SEM image of the silicon micropillar with silicon oxide deposited on the pillars. It was seen that the diameter of the pillars was 4.170 \(\upmu\)m.  
X-ray Photoelectron Spectroscopy (XPS) measurements were performed in order to study the depth profile of phosphorus in all the samples. XPS is a tool used for surface analysis. The X-ray depth penetration is about 10 \(\upmu\)m, but only the top 10 nm can emit photoelectrons. Figure 4 shows the dopants depth and atomic percentage of Phosphorus in sample A (no oxide layer) and sample B (oxide layer). Sample A showed that with no SiO\({}_{2}\) layer, the phosphorus concentration at 5 nm depth was 8% (\(4\times 10^{21}\) cm\({}^{-3}\)) and the atomic percentage dropped to \(\approx\)2% at 15 nm. Sample B showed that with SiO\({}_{2}\) used as a blocking layer, the phosphorus concentration was 4% at the surface and dropped to  
Figure 1: Image (**a**) represents the desired radial p–n junction [15], image (**b**) represents the radial p–n junction obtained when the micropillars were doped with the same method used to dope planar silicon wafers, and image (**c**) is the potential radial p–n junction with the proposed doping method.  
2% at 15 nm. These results show that the concentration of phosphorus and the slope of concentration vs. depth can be controlled by using SiO\({}_{2}\).  
Figure 5 depicts the I-V profile of sample B (oxide layer). The voltage was swept from \(-5\) V to 5 V, and the current was measured. It was observed that a Schottky contact was obtained, where at 5 V the dark current was 0.2 mA/cm\({}^{2}\) and the light current was 0.3 mA/cm\({}^{2}\). The addition of the silicon oxide insulating layer could play a role in enhancing the solar cell's current output by reducing the cell's saturation current.  
Figure 3: Micropillars with oxide layer. The diameter of the pillar is 4.17 \(\upmu\)m.  
Figure 2: Micropillars without oxide layer. The diameter of the pillar is 3.952 \(\upmu\)m.  
A p-n junction is characterized by its saturation current, I\({}_{0}\), which is the sum of the minority saturation current and majority carrier saturation current. It is known that high saturation current hurts the performance of solar cells. Adding an insulating layer between the semiconductor and the metal can reduce the saturation current due to the majority carriers without impacting significantly the short-circuit current which is a result of minority carriers tunneling through the insulator, as shown in Figure 6. The main cause of this phenomena is because the electric field drives the minority carriers towards the barrier, where they can accumulate to tunnel through. The majority carriers on the other hand are pushed away from the interface electric field. This means slowing their passage can significantly reduce their current flow. Thus, creating a Metal-Insulator-Semiconductor (MIS)  
Figure 4: Atomic percentage of phosphorous in sample A (no oxide layer/legend with red circles) and sample B (oxide layer/legend with blue squares).  
Figure 5: I-V profile of sample B (the sample with an oxide layer).  
contact instead of a Metal-Semiconductor (MS) contact can have the added advantage of reducing the saturation current of the solar cell.