## 3 Results
### Electrical and Optical Characteristics of SiNW Photodetector  
Figure 8a shows the I-V characteristics of the 1 \(\times\) 5 SiNW photodetector in both the dark and illuminated states with a light intensity of 1.5 mW/cm\({}^{2}\) across a voltage range from 0 V to 1 V. The measurements obtained from each of the eight devices reveal linear characteristics under both conditions, confirming the establishment of an ohmic contact between the metal electrodes and the silicon device layer. Additionally, an increase in the light intensity leads to an increase in the photocurrent, which has the effect of decreasing the resistance of the SiNWs. In the dark state, holes are trapped at the surface of the nanowires, leading to complete depletion inside the photodetector and resulting in high resistance values, typically within the range of several mega-ohms. However, electron-hole pairs are generated when external light illuminates the nanowires, causing photoexcited electrons to populate the conduction band [31]. These excited electrons and trapped holes recombine at the surface, leaving holes in the core of the nanowire, which contributes to the generated current. Figure 8b illustrates the photocurrent responses of the three photodetectors, each comprising a SiNW structured into 1 \(\times\) 1, 1 \(\times\) 3, and 1 \(\times\) 5 arrays under varying light intensities. The three devices were subjected to broad-spectrum white light illumination, ranging from 0 mW/cm\({}^{2}\) (dark state) to 1.6 mW/cm\({}^{2}\) (10,000 lux) under a bias voltage of 3 V. Each device generated a greater photocurrent with the increase in the intensity of the illuminated light, which was distinguishable across a broad spectrum of light intensities. The devices exhibit higher photosensitivity with the increase in the density of the SiNWs owing to the enhanced surface-to-volume ratio. At 5000 lux, the photocurrents for the devices were measured at 5.5 \(\upmu\)A, 2.4 \(\upmu\)A, and 0.8 \(\upmu\)A, respectively. The near-linear increase in photocurrent with additional layers indicates that the effect of the upper layers on the lower layers is negligible during the photoreaction. All three devices exhibited high photosensitivity at low light intensities, and the rate of increase diminished with the increase in the light intensity. When SiNWs are illuminated, the electrons generated by the electron-hole pairs recombine with the surface carrier traps, while the photogenerated holes remain in the nanowires, contributing to an increase in the output current. At low illuminance, a gradual increase in the light intensity generates more electron-hole pairs, leading to a rapid increase in the photocurrent. However, at higher light intensities, the reduction in the density of the available carrier traps within the nanowire causes a photo-response saturation [32]. Thus, the SiNWs demonstrate high photosensitivity under low-light conditions, which can be advantageous in indoor lighting environments. Figure 8: Electrical and optical characteristics of the SiNW photodetector. (**a**) I–V characteristics of devices, 1 \(\times\) 5. (**b**) Photosensitivity across different light intensities correlated with the number of vertical SiNW layers under a bias voltage of 3 V.  
Figure 9a presents the results of an experiment evaluating the wavelength dependency of the photoresponsivity. The 1 \(\times\) 5 SiNW photodetector was illuminated with light of wavelengths ranging from 400 nm to 800 nm using a monochromator at a bias voltage of 3 V. A distinguishable photocurrent was measured at each wavelength. The power density peaked at 1.18 mW/cm\({}^{2}\) within the 400 nm wavelength range and decreased to 0.37 mW/cm\({}^{2}\) at the 800 nm wavelength range. The power density typically decreases with the increase in the wavelength, leading to a corresponding decrease in the photocurrent response.