# Neuromorphic Spatiotemporal Information Processing Using Neuro-Photodetector Systems
## 3 Results and Discussion
(**b**) Schematic drawings (not to scale) of a typical two-terminal photodetector shows response similar to artificial neuron with input optical pulses. (**c**) Response of a photodetector similar to artificial neuron. (**d**) Proposed working mechanism of the new concept optoelectronic device from (1) to (4) show the filling the defect levels with charge carriers. see Figure S2 (Supporting Information). Indeed, our presented approach provides a unique way to design, well, control geometry (e.g., rectangular, circular, etc. ), and size (from \(\upmu\)m to cm scale) of the devices over a desired area, see Figure S2 (Supporting Information). The growth of the ZnO nanofin was confirmed by planar-view scanning electron microscopy (SEM), as is presented in Figure 2b. It is interesting to note that ZnO thin film is closely packed, uniform, and conformally sandwiched between vertical Ag and Al, with a thickness of \(\sim\)80 nm. Following this the sandwiched nature of ZnO is confirmed by energy-dispersive x-ray spectroscopy (EDS), which shows the distribution of aluminum (Al), zinc (Zn), oxygen (O), silver (Ag) elements form the device, see Figure 2c. It is worth mentioning here that the growth of the ZnO by atomic layer deposition (ALD) has been characterized by various techniques and reported in our recent works. To understand the charge transport across the nanofin, the typical current-voltage (\(I\)-\(V\)) characteristics of the device in dark and with UV (intensity: 5 mW cm\({}^{-2}\)) illumination in the voltage scan range of \(-\)1.0 to +1.0 V (ramp rate; 0.01 V s\({}^{-1}\)) were performed and depicted in Figure 2d. The appearance of symmetrical curves under dark and with UV illumination conditions confirms the formation of Ohmic band alignment between the ZnO and Al/Ag. Under dark, the device shows low current (1.12 \(\upmu\)A at +1.0 V), which increases to 96.46 \(\upmu\)A with UV illumination. The resistance in dark (e.g., \(R_{\text{off}}\)) was found to be \(\sim\)1 M\(\Omega\), which decreases to \(R_{\text{on}}\)\(\sim\) 10.4 k\(\Omega\) with UV illumination (5 mW cm\({}^{-2}\)), confirming significant photocurrent switching on/off ratio (\(I_{\text{p}}\)/\(I_{\text{dark}}\)) up to \(\sim\)10\({}^{2}\), see Figure 2d. In fact, the \(e\)-\(h\) pairs generated within the ZnO with UV illumination and, thus, the \(I_{\text{p}}\) increases at every measuring voltage. Further, the transient-photorespone (\(I_{\text{p}}\)-\(t\)) was measured at +0.6 V after being illuminated with a single UV pulse (4 mW-cm\({}^{-2}\), time, \(\Delta t\) = 1 s), see inset of Figure 2d. During the UV illumination, the \(I_{\text{p}}\) increases rapidly, while it decreases gradually after switching off, indicating the band-to-band excitations and recombination of \(e\)-\(h\) pairs, respectively [4; 14; 16]. This observation in fact indicates that the device shows significant response to a single UV pulse. In addition, the device shows slow photocurrent decay after UV illumination, the possible reason could be the charge trapping/detrapping  
Figure 2: Schematic and device characterization. (**a**) Device schematic, (**b**) planar-view SEM of the ZnO nanofin sandwiched between Al and Ag thin film, (**c**) corresponding elemental distribution of the Al, Zn, O, and Ag from energy-dispersive X-ray spectroscopy (EDS) measurements, clockwise. The scale bar is 1 \(\upmu\)m. (**d**) Current–voltage characteristics of the device under dark and with different UV illumination, showing photocurrent generation. The inset of (**d**) shows the device retention measurements at +0.6 V, after applying a single UV pulse. (**e**) The change in photocurrent (\(I_{\text{p}}\)) as a function of light intensity. (**f**) The photocurrent generation due to different areas. by oxygen vacancy. The slow decay of the \(I_{\rm p}\) in ZnO-based devices has been explained on the basis of the reaction of UV induced holes with chemisorbed surface oxygen, such as h\({}^{+}\) + O\({}^{2-}\)(ad) = O\({}_{2}\)(g) [4].