# Photo-Thermoelectric Conversion of Plasmonic Nanohole Array
## 4 Conclusions  
A plasmonic photodetector consisting of a Ag thin-film with a nanohole array pattern was fabricated and investigated. The photodetection mechanism was examined by verifying the amount of plasmonic local heating, using both experimental and numerical methods. The wavelength dependence of EQE values was consistent with the extinction spectrum of the Ag nanohole, indicating that surface plasmon polaritons at the nanoholes played a dominant role in this photodetection mechanism. The calculated plasmonic local heating was a factor of 2.4 greater than the one estimated experimentally; however, our simulation technique for calculating plasmonic local heating is still a powerful tool to optimize the characteristics of this plasmonic photodetector. Calculated and measured extinction spectra confirmed that the wavelength of the surface plasmon polaritons of the Ag nanohole arrays is determined by the nanohole periodicity and dielectric constants for the surrounding media (Ag, air, resist). In other words, suitable design of nanohole periodicity, as well as appropriate selection of metals and surrounding media, will allow the realization of tunable photodetectors, not only for visible light but also in the near IR range. The external quantum efficiency and responsivity of the nanohole-array Ag thin-film device are \(3.1\times 10^{-3}\%\) and \(17.3\)\(\mu\)A/W, respectively, which are comparable with those of the respective levels for a plasmonic photodetector driven by hot carriers [3; 30] and are significantly lower than those of commercial Si detectors. However, there is ample scope for increasing EQE values, via optimization of device configurations, nanohole morphology, and appropriate material selection. Furthermore, our simple device configuration consisting of a single Ag nanofilm should help to ignite interest in the development of photodetectors that operate effectively on the nanoscale.  
The following are available online at [[http://www.mdpi.com/2076-3417/10/8/2681/s1](http://www.mdpi.com/2076-3417/10/8/2681/s1)]([http://www.mdpi.com/2076-3417/10/8/2681/s1](http://www.mdpi.com/2076-3417/10/8/2681/s1)), Figure S1: Schematic of illumination system, Figure S2: Calculated extinction spectrum, Figure S3: Electric current before and after illumination, Figure S4: Simulation models used for heat calculations.  
[PERSON] conceived the idea of this study. [PERSON] and [PERSON] performed sample fabrication and measurements. [PERSON] conducted the numerical simulations with support from [PERSON], [PERSON]; and [PERSON] wrote the manuscript. All authors contributed to the analysis and interpretation of results. [PERSON] supervised and coordinated all the work. All authors have read and agreed to the published version of the manuscript.  
This research was fully supported by the Casio Science Promotion Foundation, The Sumitomo Foundation, and the JSPS-Royal Society bilateral joint research program; and was partially supported by the JSPS Core-to-Core Program.  
The authors are grateful to [PERSON] for supporting simulations.  
The authors declare no conflict of interest.  
Figure 4: Dependence of plasmonic local heating on array size. Simulated local heating temperatures as a function of the numbers of nanoholes in the array (red circles). The dashed line indicates a logarithmic fit to the simulation results.