Optical Enhancement in Periodic Plasmonic Gratings for SERS and Metal-Semiconductor-Metal Photodetectors (MSM-PDs) Applications

This dissertation is aimed to numerically study the effect of plasmonic grating electrodes on the efficiency of metal-semiconductor-metal photodetectors (MSM PDs) and the sensitivity of Surface Enhanced Raman Spectroscopy (SERS). This research can benefit many areas of nanoscience and optics, including plasmonic applications, such as, super lenses, nano-scale optical circuits, optical filters, surface plasmon enhanced photo-detectors solar cells, imaging sensors, charge-coupled devices (CCD), and optical-fiber communication systems. Several parameters, wire widths and thickness, gap space, taper angle, and the incident wavelength and angle, were investigated. The goal of this research is to utilize the plasmonic phenomenon by using plasmonic gratings to develop and improve detectivity of metal-semiconductor-metal photodetectors (MSM-PDs) and sensitivity of SERS. The dissertation includes the study of the substrate type ‒ SiO2 and SiO2/Si for SERS applications, and GaAs substrates for MSM PDs ‒ on the optical enhancement. In addition, the impact of the period of the nanograting, single and dual-width structures, is examined as well. Then, a comparison is conducted between these types to determine the optimum periods. The results show that dual-width structures can improve the incident light two times more than the single-width structures. The work also introduces a new method, which incorporates the current density of the device when calculating the overall current enhancement in order to model real performance more accurately. Using this method indicates that since plasmonic hot spots align well with areas of large current density, the optical enhancement can play an even larger role in total current improvement. The impact of taper angles, positive and negative, is also studied in detail. The results suggest significant optical enhancements can be achieved by using tapered nanoslits instead of vertical sidewall structures. Finally, the effect of the incident wave angle on the enhancements is considered as well. Interestingly, the results show a significant role that incident wave angle can play on both the incident light enhancements