Surface Plasmon Enhanced Optoelectronic Devices

Abstract

Surface Plasmon Polaritons (SPPs) are electromagnetic waves coupled to the free electrons at the surface of metals, which propagate along the interface of metal and dielectric at optical frequencies. SPPs have found many applications in communications, sensing, and photovoltaics, among others, due to their subwavelength confinement and high sensitivity. These qualities can significantly reduce device footprint, while enhancing device performance. This thesis investigates three novel surface plasmon enhanced optoelectronic device concepts, namely two photodetectors and an electro-optic intensity modulator, at wavelengths in the photonic C-band. It is demonstrated, theoretically and numerically, that involving SPPs improves speed and sensitivity of these devices, while significantly reducing their dimensions, compared to conventional counterparts. The first device proposed and investigated is a photodetector which employs arrays of nanodipoles, as a plasmonic metasurface, in order to localize light in subwavelength InGaAs detection regions, placed within the gaps of Au nanodipoles. As a result, the speed-responsivity trade-off, which is common in conventional photodetectors, is overcome. Numerically, responsivities of 100 mA/W and electrical bandwidths of up to 4 THz are predicted. The second device is a photodetector which exploits tightly confined SPPs generated in a film of InGaAs, covered by arrays of Au nanomonopoles. By carefully designing these arrays of nanomonopoles, responsivities up to 200 mA/W were achieved for electrical bandwidths as high as 1 THz, at the wavelength of 1550 nm. Finally, the fabrication of an electro-optic intensity modulator, incorporating grating couplers, is demonstrated and discussed. Modulation is based on enhanced perturbation of the effective refractive index of grating-coupled surface plasmon polaritons propagating along a metal–oxide–semiconductor structure on silicon. A front-side probing technique was employed, which enabled modulation in transmission, as well as reflection. Lithography techniques were optimized to produce high resolution devices.