Electrical Excitation of Surface Plasmon Polaritons

Abstract

A surface plasmon polariton (SPP) is an electromagnetic wave propagating at the interface between a metal and a dielectric material. The two-dimensional confinement of SPPs and the tunability of their dispersion enable optical functionality that cannot be achieved with regular dielectrics. Several novel concepts for sensing and opto-electronic integration based on SPPs have been proposed. In nearly all applications, as well as experiments based on SPPs, far-field excitation of SPPs is used, leading to bulky device designs. This thesis presents an electrically excitable source for SPPs that can be integrated in small, chip-size devices to enable the full application potential of SPPs. The device is based on a dielectric/metal geometry in which silicon quantum dots are placed in the near-field of the SPP mode. The quantum dots are electrically excited and decay by the generation of SPPs. Silicon quantum dots in silica are made by a magnetron sputtering technique, followed by annealing. From photoluminescence spectra as well as lifetime measurements we conclude that well-passivated Si quantum dots with quantum confined luminescence around 800 nm can be made. An electrical injection geometry is presented and electroluminescence is observed around 650 nm under a bias of 15-30 V. Strong bleaching of the quantum dot luminescence is observed under 0.5-20 keV electron beam irradiation, which has a potential consequence for the use of electron beam lithography in nanofabrication of structures with Si quantum dots. We describe the design and the fabrication of an electrically excitable plasmon source based on an insulator-metal-insulator (IMI) geometry. The coupling of quantum dots to the SPP mode was studied theoretically. For quantum dots spaced 20-200 nm away from the metal surface, more than 50% of the decay is into SPPs. An IMI SPP geometry for electrical excitation was fabricated using gold and silica doped with Si quantum dots as dielectric material. An IMI SPP source in the infrared region was fabricated by incorporating erbium in the dielectric material. Using an SPP waveguide coupled to the source, with suitable engineered outcoupling gratings, we observed the propagation and outcoupling of electrically excited SPPs. The optical properties of Si quantum dots in alumina are studied. This material is deposited by using CMOS compatible, low-temperature techniques of atomic layer deposition (ALD) and low pressure chemical vapor deposition (LPCVD). Quantum-confined photo- and electroluminescence is observed at 700-900 nm. This material is used in a novel metal-insulator-metal (MIM) geometry. SPPs are electrically excited and propagate inside the MIM geometry and are radiated into the far-field by an outcoupling structure. The radiated intensity decays for outcoupling structures further away from the excitation source. The obtained propagation length is = 4.4 0.6 micron, which is in good agreement with the expected propagation length based on measured values of the dielectric constants. The last chapter of this thesis reports on several application ideas for the electrical SPP sources presented in this thesis. Integrated lab-on-a-chip devices, plasmonic (bio)sensors, nanoscale photonic integrated circuits, and a novel quantum dot solar cell geometry are proposed.