Plasmonics in Semiconductors

Abstract

This thesis establishes a mathematical, physical and experimental framework for description, characterization, and application of semiconductor plasmonic properties. Plasmonic phenomena in semiconductors are found in the Terahertz and far-infrared domain, where they have the potential to improve sensors or be the basis of novel devices. III-V semiconductor samples (GaAs, InP, InSb, and InAs) with various doping were analyzed spectroscopically in broad spectral range. Fourier Transform Infrared Spectroscopy together with Terahertz time-domain spectroscopy were used for characterization of the free carrier (plasmonic) and lattice (phononic) optical properties of the samples. The Drude-Lorentz model was used to describe these properties, with the addition of magneto-optical (MO) effects. High mobility semiconductors (InSb and InAs) exhibit huge free carrier magneto-optical effect for small external magnetic field. These measurements were compared to electric Hall effect measurement using Van der Pauw method.

Based on the spectroscopic and MO characterization of the samples, the applicability of semiconductor as plasmonic materials is discussed. Huge advantage of semiconductors is the tunability their plasmonic properties. Three methods of controlling the plasmonic behavior of semiconductors were analyzed: Shifting of plasma frequency to higher frequencies by increasing of n-type doping concentration. Modification of the material permittivity (conductivity) tensor spectra by the external magnetic field. Shifting of plasmonic resonance by generation of nanogratings in the material, either by carrier concentration modulation by interference light illumination (sinusoidal grating) or by lithography (lamellar grating). The effective medium approximation of nanogratings was verified using Rigorous Coupled Wave Analysis.

An experimental application of widely tunable THz surface plasmon resonance sensor on semiconductors is presented. Generation of surface plasmon polariton at the interface between undoped InSb(InAs) and dielectric is experimentally demonstrated. This sensor has the added functionality of strong magnetic tuning. The applicability of this sensor is discussed, along with analysis of different sensor architecture.