Engineering localized surface plasmons in doped semiconductor nanomaterials

Abstract

Doped semiconductors materials have emerged as the preeminent materials platform for development of optoelectronic technologies harnessing the LSPR phenomena in the infrared spectral regime. The capacity to engineer a plasmonic spectral response via doping for optoelectronic applications in the infrared is a proposition of semiconductor nanomaterials pursued in this dissertation. In Chapter 2, we show the impact of axially carrier density gradients on the spectral response of Si nanowires containing multiple resonators. We couple in situ infrared spectral response measurements and discrete dipole approximation (DDA) calculations to show the impact of axially graded carrier density profiles on the optical properties of mid-infrared LSPRs supported by Si nanowires synthesized by the vapor-liquid-solid technique. In Chapter 3, we first demonstrate that embedding resonators in an anisotropic dielectric with a large permittivity can dramatically increase the LSPR coupling interaction strength and thereby, plasmonic spectral extinction and near-field intensity. We experimentally show this effect with Si nanowires containing two phosphorus-doped segments. Lastly, in Chapter 4 we first demonstrate infrared photoconductivity within the Al2O3 coated ITO nanocrystal films, and show that infrared photocurrent in these materials exhibits an exclusive relationship with LSPR absorption in the same regime. Measurements using a broadband infrared source and a voltage bias of 10V, yield a responsivity of 15 A/W and a detectivity of 1.2 108 cmHz1/2W-1. The experimental studies and theoretical analysis which are outlined in this dissertation, demonstrate and substantiate the advantages of doped semiconductor nanomaterials in engineering and harnessing infrared LSPRs for next-generation optoelectronic technologies.