Today : University PhD Dissertation Defense for Justin White : 2:15pm in Packard 202

Department of Applied Physics

University PhD Dissertation Defense

Surface Plasmon Enhanced Photodetectors

Justin Stewart White

Research Advisor: Professor Mark Brongersma

16 February 2010  @2:15 p.m.

(Refreshments at 2:00 p.m.)

Location: Packard Building, Room 202

ABSTRACT

Photodetectors play an increasingly vital role in information technology, forming the basis of modern fiber-optic communication systems as well as digital imaging for consumer, medical, and scientific applications.  Innovation in the design and fabrication of photodetectors has been a key enabler in the drastic reduction in size of digital cameras such that a five megapixel camera can now be embedded in a cell phone, as well as the scaling of fiber-optic networks from transcontinental networks spanning hundreds of kilometers down to local networks within a server room spanning several meters.  However, further scaling is inhibited by the fundamental diffraction limit of classical optics, which limits the ability to make efficient optical components at the nanoscale.  In this talk I will present our work on utilizing surface plasmon polaritons, coherent electron oscillations coupled to a photon and bound to a metal-dielectric interface, to make semiconductor photodetectors with sub-wavelength active regions well below the classical diffraction limit and the optical absorption depth of the semiconductor.

We theoretically investigate plasmon enhanced photodetector designs using finite-difference frequency domain (FDFD) numerical simulations of Maxwell's equations.  FDFD simulations are particularly well suited to modeling plasmonic devices because they can handle dispersive materials, such as metals, without approximation and adaptive grid spacing for structures with disparate length scales.  FDFD simulations are used to characterize and optimize silicon photodetectors with integrated resonant plasmonic structures.  By properly optimizing the resonant structures, near-field absorption in the silicon can be enhanced up to 350%, a phenomenon known as extraordinary optical absorption (EOA).

We experimentally investigate these devices by fabricating resonant plasmonic nano-structures in aluminum and gold films on bulk silicon and silicon-on-insulator devices.  We find good agreement with theoretically predicted properties, and experimentally measure absorption enhancements up to 300%.  Finally, we investigate silicon detector devices integrated with deep sub-wavelength plasmonic waveguides.  Such devices are promising for optical interconnects directly integrated with modern microprocessors.