PhD Dissertation Defense for Luke Tang on June 19

Luke Tang Luke_Tang at stanford.edu
Mon Jun 16 14:56:13 PDT 2008


>
>
>Department of Applied Physics
>University PhD Dissertation Defense
>
>Nanometre-Scale Photodetectors Enhanced by Optical Antennas
>
>Liang (Luke) Tang
>
>Research Advisor: Professor David A.B. Miller
>
>June 19, 2008 @ 3:00 p.m.
>in
>Center for Integrated Systems (CIS-X), Auditorium room 101
>
>Abstract
>
>The use of optics to make connections within and 
>between electronic chips has been the subject of 
>research for over 20 years because it could 
>solve many of the problems experienced in 
>electrical systems. A critical challenge for the 
>convergence of optics and electronics is that 
>the micrometre scale of optics is significantly 
>larger than the nanometre scale of modern 
>electronic devices. In the conversion from 
>photons to electrons by photodetectors, this 
>size incompatibility often leads to substantial 
>penalties in power dissipation, area, latency 
>and noise. A photodetector can be made smaller 
>by using a subwavelength active region which, 
>however, could result in very low responsivity 
>because of the diffraction limit of the light.
>In our first approach to tackle this problem, we 
>use a C-shaped nano-aperture antenna in a thin 
>metal layer to enhance the photocurrent response 
>of a subwavelength photodetector. The work is 
>the first demonstration of a plasmonic-enhanced 
>semiconductor photodetector at near-infrared 
>wavelengths. In our second approach, we exploit 
>the idea of a dipole antenna from radio waves, 
>but at near infrared wavelengths (~ 1.3 µm), to 
>concentrate radiation into a nanometre-scale Ge 
>photodetector. Despite the small antenna size (~ 
>380 nm long) and the different properties of 
>metals at such high frequencies (~ 230 THz), the 
>antenna has qualitatively similar behavior to 
>the common radio-frequency half-wave Hertz 
>dipole. It gives a relative enhancement of 20 
>times in the resulting photocurrent in the 
>subwavelength Ge detector element, which has an 
>active volume of 0.00072 _m3, two orders of 
>magnitude smaller than previously demonstrated 
>detectors at such wavelengths. Finally, we 
>integrate an antenna-enhanced photodetector on a 
>commercial CMOS chip, which is the first 
>demonstration of any plasmonic effect in Si 
>CMOS. Photodetectors are one of the most 
>critical components in optoelectronic 
>integration, and decreasing their size may 
>enable novel chip architectures and ultra-low 
>electrical and optical power operations.
>
>
>--
>--++**==--++**==--++**==--++**==--++**==--++**==--++**==
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