PhD. Defense Rohan D. Kekatpure; Friday May 22 @2pm, Room CIS-X Auditorium

Rohan D. Kekatpure rohank at
Tue May 19 12:40:44 PDT 2009

TITLE: Challenges toward realizing silicon-nanocrystal-based lasers
and light sources

Rohan D. Kekatpure

Friday, May 22, 2:00 pm
CIS-X 101


The past decade has witnessed a dramatic surge in eliciting active
optical functionality out of silicon. Following successful
realizations of modulators, switches, and detectors, a silicon-based
electrically-pumped laser now remains the last challenge in heralding
the era of short-distance optical interconnects. In the year 2000,
evidence of optical amplification from silicon nanocrystals at visible
wavelengths, and Si-nanocrystal-sensitized erbium emission at 1550 nm
unlocked an encouraging route to overcome this obstacle. Despite its
disruptive technological significance, and the decade long hunt for
its realization, why is silicon-nanocrystal laser still an elusive

I will address this question by demonstrating how optical
microcavities can be used to quantify gain-limiting processes in
semiconductor quantum-dot ensembles. Specifically, I will highlight
our microcavity-based measurement of absorption processes in silicon
nanocrystals at visible and near-infrared wavelengths. Quite
surprisingly, we find that silicon nanocrystals show an increased free-
carrier absorption compared to bulk silicon. This finding has
initiated a rethinking of various existing strategies aimed at
obtaining optical amplification from silicon nanocrystals. A hurdle in
one path frequently proves to be a stepping stone in another: Can an
increased absorption in nanocrystals make them an alternative material
to SOI for making low-cost modulation and switching devices?

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