Oleg B. Shchekin talks with
ScienceWatch.com and answers a few questions about
this month's Fast Moving Front in the field of
Engineering.
Article: 1.3 mu m InAs
quantum dot laser with T-o=161 K
from 0 to 80 degrees C
Authors: Shchekin,
OB;Deppe, DG
Journal: APPL PHYS LETT, 80 (18): 3277-3279 MAY 6
2002
Univ Texas, Dept Elect & Comp Engn, Microelect Res Ctr,
Austin, TX 78712 USA.
Univ Texas, Dept Elect & Comp Engn, Microelect Res Ctr,
Austin, TX 78712 USA.
Why do you think your paper is highly
cited?
This paper is of high significance for multiple reasons. It introduced a
powerful method for enhancing quantum dot (QD) laser performance,
demonstrated record QD laser operating characteristics, and at the same
time, offered QD lasers advantages for use in practical applications.
Does it describe a new discovery, methodology, or
synthesis of knowledge?
The paper introduced and demonstrated a way to dramatically increase
optical gain of QD active regions at practical levels of current injection,
as well as reduce the dependence of optical gain and, consequently, laser
threshold current on temperature. QD lasers, as a concept, were introduced
quite some time ago.
"This paper
describes the results of a first
set of experiments we performed to
test the results of
calculations."
These lasers were forecast to have extremely high differential gain and
temperature independent threshold currents, all due to an idealistic
concept of discrete density of thermally independent energy levels within
quantum dots. The practical III-V semiconductor self-assembled QDs have
closely spaced hole energy levels, which, as we realized, would reduce hole
occupancy of the energy levels participating in lasing. As a result,
optical gain would become very temperature dependent.
Would you summarize the significance of your paper in
layman's terms?
Our paper has shown that by incorporating acceptors in near proximity to
QDs, one could force the holes into the ground state to counteract their
thermalization out of ground states. The experimental results reported in
the paper showed, at that time, record levels of insensitivity to
temperature for semiconductor lasers operating at 1.3 micron (the
wavelength important for fiber-optic communications). The practical
application of this work was immediate: it introduced a semiconductor laser
which needed a much cheaper infrastructure than that required by current
drivers and packaging.
How did you become involved in this research and were
there any particular problems encountered along the way?
I was introduced to the concept of QD lasers by one of the leading
researchers in the field, Dennis Deppe, Professor of Optics and the FPCE
Endowed Chair in the College of Optics & Photonics at the University of
Central Florida.
By the time of publication, I had spent four years in his lab working on QD
epitaxy and laser fabrication. Dennis pointed me in the direction of using
dopants to alter electro-optical properties of QDs. Together we performed a
set of calculations which pointed to the resulting decrease in temperature
insensitivity of threshold and potentially high differential gain. This
paper describes the results of a first set of experiments we performed to
test the results of calculations.
Where do you see your research leading in the
future?
At present, QD lasers are starting to become commercialized for short-haul
fiber-optic communications. In the future, QDs have potential for impact in
the field of nano-photonics.
As has been shown by our collaborators and other researchers, single QDs
can be incorporated in photonic nano-cavities which allow study of light
interaction with discrete energy levels of QDs and hold promise for use in
on-chip data-links for ultrafast computing. In single QD photonic devices,
charge control due to proximity-placed dopants will greatly affect carrier
capture and recombination dynamics and also can finally realize the promise
of enhanced differential gain.
Do you foresee any social or political implications for
your research?
Most of our work is directed towards faster information transfer and
processing, which has potential for enhancing our quality of life. My
feeling, though, is that any change resulting from this research will be
gradual and a part of the evolution of existing data technologies.
Oleg Shchekin, Ph.D.
Senior Scientist, Advanced Laboratories
Philips Lumileds Lighting Company
San Jose, CA, USA