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FAST MOVING FRONTS - 2008

Oleg B. Shchekin talks with ScienceWatch.com and answers a few questions about this month's Fast Moving Front in the field of Engineering.
Shchekin 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.

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

Keywords: quantum dot (QD) laser, QD lasers, III-V semiconductor self-assembled QDs, quantum dots, lasing, thermalization, semiconductor lasers, fiber-optic communications, dopants, electro-optical properties, QDs, nano-photonics, QD photonic devices, photonic nano-cavities, light interaction, discrete energy levels, proximity-placed dopants, recombination dynamics, enhanced differential gain

  



2008 : May 2008 - Fast Moving Fronts : Oleg B. Shchekin