Nav: Home

Extending VCSEL wavelength coverage to the mid-infrared

February 14, 2017

WASHINGTON, D.C., February 14, 2017 -- Vertical-cavity surface-emitting lasers (VCSELs) are small, semiconductor-based lasers that emit optical beams from their top surface, and one of their main applications is in gas sensing. Gases each have a unique set of energies they can absorb, derived from their molecular structure. These sets of absorption lines are akin to fingerprints, which enables unambiguous and sensitive detection with a suitable tunable laser like a tunable VCSEL.

There are several important gases that are detectable with mid-infrared (mid-IR) light, having wavelengths between 3 and 4 micrometers (microns), including methane, carbon dioxide and nitrogen dioxide. Application-grade VCSELs, however, aren't yet available for this wavelength range, but the increasing need for compact, portable and affordable gas sensors is spurring demand for energy-efficient semiconductor sources of mid-IR light.

Addressing this demand, a group of researchers from the Walter Schottky Institute at the Technical University of Munich (TUM) in Germany set out to develop a concept to extend the wavelength coverage of VCSELs into this important regime, which they report this week in Applied Physics Letters, from AIP Publishing.

Typical VCSELs suffer in performance for the relatively long wavelengths of the mid-IR range, in part due to side effects of heating that disproportionally affect IR wavelengths. These effects are minimized by the "buried tunnel junction" configuration of VCSELs, where a material barrier is embedded between the standard p- and n-type materials of the semiconductor. This structuring results in resistancelike behavior for the device and provides tunability of the optical properties in the desired range.

"The buried tunnel junction VCSEL concept has already yielded high-performance VCSELs within the entire 1.3- to 3-micron wavelength range," said Ganpath K. Veerabathran, a doctoral student at the Walter Schottky Institute. "And so-called type-II 'W' quantum well active regions have been used successfully to make conventional edge-emitting semiconductor lasers with excellent performance within the 3- to 6-micron wavelength range."

By combining the tunnel junction VCSEL concept with these conventional edge-emitting laser designs, where the beam is emitted in parallel with the bottom surface, in this wavelength regime, the researchers created a buried tunnel junction VCSEL with a single-stage, type-II material active region to extend the wavelength coverage of electrically pumped VCSELs.

This advance is particularly noteworthy because it's the first known demonstration of electrically pumped, single-mode, tunable VCSELs emitting continuous wave up to 4 microns.

"It marks a significant step from state-of-the-art devices emitting at three microns in a continuous wave, and up to 3.4 microns in pulsed mode, respectively," said Veerabathran. "Further, our demonstration at four microns paves the way for application-grade VCSELs within the entire 3- to 4-micron wavelength range, because the performance of these VCSELs generally improves at shorter wavelengths."

It's important to note that although gas-sensing systems within this wavelength range are already available using other types of lasers, they're considered to be power hogs compared to VCSELs. They also tend to be cost-prohibitive, and are mainly used by industries to detect trace gases for safety and monitoring applications.

"The 4-micron VCSEL demonstrates that low-power, battery-operated, portable and inexpensive sensing systems are within reach," Veerabathran also said. "Once sensing systems become more affordable, there's great potential for deployment by industries, such as the auto industry for emission monitoring and control, and these systems may even find uses within our homes."

Next, the group will focus on making improvements "in terms of the maximum operation temperature and optical output power of the VCSELs," Veerabathran said. "In the future, it may be possible to extend this concept to make VCSELs emit further into the mid-infrared region beyond 4 microns. This would be beneficial because the absorption strength of gases typically becomes orders of magnitude stronger, even for relatively small wavelength increases."
-end-
The article, "Room-temperature vertical-cavity surface-emitting lasers at 4 μm with GaSb-based type-II quantum wells," is authored by Ganpath Kumar Veerabathran, Stephan Sprengel, Alexander Andrejew and Markus-Christian Amann. The article appeared in the journal Applied Physics Letters Feb. 13, 2017 (DOI: 10.1063/1.4975813) and can be accessed at http://aip.scitation.org/doi/full/10.1063/1.4975813.

ABOUT THE JOURNAL

Applied Physics Letters features concise, rapid reports on significant new findings in applied physics. The journal covers new experimental and theoretical research on applications of physics phenomena related to all branches of science, engineering, and modern technology. See http://apl.aip.org.

American Institute of Physics

Related Semiconductor Articles:

Researchers repurpose failed cancer drug into printable semiconductor
Many potential pharmaceuticals end up failing during clinical trials, but thanks to new research from the University of Illinois, biological molecules once considered for cancer treatment are now being repurposed as organic semiconductors for use in chemical sensors and transistors.
Clarification of a new synthesis mechanism of semiconductor atomic sheet
Researchers at Tohoku University in Japan succeeded in clarifying a new synthesis mechanism regarding transition metal dichalcogenides (TMD), which are semiconductor atomic sheets having thickness in atomic order.
Future of portable electronics -- Novel organic semiconductor with exciting properties
Organic semiconductors have advantages over inorganic semiconductors in several areas.
A new method for quantifying crystal semiconductor efficiency
Japanese scientists have found a new way to successfully detect the efficiency of crystal semiconductors.
X-rays reveal monolayer phase in organic semiconductor
An international team of researchers has investigated how the electrical properties of dihexyl-quarterthiophene thin films depend on their structure.
More Semiconductor News and Semiconductor Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Rethinking Anger
Anger is universal and complex: it can be quiet, festering, justified, vengeful, and destructive. This hour, TED speakers explore the many sides of anger, why we need it, and who's allowed to feel it. Guests include psychologists Ryan Martin and Russell Kolts, writer Soraya Chemaly, former talk radio host Lisa Fritsch, and business professor Dan Moshavi.
Now Playing: Science for the People

#537 Science Journalism, Hold the Hype
Everyone's seen a piece of science getting over-exaggerated in the media. Most people would be quick to blame journalists and big media for getting in wrong. In many cases, you'd be right. But there's other sources of hype in science journalism. and one of them can be found in the humble, and little-known press release. We're talking with Chris Chambers about doing science about science journalism, and where the hype creeps in. Related links: The association between exaggeration in health related science news and academic press releases: retrospective observational study Claims of causality in health news: a randomised trial This...