Two ECE graduate students win best poster awards at International Nano-Optoelectronics Workshop
By Shawn Adderly, ECE ILLINOIS
October 15, 2010
- ECE graduate students Chien-Yao Lu and Akira Matsudaira each won a Best Poster Award at the International Nano-Optoelectronic Workshop held recently in China.
- Lu's detailed a the fabrication process of a microlaser that is substrate free and able to operate at room temperature.
- Matsudaira's poster demonstrated how metal coating adjacent to a laser's active region increased the group refractive index and operational temperature limit of a laser.
Last month ECE graduate students Chien-Yao Lu and Akira Matsudaira came back to Champaign from their long transcontinental flight with awards after they were both recognized for their posters that were presented at the International Nano-Optoelectronic Workshop held in Beijing and Changchun China in August. The workshop was supported by National Science Foundations of USA and China, Berkeley Nanosciences and Nanoenigneering Institute, and a few other institutions.
The invitation-only workshop for academics and industry participants focused on highlighting advances in nanoscale semiconductor processing, characterization, and new devices. Lu and Matsudaira won the first and third place Best Poster Award, respectively, out of about 130 posters entered into the competition.
Lu’s poster, titled “Substrate-Free Metal Cavity Surface Emitting Microlaser at Room Temperature,” detailed the fabrication process of a microlaser that is substrate free, smaller than previous metal cavity devices with bulky substrates, and easily integratable to silicon substrate or another device. Matsudaira's poster, titled "Metal-Coated Quantum-Dot Lasers,” showed that a metal coating on lasers enable improved performance at higher temperatures.
Their projects are very applicable as copper wires reach their physical limits and optical interconnects are recognized as the emerging alternative.
Lu fabricated his microlaser using a sample designed with ECE Professor Shun Lien Chuang. The sample was grown by their collaborator Tim Germann in Professor Dieter Bimberg's group at the Technical University of Berlin. The device consists of an active region with GaAs/AlGaAs multiple quantum wells that are sandwiched between silver (Ag) and a distributed Bragg reflector. The wells are then sandwiched between silicon nitride and silver to form an optical cavity. After flip bonding the device directly to a silicon substrate, the GaAs substrate was etched and removed, resulting in a physical dimension of the device to be only 2 micrometers in diameter and 2.5 micrometers in total thickness.
“People always think of metal as being a lossy material, and that lasers using lossy material won’t work at room temperature,” Lu said. “However we made it work because of the substrate-free and top-emission configuration of our device, and produce a continuous output beam.”
Lu’s fabrication method could have potential use in preventing crosstalk in parallel dense optical interconnects.
Matsudaira discovered that metal coating adjacent to a laser’s active region increased the group refractive index and operational temperature limit of the laser. His metal-coated laser consisted of 10 layers of InAs/GaAs quantum dots (QDs). Gold and silver were chosen for the coatings because they have much smaller optical absorption than other metals in the infrared wavelength. Lasers with high characteristic temperatures are ideal since heating can affect some static and dynamic features of the device once it reaches above the threshold.
“Potentially, this may reduce the cost of installing the device, since most lasers used in the field have an active cooling device,” Matsudaira said. “This could remove the need for external hardware.”
Lu said that since metal-coated lasers are less sensitive to changes in temperature they can be used in more harsh environments, such as in instruments used to monitor chemicals during processing.
Chuang, doctoral adviser for both students, said he was very proud that his students managed to claim the top awards at the workshop.
“It’s because of their hard work. They are both very intelligent and well prepared students,” Chuang said.
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