Researchers from the University of Illinois at Urbana-Champaign have recently received a patent for a novel type of laser that emits light between mid-IR wavelengths and terahertz frequencies. John Dallesasse and Milton Feng–both professors of electrical and computer engineering (ECE) and researchers at the Micro and Nanotechnology Laboratory (MNTL) at Illinois–think their transistor-injected quantum cascade laser (TI-QCL) may someday be used to test air and water quality, enhance semiconductor manufacturing, and improve early detection of cancer and other diseases.
According to Dallesasse, the TI-QCL essentially combines a heterojunction bipolar transistor (HBT) with a transistor laser, the latter being a device that Feng created with semiconductor laser and LED inventor Nick Holonyak Jr. in 2004.
“It had occurred to me that the QCL had a few things about it that were broken, but we could fix those things by putting in the base-collector junction of an HBT,” said Dallesasse, who joined the Illinois faculty in 2012 after a successful 20-year career in the optoelectronics industry.
As a two-terminal device, a conventional QCL is best suited for a single operating point and certain field.
“There’s not a lot of room to independently control wavelength and amplitude,” said Dallesasse.
Once the Illinois researchers added the third terminal, though, the TI-QCL gained independent control of field across, and current through, the quantum transition region. The end result is that the electric field controls wavelength while the current controls the laser power, which enhances the performance of the QCL.
As a sort of hybrid device, the TI-QCL can be fabricated on a range of substrates, with the collector contact made on the back of the wafer or with all the contacts made on the top surface. Fabrication of the device should also transfer easily to a commercial GaAs IC foundry.
“We think the advantages of our device are compelling because the [TI-QCL] will allow not only a lot of conventional QCL uses like gas detection, chemical sensing, and process monitoring, but it will also enable some interesting communications applications for free-space links,” said Dallesasse. “Applications in the THz region might also open up because of our device.”
ECE graduate student Kanuo Chen has developed code for modeling operation, designed the epitaxial layer structure, and fabricated devices. Kanuo is now beginning to test these devices and preliminary results are promising, Dallesasse said. This research was funded by a grant from the National Science Foundation.
Contact: John Dallesasse, Department of Electrical and Computer Engineering, University of Illinois at Urbana-Champaign, 217/333-8416,
Writer: Laura M. Schmitt, Micro and Nanotechnology Laboratory, University of Illinois at Urbana-Champaign, email@example.com.