Novel Design May Make QCLs More Efficient, Easier to Produce

Quantum cascade lasers (QCLs) developed using just two different materials have been demonstrated to be performance-comparable to QCLs manufactured using more costly, complicated methods. Previous approaches to QCL production have required the QCL to be situated atop a substrate comprised of more than 1,000 layers. Each layer, barely thicker than a single atom, was composed of one of five different materials, making production challenging and expensive.

Researchers at the University of Central Florida (UCF) have developed a simpler process for creating QCLs. The researchers’ use of just two materials resulted in a design that is simpler to produce, and yet is comparable in performance and higher in efficiency than QCLs made using more complex methods.

Assistant professor Arkadiy Lyakh of UCF's NanoScience Technology Center has developed the most efficient quantum cascade laser ever. Courtesy of University of Central Florida.

"The previous record was achieved using a design that's a little exotic, that's somewhat difficult to reproduce in real life," professor Arkadiy Lyakh said. "We improved on that record, but what's really important is that we did it in such a way that it's easier to transition this technology to production. From a practical standpoint, it's an important result."

The research team produced 5.6-μm QCLs with a measured pulsed room temperature wall plug efficiency of 28.3 percent. They tested devices with variable cavity lengths and measured an injection efficiency of 75 percent for the upper laser level. They measured a threshold current density of 1.7 kA/cm² and a slope efficiency of 4.9 W/A for uncoated 3.15-mm × 9-μm lasers. Threshold current density and slope efficiency dependence on temperatures ranging from 288 K to 348 K for the structure could be described by characteristic temperatures T0 ∼ 140 K and T1 ∼ 710 K, respectively.

The ability to produce QCLs more efficiently could lead to their greater use in spectroscopy, such as use of the IR lasers as remote sensors to detect gases and toxins in the atmosphere. Lyakh also envisions their use in portable health devices. For instance, a small QCL-embedded device could be plugged into a smartphone and used to diagnose health problems by simply analyzing one's exhaled breath.

"But for a handheld device, it has to be as efficient as possible so it doesn't drain your battery and it won't generate a lot of heat," Lyakh said.

The research was published in Applied Physics Letters (doi: 10.1063/1.4963233)