By bonding an III-V layer directly on top of a silicon wafer and then using the III-V layers to generate gain for the laser, the group has integrated a multiple quantum well laser on silicon. The device is said to operate at a wavelength of 2µm.
Building a quantum cascade laser on silicon was made more difficult because silicon dioxide becomes heavily absorptive at longer wavelengths in the mid-infrared. “This meant that not only did we have to build a different type of laser on silicon,” Spott explained, “we had to build a different silicon waveguide too.
“We built a type of waveguide called a SONOI waveguide, which uses a layer of silicon nitride underneath the silicon waveguide, rather than just SiO2.”
The next step for the team is to improve the heat dissipation. “We generally hope to improve the design to get higher powers and efficiency,” Spott said. “This brings us closer to building fully integrated mid-infrared devices on a silicon chip, such as spectrometers or gas sensors. Silicon is inexpensive, the fabrication can be scaled up to significantly reduce the cost of individual chips, and many small devices can be built on the same silicon chip for example multiple different types of sensors operating at different mid-infrared wavelengths.”
