Quantum cascade lasers that emit more light than heat

For any semiconductor lasers, the wall plug efficiency, that is, the portion of the injected electrical energy that can be converted into output optical energy, is one of the most important figures of merit. A device with a higher wall plug efficiency has a lower power demand and prolonged device lifetime due to its reduced self-heating. Since its invention, the power performance of the quantum cascade laser(1) has improved tremendously(2-7). However, although the internal quantum efficiency(7,8) can be engineered to be greater than 80% at low temperatures, the wall plug efficiency of a quantum cascade laser has never been demonstrated above 50% at any temperature. The best wall plug efficiency reported to date is 36% at 120 K (ref. 9). Here, we overcome the limiting factors using a single-well injector design and demonstrate 53% wall plug efficiency at 40 K with an emitting wavelength of 5 mu m. In other words, we demonstrate a quantum cascade laser that produces more light than heat.