Terahertz difference-frequency quantum cascade laser sources on silicon

Terahertz quantum cascade laser sources based on intra-cavity frequency mixing are currently the only monolithic electrically pumped semiconductor devices that can operate in the 1–6 THz spectral range at room temperature. The introduction of the Cherenkov waveguide scheme in these devices grown on semi-insulating InP substrates enabled generation of tens of microwatts of average terahertz power output and wide spectral tunability. However, terahertz radiation outcoupling in these sources is still highly inefficient. Here we demonstrate that an application of the III–Von- silicon hybrid laser concept to terahertz quantum cascade laser sources based on Cherenkov intra-cavity differencefrequency generation dramatically improves their output power and mid-infrared-to-terahertz conversion efficiency. The best-performing device transfer-printed on a float-zone high-resistivity silicon substrate produced 270 μW of peak power output at 3.5 THz at room temperature, a factor of 5 improvement over the best reference devices on a native semi-insulating InP substrate.