Single-mode tapered terahertz quantum cascade lasers with lateral gratings

•Tapered terahertz quantum cascade lasers with lateral gratings have been designed and fabricated.•The proposed device exhibits low lateral divergence and single-mode operation.•The proposed device also has advantage of easy fabrication.

We report on tapered terahertz quantum cascade lasers with lateral gratings. The proposed devices exhibit not only low horizontal divergence due to tapered structure but also single-mode operation by using lateral grating structure. The tapered region and lateral gratings can be fabricated with the ridged waveguide in one etching step without inducing complexity into the fabrication. Side-mode suppression ratio ∼20 dB is obtained for proposed devices from threshold to rollover currents at all measure temperatures, with the peak output power of ∼30 mW at 10 K in pulsed mode and lateral divergence angle reduced by half. The proposed devices are good candidates for high-power, single-mode operation and low-divergence laser with easy fabrication.