Abstract

A quantum cascade laser emitting at $\lambda \sim 8.5\mathrm{\mu m}$ based on the excited-state injection is presented. The operating voltage is reduced for a low-voltage defect in the excited-state design, compared with the conventional ground-state injection design. The threshold voltage and voltage defect are as low as 6.3 V and 54 mV for a 30-stage active region, respectively. Devices were fabricated through standard buried-heterostructure processing to decrease the heat accumulation. A continuous-wave optical power of 340 mW is obtained at 283 K with a threshold current density of $2.7\mathrm{kA}/{\mathrm{cm}}^2$. Such a design has the potential to further improve the wall plug efficiency for increased voltage efficiency.

© 2018 Optical Society of America

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