Improvement of λ≈5 μm quantum cascade lasers by blocking barriers in the active regions

We report the improvement of quantum cascade lasers emitting at $\text{λ∼5\hspace{0.17em}μ}\mathrm{m}$ by introducing AlAs blocking barriers together with strain-compensating InAs layers into the active regions. The blocking barriers are designed to selectively prevent electrons in the initial laser state from tunneling out of the active region, while maintaining the high tunneling probabilities of the electrons in the final laser states. Adopting blocking barriers, the maximum peak power per facet at 77 K (300 K) is increased from 285 (30 mW) to 900 mW (240 mW), and the maximum operation temperature in pulsed mode has been improved from 320 to 350 K with respect to a reference sample without blocking barriers.