86% internal differential efficiency from 8 to 9 µm-emitting, step-taper active-region quantum cascade lasers.

8.4 μm-emitting quantum cascade lasers (QCLs) have been designed to have, right from threshold, both carrier-leakage suppression and miniband-like carrier extraction. The slope-efficiency characteristic temperature T, the signature of carrier-leakage suppression, is found to be 665 K.