High Efficiency Injectorless Quantum Cascade Lasers Emitting at 8.8 $\mu$ m With 2-W Peak Pulsed Power per Facet at Room Temperature

An injectorless quantum cascade laser design using four material alloys and emitting around 8.8 at room temperature is presented. The coupling energy between the injection state and the upper laser level was increased compared to other injectorless designs to 10.6 meV. Devices with 85 repeats produce 2.0 W of pulsed output power per facet and an overall efficiency of 7.2% at 300 K. The threshold current density at room temperature is as low as 1.15 for an as-cleaved 4-mm-long device, with a characteristic temperature of 162 K.