Improved performance from GaAs–AlGaAs quantum cascade lasers with enhanced upper laser level confinement

We present a comparison of the lasing characteristics for two nearly identical GaAs–AlGaAs quantum cascade lasers with an optimised InGaAs–AlInAs device operating at a similar wavelength. The effects on the laser performance resulting from modifications to the upper lasing state lifetime and optical transition matrix element for the GaAs–AlGaAs devices are investigated by selectively altering the aluminium composition of a single barrier within the active region. The sample containing an Al0.4Ga0.6As barrier exhibits a lower-threshold current density (3.75 kA/cm2) and increased slope efficiency (280 mW/A) at 10 K relative to the sample with an Al0.33Ga0.67As barrier, consistent with calculations.