摘要： Terahertz (THz) quantum cascade lasers (QCLs) are powerful coherent light sources covering the frequency range from 1.2 to 5.4 THz, but still suffer from operation temperatures below 200 K. Here, we show the results of a barrier height study for a three-well active region based on GaAs/AlxGa1-xAs heterostructure with changing Al concentrations from x = 12% to 24%. Higher barriers reduce the thermal leakage of electrons at elevated temperatures and reduce the coupling of the electron wave functions. The calculated energy difference of these two electronic states (1.75 meV) agrees with the separation of the two regions in the measured frequency spectrum at 3.4 and 3.8 THz (ΔE = 1.65 meV) at low temperature. With this technique we expect to improve the maximum operation temperature and to optimize broadband devices which are necessary for frequency combs and mode-locked devices.