In order to adjust the highly controllable and optimum growth conditions, the multi-step interrupted-growth MBE processes were performed to deposit a series of GaAs/Al_0.45Ga_0.55As QCL structures. The additional calibrations of MBE system were carried out during the designed growth interruptions. This solution was combined with a relatively low growth rate of active region layers, in order to suppress the negative effects of elemental flux instabilities. As a result, the fabricated QCL structures have yielded devices operating with peak optical power of ∼12 mW at room temperature. That is a better result than was obtained for comparable structures deposited with a growth rate kept constant, and with the only initial calibrations performed just before the epitaxy of the overall structure.