Effect of active-region modulation doping on simultaneous ground-state and excited-state lasing in quantum-dot lasers

The lasing spectra and light-power characteristics of lasers based on InAs/InGaAs quantum dots with $p$-type modulation doping are studied over a broad range of pump currents. It is shown that $p$-type doping leads to a significant increase in the threshold current for the onset of lasing at the excited-state transition and makes it possible to attain higher output powers for lasing at the ground-state transition as compared to lasers with an undoped active region. An explanation for the observed features of two-level oscillation in quantum-dot lasers is suggested.