Role of thermal hopping and homogeneous broadening on the spectral characteristics of quantum dot lasers

The effect of thermal hopping and homogeneous broadening on the lasing spectra and carrier distribution in quantum dot lasers is investigated by measuring the spontaneous emission spectra through a top-contact window. Two intriguing features are observed, i.e., a strong redshift of the excited-state lasing peak as compared to the spontaneous emission spectrum and the absence of population clamping at threshold. These features are interpreted on the basis of a rate-equation model taking into account energy-broadening mechanisms and thermal coupling among quantum dots. The good agreement between model and experiment allows us to estimate the homogeneous broadening and capture time, two key parameters for the understanding and proper design of quantum dot lasers.