Lasing characteristics of self-formed quantum-dot lasers with multistacked dot layer

Room-temperature continuous-wave (CW) operation at the ground state has been achieved in self-formed quantum-dot lasers with multistacked dot layer. By systematic investigation, discontinuous shifts of lasing wavelength from the high-order subbands to the ground state are clearly demonstrated for the first time by varying the number of dot layers and the cavity loss. Lasers oscillating at different subbands exhibit different behaviors against temperature both in the spectral characteristics and in the threshold currents, which are strongly related to emission efficiency of quantum dots and thermal excitation of carriers to higher order subbands. High characteristic temperature over 300 K has been achieved in a laser with high-reflection coating on both facets in the temperature range 60-200 K. Future prospects of improvement in the laser characteristics are also discussed.