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This paper presents the lasing properties and their temperature dependence for 1.3-/spl mu/m semiconductor lasers involving self-assembled InGaAs-GaAs quantum dots as the active region. High-density 1.3-/spl mu/m emission dots were successfully grown by the combination of low-rate growth and InGaAs-layer overgrowth using molecular beam epitaxy. 1.3-/spl mu/m ground-level CW lasing occurring at a low threshold current of 5.4 mA at 25/spl deg/C with a realistic cavity length of 300 /spl mu/m and high-reflectivity coatings on both facets. The internal loss of the lasers was evaluated to be about 1.2 cm/sup -1/ from the inclination of the plots between the external quantum efficiency and the cavity length. The ground-level modal gain per dot layer was evaluated to be 1.0 cm/sup -1/, which closely agreed with the calculation taking into account the dot density, inhomogeneous broadening, and homogeneous broadening. The characteristic temperature of threshold currents T/sub 0/ was found to depend on cavity length and the number of dot layers in the active region of the lasers. A T/sub 0/ of 82 K was obtained near room temperature, and spontaneous emission intensity as a function of injection current indicated that the nonradiative channel degraded the temperature characteristics. A low-temperature study suggested that an infinite T/sub 0/ with a low threshold current (/spl sim/1 mA) is available if the nonradiative recombination process is eliminated. The investigation in this paper asserted that the improvement in surface density and radiative efficiency of quantum dots is a key to the evolution of 1.3-/spl mu/m quantum-dot lasers.