1.3-μm CW lasing characteristics of self-assembled InGaAs-GaAs quantum dots

This paper presents the lasing properties and their temperature dependence for 1.3-mu m semiconductor lasers involving self-assembled InGaAs-GaAs quantum dots as the active region. High-density 1.3-mu m emission dots were successfully grown by the combination of low-rate growth and InGaAs-laser overgrowth using molecular beam epitaxy, 1.3-mu m ground-level CW lasing occurring at a low threshold current of 5.4 mA at 25 OC with a realistic cavity length of 300 mu m and high-reflectivity coatings on both facets, The internal loss of the lasers was evaluated to be about 1.2 cm(-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(-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-O was found to depend on cavity length and the number of dot layers in the active region of the lasers, A To 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, with a low threshold current (similar to 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-mu m quantum-dot lasers.