We demonstrate the first 1.3-μm continuous-wave (CW) lasing at room temperature of self-assembled InGaAs-GaAs quantum dots. High-density 1.3-μm emission dots were successfully formed by the combination of low-rate growth and InGaAs-layer overgrowth methods of molecular beam epitaxy. The 1.3-μm ground-level CW lasing occurred at up to 40/spl deg/C, and the threshold current of 8 mA at 25/spl deg/C is less than one thirtieth of values ever reported for 1.3-μm dot pulse lasers. The achievement represents a milestone for creating quantum-dot lasers applicable to fiber-optic communication system.

The effect of phonon bottleneck on quantum-dot laser performance is examined by solving the carrier-photon rate equations including the carrier relaxation process into the quantum-dot ground state. We show that the retarded carrier relaxation due to phonon bottleneck degrades the threshold current and the external quantum efficiency. We also show that quantum-dot lasers are quite sensitive to the crystal quality outside as well as inside quantum dots. Our results clarified that the relaxation lifetime should be less than about 10 ps to fully utilize the laser potential originating from the quantum-dot discrete energy states.

We studied the excitation-power dependence of photoluminescence (PL) spectra and the current dependence of electroluminescence (EL) spectra of self-formed InGaAs/GaAs quantum dots. We observed five peaks in the PL and EL spectra. From the size dependence of the peak interval and the carrier-density dependence of peak energy and peak intensity, we assigned the peaks to the discrete energy levels in the quantum dots. We simulated the EL spectra with rate equations, taking into account the carrier relaxation between the discrete levels, and found that the relaxation lifetime was about 10–100 ps.

A laser oscillation from self-organized In/sub 0.5/Ga/sub 0.5/As quantum dots is achieved at 80 K by current injection. Lasing at a three-dimensionally quantum confined sublevel of the In/sub 0.5/Ga/sub 0.5/As quantum dots is clearly demonstrated for the first time by electroluminescence and diamagnetic energy shift measurement. The results predict the possibility of ultra-low threshold current operation of quantum dot lasers.

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.