We demonstrate simultaneous lasing at two well-separated wavelengths in self-assembled InAs quantum-dot lasers, via ground-state (GS) and excited-state (ES) transitions. This effect is reproducible and strongly depends on the cavity length. By a master-equation model, we attribute it to incomplete clamping of the ES population at the GS threshold.

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In this paper, we present a systematic study of the effect of growth parameters on the structural and optical properties of InAs quantum dot ͑QD͒ grown under Stranski-Krastanov mode by molecular beam epitaxy. The dot density is significantly reduced from 1.9ϫ10 10 to 0.6ϫ10 10 cm Ϫ2 as the growth rate decreases from 0.075 to 0.019 ML/s, while the island size becomes larger. Correspondingly, the emission wavelength shifts to the longer side. By increasing the indium fraction in the InGaAs capping layer, the emission wavelength increases further. At indium fraction of 0.3, a ground state transition wavelength as long as 1.4 m with the excited state transition wavelength of around 1.3 m has been achieved in our dots. The optical properties of QDs with a ground state transition wavelength of 1.3 m but with different growth techniques were compared. The QDs grown with higher rate and embedded by InGaAs have a higher intensity saturation level from excitation dependent photoluminescence measurements and a smaller intensity decrease from temperature dependent measurements. Finally, single mirror light emitting diodes with a QD embedded in InGaAs have been fabricated. The quantum efficiency at room temperature is 1.3%, corresponding to a radiative efficiency of 21.5%.

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