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We examined the current–output power characteristics and light emission spectra for columnar-shaped self-assembled InGaAs quantum-dot lasers with a room temperature lasing threshold of 6 mA. Lasing threshold currents became obscure as temperature decreased below 180 K. While lasing occurred with one line including a series of longitudinal modes at room temperature, spectra at 80 K showed broad lasing emission over a range of 50–60 meV. We conclude that dots with different energies start lasing independently at low temperatures due to their spatial localization, while at room temperature the dots contribute to one-line lasing collectively via homogeneous broadening of optical gain.

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