Quantum dot laser: gain spectrum inhomogeneous broadening and threshold current

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Abstract
Theoretical analysis of the gain and threshold current of a quantum dot (QD) laser is given taking into account the linewidth broadening caused by fluctuations in QD sizes. The following processes are taken into consideration together with the main process of the radiative recombination of carriers in QDs: the band-to-band radiative recombination of carriers in the waveguide region, carrier capture into QDs, and thermally excited escape from QDs. Expressions for the threshold current density depends on the root mean square of QD size relative fluctuations, surface density of QDs, thickness of the waveguide region, and total losses that have been obtained in an explicit form. The minimal threshold current density and optical values of the structure parameters are calculated as univeral functions of the main dimensionless parameter of the elaborated theory. This parameter is the ratio of the simulated transition rate in QDs to the spontaneous transition rate in the waveguide region. Theoretical estimations presented in the paper confirm the possibility of a significant reduction of the threshold currents of QD lasers as compared with conventional quantum well lasers.

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