Modal gain and lasing states in InAs/GaAs self-organized quantum dot lasers

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Abstract
Injection lasers with self-organized quantum dot ~QD! active regions are attracting considerable attention due to their potential for low threshold current density ( J th) and temperature insensitive J th devices. 1,2 However, due to their small size, the QDs occupy only a very small fraction of the total waveguide volume. Hence, even if their material gain is large, their resultant modal gain may be relatively small. 2 In this communication we describe a technique, based on nor- mal incidence photocurrent, to determine the magnitude and spectral form of the modal gain of a laser containing a single layer of InAs/GaAs self-organized QDs. This technique is shown to be a simple and convenient method for determining the gain and, in particular, for comparing the relative gain spectra of different active region designs. The maximum gain of the ground state transition is shown to have a rela- tively small value and the consequences for the laser charac- teristics are discussed. InAs self-organized QDs were grown by molecular beam epitaxy on a ~001! GaAs substrate at a temperature of