Red Light Emitting Injection Lasers with Vertically-Aligned InP/GaInP Quantum Dots

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Abstract
In this paper, we demonstrate the first injection lasers, using threefold-stacked vertically-aligned InP/GaInP quantum dots (QD's) as the active medium. The lasers emit in the visible part of the spectrum (690–710 nm) with a threshold current density (j th) of 172 A/cm2 at 90 K, increasing with temperature up to j th = 685 A/cm2 at 210 K. We identify the lasing being due to QD ground state transitions. The temperature dependence of j th is investigated in detail. At low temperatures, the threshold current density is almost independent of temperature while, towards higher temperatures, a thermally activated increase is found, strongly depending on QD size. The rise in j th is accompanied by a decrease of the integrated photoluminescence (PL) intensity, indicating that nonradiative recombination of carriers plays a significant role with increasing temperature. We assume thermal evaporation of carriers out of the dots and into the wetting layer (WL), where they recombine nonradiatively, to be the process responsible for the increase in j th.