This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing. This article appeared in Journal of Applied Physics 109, 083104 (2011) and may be found at https://doi.org/10.1063/1.3574406.The parameters for reducing the threshold current density of InAs/InGaAsP/InP quantum-dot (QD) lasers suitable for high temperature operation are studied. The structures were grown using metalorganic vapor phase epitaxy. Increasing the number of QD layers leads to a substantial improvement of the optical confinement and a markedly reduced threshold per dot layer in broad area devices. A reduction of the spacer thickness between the QD layers was not found to significantly affect device characteristics. Depending upon the device length, an optimum number of QD layers was deduced. Based upon optimized QD stacks, buried-heterostructure lasers with a medium device length emitting at 1.5 μm were fabricated. Laterally single-mode devices show promising low threshold currents near 10 mA and good thermal stability with a characteristic temperature of 65 K up to 90 °C.DFG, 43659573, SFB 787: Halbleiter - Nanophotonik: Materialien, Modelle, Bauelement