In this work, we present our approach towards the growth of active regions and cladding layers for GaSb based record low-threshold lasers emitting in the range of 2.5-2.7 mu m. First, a study on Sb incorporation in the AlGaAsSb cladding layers and GalnAsSb QWs is presented as a function of growth temperature. A linear decrease in Sb incorporation was observed for both cases. Second, a choice of well-barrier material is presented. Here, the best results have been achieved with a GaSb/GalnAsSb combination, yielding a low-temperature (20 K) photoluminescence (PL) response with a very narrow full-width at half-maximum (FWHM) of 4.5 meV. The latter is followed by an investigation of active region degradation with increased annealing temperatures. The rapid degradation has been confirmed by PL and X-ray diffraction studies. Finally, device results are presented. Lasers show ultra-low CW threshold current densities (44 A/cm(2) at L -> infinity), in the wavelength range of 2.5-2.7 mu m. (C) 2010 Elsevier B.V. All rights reserved.