In0.145Ga0.855AsySb1−y semiconductor alloys were grown on GaSb(100) substrates by varying the As content by liquid phase epitaxy (LPE). We demonstrated that the growth mechanism of these quaternary alloys is mainly constituted by two stable bonding configurations, Ga−Sb and In−As. These quaternary alloys showed a high crystalline quality due to the nearly lattice-matched epitaxial growth to the GaSb substrate. We identified a tensile strain of the In0.145Ga0.855AsySb1−y alloys on the GaSb substrate, strain that increases with the As content. In the bulk region of these crystalline alloys it was noticed a greater fonon-plasmon coupling than in the surface space-charge region. In addition, we found that the band gap energy of the In0.145Ga0.855AsySb1−y alloys can be easily engineered in the near infrared by varying the As content. Excitonic transitions were observed in these quaternary alloys, whose energy decreases with the As content. We employed a theoretical method that considers spin-orbit coupling for the determination of the band gap energy, which is in agreement with experimental results. These findings provide an important understanding of the growth dynamics, and of the optical and structural properties of the In0.145Ga0.855AsySb1−y crystalline alloys by varying the As content for near infrared applications using the band gap engineering. Display omitted •In0.145Ga0.855AsySb1−y alloys were grown on GaSb substrate by varying the As content.•The quaternary alloys were grown by Liquid Phase Epitaxy (LPE).•The growth mechanism of these alloys is mainly constituted by Ga−Sb and In−As.•The excitonic transition energies of the alloys decrease with the As content.