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• Optical spectroscopy tools give access to details of the optical properties and crystal quality of high-x In x Ga 1-x As layer. • The high-x In x Ga 1-x As/InP structures with low Indium concentration will exhibit excellent PL and structural properties. • Low-temperature (10 K) time-resolved PL measurements show the increase of lifetime with increasing the indium concentration. • Abnormal behavior of the luminescence keys has been observed. Optical and structural properties in high-x In x Ga 1-x As (x > 0.65) samples with varying indium concentration grown on InP (1 0 0) substrate are reported. By increasing the indium fraction, it was found by the high-resolution X-ray diffraction (HR-XRD) study that the dislocation density in the In x Ga 1-x As epitaxial layer significantly increased, and the surface quality deteriorated remarkably. Photoreflectance (PR) spectra show the presence of Franz-Keldysh Oscillations (FKOs) features above the In x Ga 1-x As energy bandgap. The strain-induced electric field is then estimated directly from the FKOs periods. Temperature-dependent photoluminescence (TDPL) measurements from 10 K to 300 K showed carrier locations (S-shape). This abnormal behavior is due to the dislocation density associated with fluctuations in the indium concentration. A quasi-stationary rate equation model for the temperature-dependent luminescence spectra of the localized state material system is proposed to interpret the band gap emission process quantitatively. Low-temperature (10 K) time-resolved PL measurements show the increase of lifetime with increasing the indium concentration. Yet, the addition of only 1.7% of indium concentration results in a strong enhancement of PL lifetime by ∼ 80%. All these results reveal a more precise picture of the localization and recombination mechanisms of photogenerated carriers in the InGaAs layer, which could be the crucial factors in controlling the performance of high indium content InGaAs SWIR detector. [ABSTRACT FROM AUTHOR]