Growth of In 0 . 5 2 Al 0 . 4 8 As epitaxial layers on InP(100) substrates by molecular beam epitaxy at a wide range of arsenic overpressure (V/III flux ratio from 30 to 300) is carried out. Analysis performed using low-temperature photoluminescence (PL) and double-axis X-ray diffraction (XRD) showed a strong and prominent dependence of the PL and XRD linewidths on the V/III flux ratio. Under our growth conditions, both the PL and XRD linewidths exhibit a minimum point at a V/III flux ratio of 150 which corresponds to a maximum in the PL intensity and XRD intensity ratio. Flux ratios exceeding 150 results in an increase in both the PL and XRD linewidths corresponding to a reduction in their associated intensities. Room temperature Raman scattering measurements show a narrowing in the InAs-like and AlAs-like longitudinal-optic (LO) phonon linewidths which broaden at high flux ratios, while the LO phonon frequencies exhibit a gradual reduction as the flux ratio is increased. PL spectrum taken at increasing temperature show a quenching of the main emission peak followed by the evolution of a broad lower energy emission which is possibly associated with deep lying centres. This effect is more prominent in samples growth at lower V/III flux ratios.