Growth of In0.52Al0.48As epilayers on InP(100) substrates by molecular beam epitaxy at a wide range of substrate temperatures (470-550 degrees C) and at arsenic beam equivalent pressures which are higher than previously reported (D.F. Welch et al,, Appl. Phys. Lett., 46 (1985) 169), is carried out. A strong dependence of the photoluminescence (PL) and X-ray diffraction (XRD) linewidths and XRD intensity ratio (Int(epi)/Int(sub)) on the substrate temperature was observed. The lattice mismatch was the lowest when the growth was carried out at substrate temperatures of 500-520 degrees C. The XRD diffraction peaks of samples grown at low temperatures are comprised of smaller peaks suggesting an effect of disordering owing to the presence of alloy clustering. PL linewidth as low as 14 meV was recorded in samples grown at a V/III flux ratio as high as 160. The lattice mismatch in samples grown at high flux ratios was found to be insensitive to changes in the V/III flux ratios.