We report in this letter the molecular beam epitaxial (MBE) growth of In(0.52)Ab(0.48)As on InP (100) substrates at very high arsenic overpressures and their characterisation using low temperature photoluminescence (PL) and X-ray diffraction (XRD). The effect of the high arsenic overpressures on the optical quality and lattice-mismatch in the In(0.52)Ab(0.48)As material were investigated. Within the range of the V/III flux ratios investigated (32-266), our results show for the first time that very high arsenic overpressures during MBE growth have no detrimental effect on the quality of the InAlAs, in contrast to the generally believed crystalline degradation due to the adverse effect on the cation surface mobilities. There is also an insignificant effect on the quality of the heterointerface as the lattice-mismatch was relatively insensitive to flux ratio variations within the range investigated. A significant improvement in the uniformity of the PL peak energy was also observed.