The optical and transport properties of In0.52Alo.48As grown by molecular beam epitaxy have been studied as a function of growth temperature in the range of 300-520° C. It is evident that under our growth conditions, thermodynamic considerations become important, and combined with surface kinetics, clustering effects become most severe for growth temperatures around 400° C. The clustering effects are manifested by changes in low-temperature photoluminescence, Hall transport and in the properties of Schottky diodes made on the films and the relevant parameters show a peaking for growth at 400° C. In particular, the Hall mobility exhibits a turning point forT > 300 K, beyond which the mobility increases with increasing temperature. In addition, the Hall electron concentration exhibits an anomalous reduction in value in the same high-temperature range. Measurements were also made on In0.52Al0.48As grown at 620-650° C by metalorganic chemical vapor deposition. While these films exhibit the same turning point in Hall mobility, the reduction in carrier concentration is significantly absent. Analysis of these data therefore indicates that the turning point in the mobility, which is present for both growth techniques, is caused by small clusters (~35Å) of phases slightly different from the mean composition. The reduction in electron concentration, seen only in the molecular beam epitaxial samples, suggest a more severe phase separation. A simple analysis for the sample grown at 400° C indicates that the compositions In0.60Al0.40As and In0.44Al0.56As might be present, in addition to the mean lattice-matched composition.