Optical characterization has been performed on the InAs/InP surface layer in order to study the arsenic (As) stabilization process of InP. The InAs layers are formed by the simple exchange of phosphorus (P) from the InP surface substrate by arsenic. Samples prepared under arsenic overpressure in the temperature range 450-600-degrees-C have been examined. Luminescence from the InAs layer which acts as a surface quantum well has been detected. We have compared this emission with theoretical calculations and reasonable agreement was observed. Moreover, we have determined that when the arsenic stabilization temperature increases the InAs thickness increases as a consequence of P-As exchange and that after the replacement of the five first top monolayers this exchange seems to stop. We explain this result in terms of the shield effect of the InAs overlayers which efficiently cap the InP substrate against further P evaporation and the restoration of surface structural order which limits any other phosphorus exodiffusion. Comparing our results with those of x-ray photoelectron spectroscopy measurements we have concluded that on samples treated at high temperatures, three-dimensional InAs islands are formed.