Reflection anisotropy spectroscopy (RAS) and reflection high-energy electron diffraction (RHEED) were applied to study clean InP(001) surfaces prepared by molecular beam epitaxy (MBE). At phosphorus beam equivalent pressures (BEPs) between3.5×10−7and3.5×10−6mbar and substrate temperature(Ts)falling from 590 to 150 °C, (2×4), (2×1), (2×2), andc(4×4)RHEED patterns are observed. The main RAS features, observed at 1.7–1.9 and 2.6–2.9 eV are assigned to In and P dimers, respectively. The above reconstruction sequence is associated closely with transformations identified in RAS signatures that are induced by progressively increasing the P surface coverage. The RAS results also imply the existence of (2×4)&agr; and (2×4)&bgr; phases. A surface-phase diagram for MBE-grown (001) InP, in the whole range ofTsand phosphorus BEPs is proposed. ©1997 American Institute of Physics.