Carbon ion bombardment in the energy range of 20–500 eV, which occurs in reactive ion etching using alkanes, has been performed on InP with a mass‐separated carbon ion beam in an ultrahigh vacuum chamber. The sample structure consisted of an ultrathin, epitaxial InP (40 A˚) layer on InGaAs.Insitupolar‐angle dependent x‐ray photoelectron spectroscopy was used to measure sputtering, deposition on, and damage of the InP layer, and to determine if any damage had propagated to the underlying InGaAs. An investigation of damage removal was also carried out byinsituthermal annealing, and by exposure to ultraviolet radiation and ozone. It was found that carbon ion bombardment led to carbon incorporation and to a gross change in the surface composition of the semiconductor. A complex, heterogeneous In‐P‐C alloy was formed. Sputtering of InP and preferential removal of P were also evident. Further carbon ion bombardment resulted in the deposition of an amorphous carbon residue. The degree of residual damage increased with bombarding energies. At 20 eV, the damage was confined to the 40 A˚ InP layer, but at 100 eV, significant broadening of the As 3dpeak was observed, which suggests that the underlying InGaAs layer was also damaged at this higher energy. Bombardment with 500 eV ions caused severe damage to both the InP and InGaAs layers. Heating of the irradiated samples at 350 °C in vacuum was ineffective in annealing the damage, although a reduction of the surface Fermi level position from 0.95 to 0.75 eV (relative to the valence band maximum) was measured for 20 eV carbon ion bombarded samples. This is attributed to the acceptor behavior of the incorporated carbon. Exposure to ultraviolet light/ozone was also found to be ineffective in removing the carbon residue.