High-energy implantation of iron in n-type doped InP epilayers at different substrate temperatures: 77K, room temperature (RT), 100degreesC and 200degreesC was investigated to study the electrical isolation of n-type InP. Iron isolation implants were performed at 1MeV with a fluence of 5 x 10(14) /cm(2). This isolation scheme was chosen to place most of the iron atoms well inside the n-type doped layer. The sheet resistivity (R,), sheet carrier concentration (n(S)) and sheet mobility (p) were measured as a function of substrate temperature and post-implantation annealing temperature (100 - 800degreesC). Samples implanted at 77K, RT and 100degreesC show more or less the same trend of postimplant annealing characteristics. A maximum sheet resistivity of similar to1 x 10(7) Omega/rectangle was achieved for samples implanted at 77K, RT and 100degreesC after annealing at 400degreesC. A lower resistivity of similar to1 x 10(6) Omega/rectangle was obtained for a 200degreesC implant after annealing at 4000C. Lower damage accumulation due to enhanced dynamic annealing is observed for the highest implantation temperature. For 200degreesC substrate temperature, annealing above 4000C resulted in a gradual decrease in sheet resistivity to a value close to that of the starting material. But this is not the case for the lower substrate temperatures. The sheet resistivity was increased again for 77K, RT and 100()C implant after annealing at 600degreesC. We infer that for 77K, RT and 100degreesC implantation temperatures, the electrical isolation is due to a product of both damage related centers and defects related to the presence of Fe whereas for 200degreesC substrate temperature, we infer that only damage induced compensation removes the carriers. These results show the importance of iron implants as a device isolation scheme.