We report on critical ion implantation and rapid thermal annealing (RTA) process temperatures that produce resistive Fe- or Ga-implanted InGaAsP/InP heterostructures. Two InGaAsP/InP heterostructure compositions, with band gap wavelengths of 1.3 lm and 1.57 lm, were processed by ion implantation sequences done at multiple MeV energies and high ﬂuence (1015 cm-2). The optimization of the fabrica- tion process was closely related to the implantation temperature which inﬂuences the type of implant-induced defect structures. With hot implantation temperatures, at 373 K and 473 K, X-ray diffraction (XRD) revealed that dynamic defect annealing was strong and prevented the amorphization of the InGaAsP layers. These hot-implanted layers were less resistive and RTA could not optimize them systematically in favor of high resistivity. With cold implantation temperatures, at 83 K and even at 300 K, dynamic annealing was minimized. Damage clusters could form and accumulate to produce resis- tive amorphous-like structures. After recrystallization by RTA, polycrystalline signatures were found on every low-temperature Fe- and Ga-implanted structures. For both ion species, electrical parameters evolved similarly against annealing temperatures, and resistive structures were produced near 500 °C. However, better isolation was obtained with Fe implantation. Differences in sheet resistivities between the two alloy compositions were less than band gap-related effects. These observations, related to damage accumulation and recovery mechanisms, have important implications for the realization ion-implanted resistive layers that can be triggered with near infrared laser pulses and suitable for ultrafast optoelectronics.