Band gap modification in Ne+-ion implanted In1−xGaxAs/InP (x=0.25, 0.33, 0.40, 0.47, 0.54, 0.61, 0.69) and InAsyP1−y/InP (y=0.32) quantum well structures has been studied by low temperature (12 K) photoluminescence spectra. The maximum usable high temperature anneal for inducing the compositional intermixing using an InP proximity cap is found to be ∼700 °C for 13 s. A second low-temperature (300 °C) anneal, following the high-temperature (700 °C) anneal, is found to induce greater band gap changes than the simple one-step anneal at 700 °C. The changes are found to be approximately proportional to the difference of bandgap energy between the well and the barrier materials; the proportionality coefficient increases with ion dose and reaches a maximum at a dose of ∼2×1013 cm−2. At higher doses, the proportionality coefficient decreases. The band gap changes are explained qualitatively based on the InGaAsP binary composition diagram.