We have used photoexcitation-dependent radiative efficiency measurements to investigate the rates of defect-related, radiative, and Auger recombination in lattice-matched In x Ga 1Ϫx As/InAs y P 1Ϫy double heterostructures on InP substrates. Temperature dependence is used to discern the underlying mechanisms responsible for the nonradiative recombination processes. We find that defect-related recombination decreases with an increase in the temperature when the epistructure is lattice matched to the substrate (xϭ0.53). In contrast, when the epistructure is lattice mismatched to the substrate, defect-related recombination increases slowly with the temperature. The difference between the lattice-matched and mismatched cases is related to fundamental changes in the defect-related density of states function. The temperature dependence in the lattice-mismatched structures is attributed to two competing effects: wider carrier diffusion, which augments the capture rate, and thermally activated escape, which reduces the occupation of shallow traps. The band gap and temperature dependence of the Auger rate demonstrate that the conduction to heavy hole band/ splitoff to heavy hole band mechanism generally dominates Auger recombination in undoped low-band gap In x Ga 1Ϫx As. With this interpretation, our results give a spin-orbit valence split-off band effective mass of m so ϭ(0.12Ϯ0.02)m 0 .