Quantum‐well photodetectors based on lattice‐matched InGaAs/GaAsSb heterostructures on InP are promising candidates for mid‐infrared detection. However, the dark current in these devices can be elevated by the presence of deep levels. In this work, both bulk and interfacial deep levels in MBE‐grown homojunctions and heterojunctions are studied experimentally using low‐frequency noise spectroscopy and random telegraph signal (RTS) characterization. Several bulk and interface‐related levels have been identified and characterized in terms of energy level, cross‐section and trap type. It is expected that these ongoing defect studies will enable the growth of the higher‐quality material and heterostructures needed for future‐generation mid‐IR detectors and devices. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)