Impact of valence band offset on optical transitions and carrier dynamics in LWIR InAs/InAsSb nBn detectors.

This work investigates long-wavelength infrared (LWIR) nBn heterostructures based on InAs/InAsSb type-II superlattice (T2SL) absorbers with AlGaAsSb electron-barrier layers using photoluminescence (PL), spectral response, and photoconductivity decay (PD) measurements. The structures were designed with different valence band offsets (VBO) at the absorber/barrier interface, enabling analysis of their influence on optical transitions, carrier transport, and recombination processes. The results show that VBO strongly affects the optical response and recombination mechanisms of the structures. In particular, an additional low-energy PL transition appears in structures with a valence-band barrier. This feature is attributed to hole accumulation at the absorber/barrier interface and the associated band bending. In contrast, structures with near-zero VBO exhibit a single dominant transition, consistent with efficient hole transport across the interface. Spectral response measurements reveal reduced responsivity in structures with a valence-band barrier, indicating limited carrier extraction. This is supported by photoconductivity decay results, which show a reduction of the time constant from ∼10 ns to ∼3 ns, suggesting a transition from transport-limited to recombination-dominated behavior. The observed correlation between PL transitions, responsivity, and temporal response demonstrates that VBO engineering directly controls interface-related recombination processes and carrier transport in LWIR T2SL nBn detectors.