Quantum efficiency enhancement using photon-trapping structure on extended SWIR type-II superlattice nBn photodetector

Type-II superlattice (T2SL) material systems are emerging as promising alternatives to conventional materials such as InGaAs and HgCdTe for extended short-wavelength infrared (eSWIR) detection, a field experiencing growing demand due to its diverse applications. However, T2SL photodetectors typically suffer from relatively low quantum efficiency. In this study, we demonstrate a significant enhancement in the quantum efficiency of eSWIR T2SL photodetectors through the implementation of a photon-trapping structure. The photon-trapping structure, consisting of top diffraction gratings and a bottom reflective metal layer incorporated via wafer bonding, effectively increases the optical path length within the active region by redirecting incident light to propagate laterally. Optical measurements demonstrate a 77.2% improvement in average quantum efficiency for the photon-trapping photodetector compared to a conventional reference photodetector over the 1.7 μm to 2.5 μm wavelength range. Finite-difference time-domain (FDTD) simulations of electric field distributions and optical resonance analyses reveal that this enhancement is driven by the combined effects of Fabry-Perot resonances and multiple guided-mode resonances, arising from the synergy between the bottom reflective metal and the diffraction grating.