Interface trap-induced dark current in graded-layer long-wavelength infrared HgCdTe nBn photodetector

Abstract

Long-wavelength infrared (LWIR) mercury cadmium telluride (HgCdTe) nBn photodetectors are highly promising for low dark current. Introducing Cd composition and doping concentration graded-layers effectively optimizes band alignment and carrier distribution, enhancing optoelectronic performance. However, these graded-layers generate unique interface traps that differ from bulk traps, due to intrinsic trap properties, strain relaxation and interdiffusion effects. This work specifically explores the dark current characteristics of the graded-layer LWIR HgCdTe nBn photodetector using simulation tools, achieving strong agreement with experimental results. Results confirm that interface traps are the dominant contributors to dark current, surpassing conventional Shockley-Read-Hall (SRH), Auger, and radiative recombination mechanisms. Their contribution to dark current is 1–2 orders of magnitude higher than that from bulk traps. These interface traps include acceptor-like traps located approximately 0.025 eV below the conduction band and donor-like traps around 0.25 eV above the valence band, primarily modulating interfacial charge density and electric fields through carrier capture and release processes rather than direct generation-recombination (G-R) effects. Notably, interface traps, particularly those at the absorber-barrier interface, are directly responsible for the observed negative differential resistance effect within 0.1–0.2 V reverse bias. This phenomenon is attributed to Fermi level shifts that lead to asynchronous ionization of charged traps. These effects persist with the similar order of photocurrent under infrared illumination, further highlighting their critical role. This work offers new insights into the role of interface traps in LWIR HgCdTe nBn photodetectors, offering guidance for optimizing their performance.