Dark current modeling of MWIR type-II superlattice detectors

We report on temperature dependence characteristics of medium wavelength InAs/GaSb type-II superlattice p-i-n and nBn photodetectors in a temperature range from 77 K to 300 K. A bulk based model with an effective band gap of superlattice material has been used in modeling of the experimental data. Temperature dependence and bias dependent dark current and dynamic resistance of the devices have been analyzed in detail to investigate contributing mechanisms that limit the electrical performance of the detectors. The I-V and RA(V) characteristics of both types of detectors (p-i-n and nBn structures) are dominated by diffusion and generation-recombination currents in the zero-bias and the low-bias regions. At medium values of reverse bias, the dark current is mostly due to trap-assisted tunneling. At high values of reverse bias, the bulk band-to-band tunneling dominates. A good fitting of theoretical predictions with experimental data in a wide range of bias voltages and temperatures has been possible assuming that the position of trap-assisted tunneling level depends on temperature. The temperature dependence of trap level position can be explained by its less sensitivity on temperature changes in comparison with superlattice miniband edges. Between room temperature and 200 K the generation-recombination component and the diffusion component of carrier lifetimes are similar and have shown values about 2-10 ns. At a lower temperature the diffusion lifetime is longer and increases to about 100 ns for p-i-n structures.