High requirements set upon infrared photodetectors stimulate the development of both more sophisticated materials and device structures. An example of the former is type-II broken gap InAs/GaSb superlattice proposed for the first time by Esaki, which is promising for infrared sensing systems. Mainly, due to its electro-optical properties, especially absorption edge, which can be easily tunable by changing the thickness of InAs and/or GaSb layers constituting a single period of superlattice. Unfortunately due to their complex nature none of the commercially available software packages are able to properly simulate both heterostructures and devices based on this material system.

In this paper various numerical methods are combined to determine parameters of photodiodes as close to experimental ones as possible. At first, the tight binding algorithm in the sps* basis was implemented to calculate the energy dispersion as a function of the k vector. Spin-orbit coupling was then introduced, which allowed a significant improvement in precision of determined effective heavy and light hole masses. Additional excited s* state allowed for better adjustments of conduction band especially in the case of high symmetry points. Parameters obtained by this method were used as input data in further numerical analysis of type-II InAs/GaSb superlattice photodetectors.

Additionally analysis of dark current of a Barrier Infrared Detector (BIRD) type device was performed. Its diffusion and generation-recombination components were considered as well as band-to-band and trap-assisted tunneling ones. The former dominate in high temperature operating regime. The latter are directly related to narrow bandgap of absorber material and relatively high electric field across depletion region. Finally, a numerical model of dark current was discussed, and theoretical results were compared with those obtained from experiment. Uncertainties were addressed and possible directions of improvement proposed.

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