  Microscopic features of carrier localization, minibands, and spectral
currents of InAs/GaSb based type-II superlattice (T2SL) mid-infrared detector
structures are studied and investigated in detail. In the presence of momentum
and phase-relaxed elastic scattering processes, we show that a self-consistent
non-equilibrium Green's function method within the effective mass approximation
can be an effective tool to fairly predict the miniband and spectral transport
properties and their dependence on the design parameters such as layer
thickness, superlattice periods, temperature, and built-in potential. To
benchmark this model, we first evaluate the band properties of an infinite T2SL
with periodic boundary conditions, employing the envelope function
approximation with a finite-difference discretization within the perturbative
eight-band $\bf{k.p}$ framework. The strong dependence of the constituent
material layer thicknesses on the band-edge positions and effective masses
offers a primary guideline to design performance-specific detectors for a wide
range of operations. Moving forward, we demonstrate that using a finite T2SL
structure in the Green's function framework, one can estimate the bandgap,
band-offsets, density of states, and spatial overlap which comply well with the
$\bf{k.p}$ results and the experimental data. Finally, the superiority of this
method is illustrated via a reasonable estimation of the band alignments in
barrier-based multi-color non-periodic complex T2SL structures. This study,
therefore, provides deep physical insights into the carrier confinements in
broken-gap heterostructures and sets a perfect stage to perform transport
calculations in a full-quantum picture.
