Most narrow bandgap semiconductors have complex band structures with multiple bands near the conduction/valence band edge. The charge transport in these materials has a contribution from multiple bands which needs to be accounted for during modelling. Typically this is done by taking the summed contribution of individual bands which are treated as parabolic. This is however not an accurate description in semiconductors with multiple degenerate bands at the same k-point . To overcome this problem the interband scattering parameter needs to be included in the calculation.