Due to the small subband splitting in PbTe nipi- or pnp- structures the Landau level splitting in general is much larger than the subband splitting even at low magnetic fields. Therefore the situation can be considered to be like in the figure below:
The density of states is represented by a 2D - Landau peak at the position of each subband-Landau level- energy. It turns out to be a good approximation to separate the magnetic and the electric quantization. In this case the total density of states can be easily calculated by using the energy spectrum which results from the superposition of the subband spectrum and the Landau level spectrum.