One more peculiarity of PbTe is the extreme high dielectric constant. The typical values of the dielectric constant range from 500 ... 1000 (depending on temperature and doping level). This is the reason why the subband level splitting is relatively small (approx. 3 meV for the oblique valleys and 1 meV for the longitudinal valley) and the potential wells are rather wide at the usual doping levels of 1-2x10^17 cm^-3. Consequently tunnelling between neighbouring nipi periods does not occur even if the amplitude of the nipi-potential is designed to be as low as 5meV (more about this fact can be seen from "Basic considerations of potential schemes in PbTe ")
The result of the model calculation of a typical nipi potential is shown in figure 2 below. In addition to the subband separation also the weak penetration of the wave functions into the potential barriers as compared to the width of the barriers can be seen.
Fig.2: left: wave functions for electrons of in the longitudinal valley, right: wave functions of electrons in the oblique valleys, the bulk doping level is 1x10^17cm^-3 for p- and n- layers.