Electronic Properties of a Semiconductor Superlattice II. Low Temperature Mobility Perpendicular to the Superlattice

Low temperature mobilities parallel to the layers of a heavily doped n-type GaAs–Ga 1- x Al x As superlattice are calculated as a function of carrier concentrations. Assumed scattering mechanisms are Coulomb scattering from donor ions and surface roughness scattering at the interface. The subband structure in the presence of the band bending is calculated by the variational method. The surface roughness scattering is shown to be relatively unimportant and the Coulomb scattering is dominant. The mobility in the modulation doping case becomes nearly one order of magnitude larger than that in the uniform doping case in agreement with recent experiments. The band bending effect is important in the modulation doping case and reduce the mobility at large carrier concentrations. The intersubband scattering greatly reduces the mobility when electrons occupy higher subbands.