Low field electron transport in a GaAs/GaAlAs superlattice

This thesis presents some results of low field mobility and Hall factor calculations in a GaAs/Gao.7Alo.3As superlattice. There is much experimental evidence that for a superlattice with a large enough miniband width, the electron transport proceeds by extended Bloch states and consequently the Boltzmann transport formalism is used. For these calculations polar optical phonon scattering and interface roughness scattering are considered. Early calculations assumed the vibrational modes of a superlattice to be unperturbed by the superlattice structure. However the optical vibrational modes of a thin layer structure deviate strongly from those of the corresponding bulk materials. This effect is included in these calculations by using the dielectric continuum model and is found to increase the predicted mobility by up to a factor of two. This predicted polar optical phonon limited mobility is however, much larger than the experimentally measured mobility. By including interface roughness scattering agreement with experiment is significantly improved. For a superlattice grown without growth interruptions at the interfaces the interface roughness scattering dominates electron transport in the growth direction and is of similar importance to polar optical phonon scattering for transport parallel to the layers. The effect of growth interruptions is investigated and is found to reduce interface roughness scattering. Finally the Hall factors are calculated, the superlattice has two independent Hall factors both of which remain close to one