Theoretical aspects of electron transport in modulated structures

In the theory of transport in modulated structures, both transport perpendicular and parallel to the heterojunction interfaces were studied. In perpendicular transport models were investigated for tunneling through double barriers and it was found that resonant tunneling and sequential tunneling lead to the same expression for the current as long as the width of the energy distribution of the injected electrons are larger than the width of the resonant level in the diode. Results are presented for phonon assisted tunneling between two wells in a model which remains valid even when the barrier shrinks and the tunneling probability becomes very high. Proposals for practical schemes for incorporating this model in programs for calculating the transport in generalized band-engineered structures are given. In parallel transport it was shown that very satisfactory agreement with extensive measurements of the mobility in modulation doped structures in the whole temperature range from 4 to 300 K can be obtained if the complete quasi-two-dimensional subband structure and all the relevant scattering mechanisms are taken into account. Having established this, the program is applied to systems with more complicated double channel structures, and it is shown how the conductivity of a channel in which perpendicular resonant tunneling affects parallel transport can be tailored.