In the present paper we discuss the electronic properties of semiconductor hetero junctions, focussing on the band offset problem. We address interface-specific phenomena, where the conditions of growth-including controlled contamination and strain effects-may significantly alter the properties of the junction. We study the effects of ultrathin intralayers (i.e. heterovalen-t implantation) both at homojunctions (such as GaAs/Ge/GaAs) and heterojunctions (such as GaAs/Si/AlAs). In both cases, our theory demonstrates how the intralayers control the band offset: this result is confirmed by recent experimental observation in several systems. We then consider the band-offset engineering at lattice-mismatched heterojunctions, studying the paradigmatic case GaAs/Si. We evaluate the band-offset for several fully relaxed inequivalent interfaces. Both macroscopic strain and microscopic morphology effects are considered.
