Electronic-properties of isocalent anf hetrovalent semiconductor interfaces

The problem of whether band offsets at semiconductor interfaces are determined by bulk properties of the constituents or substantially affected by interface phenomena is critically readdressed. In particular, the conditions under which band offsets depend or not on the interface orientation are examined. State-of-the-art pseudopotential calculations are performed in a supercell geometry for GaAs/AlAs and GaAs/Ge grown in different directions. A new approach to the calculation of band offsets at semiconductor heterojunctions is proposed, based on ab-initio linear-response theory. The offset is shown to be the sum of two terms, the first of which depends only on bulk properties and is therefore independent on interface orientation and abruptness. The second, which vanishes for isovalent and non polar heterojunctions, does depend on the details of the interface geometry, but can be calculated -once the geometry is known- from such simple quantities as the lattice parameters and dielectric constants of the two constituents. The linear-response results are compared to the supercell ones and to the experimental data.