The modulation of the potential barrier of an isotype heterojunction by the incorporation during epitaxial growth of thin, heavily doped n and p regions either side of the heterointerface has been investigated by computer modelling. The resulting device structure, known as a doping interface dipole or DID, was first proposed by Capasso and co-workers (1985) as a means of introducing a bias-dependent pseudo-band offset in heterojunction devices. The results presented here predict how this bias dependence varies with the doping dipole parameters and the material properties of the host heterojunction, chosen here to be a pseudomorphic Si_1-xGe_x/Si p-isotype heterojunction.