ELECTRONIC-STRUCTURE OF N-TYPE DELTA-DOPING MULTIPLE LAYERS AND SUPERLATTICES IN SILICON

The electronic subband structure of periodically n-type delta-doped silicon is calculated self-consistently within the local-density approximation. Two types of energy levels are distinguished, one due to valleys transverse to the superlattice axis, and the other due to longitudinal valleys. Minibands, potential profiles, miniband occupancies, and Fermi-level positions are studied and their dependence on the spacing d between delta layers and the doping concentration ND is obtained. Pronounced changes with increasing N-D and decreasing d are observed. For d > 150 Angstrom, and 10(13) less than or equal to N-D < 10(15) cm(-2), the system behaves as a set of practically independent isolated delta-doped wells, Significant dispersion of the higher subbands takes place for d lower than 150 Angstrom. The transition from a multiple-delta-doped-well behavior to a superlattice regime is observed for doping concentrations > 2.0 x 10(13) cm(-2) and periods d < 50 Angstrom. The twofold degeneracy of longitudinal levels and the fourfold degeneracy of tranverse levels are removed by the many-valley coupling. The corresponding splitting energies are calculated.