The band structure and density of states for large superlattices of (100) Ga-site Ge and As-site N impurity sheets in GaAs have been calculated by a semiempirical tight-binding technique. Both of these two-dimensional conduction-band derived bands with a J-point indirect minimum which is deep in energy (∠0.5 eV) relative to the bulk conduction band edge. The calculation, which was performed on a single impurity sheet, demonstrates that, in general, a planar defect localizes or binds one or more states. It is suggested that the large binding energies of these sheets will confine electric-field-accelerated carriers and thus such superlattices will be highly conductive parallel to the impurity sheets.