Plateau behavior and the metal-insulator transition in δ-doping superlattices for transport along the growth direction

The electric conductivity σ of δ-doping superlattices (SL’s) along the growth direction is investigated theoretically at low electric fields and zero temperature. A plateau behavior is predicted for σ as a function of the Fermi energy ${\mathit{E}}_{\mathit{F}}$. If ${\mathit{E}}_{\mathit{F}}$ crosses a miniband σ increases, and if ${\mathit{E}}_{\mathit{F}}$ crosses a minigap σ stays constant. Under certain circumstances this causes an insulator-metal transition. The competition of this transition with the Mott transition is discussed, and the Mott criterion is adapted to SL’s. The general results are applied to GaAs and Si n-type δ-doping SL’s. From miniband structure calculations for various SL periods d and sheet-doping concentrations ${\mathit{N}}_{\mathit{D}}$ we derive conductivity plots σ(${\mathit{N}}_{\mathit{D}}$) and insulator-metal phase diagrams in the ${\mathit{N}}_{\mathit{D}}$-d plane.