Band structure and confined energy levels of the Si₃N₄/Si/GaAs system

The band structure of strained Si (4-10 ML) on (001) GaAs, band lineups of the strained Si/(001)GaAs heterojunction, and confined energy levels of the Si₃N⁴/Si/GaAs quantum well have been calculated via a pseudopotential method. It has been found that in this technically important Si₃N₄/Si/(001)GaAs structure, strained Si has a very narrow band gap (0.34 eV) at the Δ_⊥ point in the Brillouin zone. For the strained Si/(001)GaAs heterojunction, the conduction band offsets from the Δ_⊥ for Si to the Γ valley for GaAs is 0.83 eV, and that from the Δ_⊥ valley for Si to the X valley for GaAs is 1.21 eV. The valence band offset is 0.25 eV. The lowest confined energy level in the conduction band of the Si₃N₄/Si/GaAs quantum well ranging from 4 to 10 monolayers is found to be 0.22-0.28 eV above the conduction band edge of strained Si, or 0.57-0.61 eV below the conduction band edge of GaAs, while the first confined energy level in the valence band is barely above the valence band maximum of GaAs. The accumulation and inversion take place at these confined energy levels.