Consider a heterojunction between two semiconductormaterials, A and B, whose electron affinities are equal. Their energy band gaps are EgA= 1.0 eV and EgB= 2.0 eV. The cubic lattice constant may be assumed to be a = 6.00Å for each material, and the dielectric constant to be 10ε0 throughout the heterojunction. In all cases you may assume flat-band conditions within each material. (a) Draw the energy band edge diagram and compute ΔEC and ΔEV for this heterojunction, assuming that the electron affinity rule is valid. (b) Now suppose that both materials have a “midgap” energy at the exact midpoint of their energy band gaps, and that in each material a deviation of the Fermi level from the “midgap” energy at a heterojunction interface produces a charge density at the interface of –σ(EF-Emidgap) with σ = 1×1014q/cm2·eV. Assume that these charges in each material are separated from each other by one cubic lattice constant at the heterojunction interface. By requiring overall charge neutrality in the heterojunction and consistency of the heterojunction dipole with the band offset, compute the numerical values of the conduction-band and valence-band offsets and draw the resulting banddiagram. You should assume that in the absence of any interface dipole, the electron affinity rule is valid. While this model is overly simplistic, it captures some of the effects of so-called midgap alignment energies. (For the concept of midgap energies, you may see Phys Rev B 38 6305 (1988)and
Consider a heterojunction between two semiconductormaterials, A and B, whose electron affinities are equal. Their energy band gaps are EgA= 1.0 eV and EgB= 2.0 eV. The cubic lattice constant may be assumed to be a = 6.00Å for each material, and the dielectric constant to be 10ε0 throughout the heterojunction. In all cases you may assume flat-band conditions within each material.
(a) Draw the energy band edge diagram and compute ΔEC and ΔEV for this heterojunction, assuming that the
(b) Now suppose that both materials have a “midgap” energy at the exact midpoint of their energy band gaps, and that in each material a deviation of the Fermi level from the “midgap” energy at a heterojunction interface produces a charge density at the interface of –σ(EF-Emidgap) with σ = 1×1014q/cm2·eV. Assume that these charges in each material are separated from each other by one cubic lattice constant at the heterojunction interface. By requiring overall charge neutrality in the heterojunction and consistency of the heterojunction dipole with the band offset, compute the numerical values of the
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