A newly developed first-principles quasiparticle theory is used to calculate the band offset at the (001) interface and band gaps in 1×1 and 2×2 superlattices of GaAs-AlAs heterojunctions. We find a sizable many-body contribution to the valence-band offset which is dominated by the many-body corrections to bulk GaAs and AlAs quasiparticle energies. The resultant offset Δ${\mathit{E}}_{\mathit{v}}$=0.53±0.05 eV is in good agreement with the recent experimental values of 0.50–0.56 eV. Our calculated direct band gaps for ultrathin superlattices are also in good agreement with experiment. The ${\mathit{X}}_{1\mathit{c}}$-derived state at point Γ¯, is however, above the ${\mathrm{\Gamma }}_{1\mathit{c}}$-derived state for both the 1×1 and 2×2 lattices, contrary to results obtained under the virtual-crystal approximation (a limiting case for the Kronig-Penny model) and some previous local-density-approximation (corrected) calculations. The differences are explained in terms of atomic-scale localizations and many-body effects. Oscillator strengths and the effects of disorder on the spectra are discussed.

• Received 27 December 1989

DOI:https://doi.org/10.1103/PhysRevB.41.10058