Exciton Binding Energy In Type-II GaAs-AlAs Quantum Well Heterostructures

Envelope function calculations indicate that the GaAs-AlAs band edge configuration changes from a straddled, type-I line-up to a staggered, type-II arrangement when the GaAs width is below about 32Å. The binding energy of the ground state exciton is calculated variationally for this heterojunction arrangement. Anisotropy in both electron and hole effective masses is considered and calculations performed assuming perfect confinement of both sorts of carriers. Calculated binding energies are of a similar magnitude to those of the is heavy hole exciton for this materials system when its band edge configuration is the more familiar type-I.