QUASI-BOUND STATES IN AN ASYMMETRIC GaAs-AlAs SUPERLATTICE

Abstract
Interband photoconductivity measurements have been performed on a "Quasi-Graded-Gap" Superlattice (QGGSL). A number of features, both sharp and broad, are observed in the photoresponse, corresponding to transitions between the quasi-bound states of the superlattice. These features are described by a calculation, within an envelope-function approximation, of the pseudo-stationary states of the QGGSL. It is found that the electrons chiefly tunnel through the barriers in the device via states associated with the X-conduction band minimum of AlAs. The calculation also shows that the emission lines seen in electroluminescence spectra are due to recombinations between electrons and light holes, as the light holes tunnel through the QGGSL much more readily.