Geometric and electronic structure of a semiconductor superlattice

Esaki and Tsu 1 have proposed that a semiconductor superlattice (a periodically repeated arrangement of alternating layers of two III–V semiconductors) might exhibit negative differential mobility (NDM) if electrons could be injected into regions of negative effective mass in the band-structure created by the superlattice. A weak NDM has subsequently been observed 2 , but nothing more has been reported since then. We have recently seen strong NDM in a 21-period AlGaAs/GaAs superlattice 3 . The current–voltage ( I–V ) characteristics show fewer, but sharper, features than reported by Esaki and Chang 2 . Here we report the correlations between (1) the design and predicted performance of an ideal semiconductor superlattice and (2) the structure and actual performance of the 21-period superlattice. Calculations of the energy dependence of electron transmission through the ideal and the actual superlattice show gross band-structure features at similar energies. Fine structure in electron transmission through the actual superlattice may be the origin of fine structure in the measured I–V characteristics. The results imply a certain tolerance of the electronic structure towards modest fluctuations in the superlattice parameters, which may be of importance in the realization of superlattice devices.