Cathodoluminescence spectroscopy of metal–semiconductor interface structures

Abstract

Low-energy cathodoluminescence spectroscopy (CLS) is a powerful new technique for characterizing the electronic structure of semiconductor surfaces and ‘‘buried’’ metal–semiconductor interfaces. This extension of a more conventional electron microscopy technique provides information on localized states, deep-level defects, and band structure of new compounds at interfaces below the free solid surface. Specifically, CLS provides direct identification of metal-induced interface states which evolve in energy and density with multilayer metal coverages of the particular metal, extrinsic surface states due to lattice disruption, as well as bulk defect levels—all of which can play a role in Schottky barrier formation. From the energy dependence of spectral features, one can distinguish interface versus bulk state emission and assess the relative spatial distribution of states below the free surface. From the dependence of spectral intensity on injection level, one can spatially resolve large differences in recombination dynamics and band bending across semiconductor surfaces, depending on their detailed morphology. Unlike surface-science techniques sensitive to only the outer few monolayers, low-energy CLS reveals the electronic structure of buried interfaces and their changes with thermal processing at overlayer thicknesses which permit bulk chemical interactions to occur. For metal–semiconductor interfaces, these CLS spectral features provide a new perspective on physical mechanisms of Schottky barrier formation.