INTERFACIAL ATOMIC COMPOSITION AND SCHOTTKY-BARRIER HEIGHTS AT THE ALGAAS(001) INTERFACE/

The influence of different interfacial chemical compositions on the Sc hottky barrier heights across the Al/GaAs(001) interface is studied us ing first-principles local density functional calculations. The barrie r heights are calculated for seven different interfacial chemical comp ositions, including the chemically abrupt As-terminated and Ga-termina ted interfaces, and also several other interfaces related by Al <-- -- > Ga place exchange or containing As antisites. We find p-type barrier heights phi(p) that vary by 0.4 eV, demonstrating a significant influ ence of the interface composition on the resulting barrier heights. Th e barrier height variation is explained by the different chemical bond ing at the interface in the various cases. The metal induced gap state s (MIGS) of two structures with different barrier heights are compared in order to demonstrate why such states do not result in barrier heig hts independent of interfacial chemical composition. It is thus sugges ted that the reason an experimental value of phi(p) = 0.65 eV is gener ally found for Al/GaAs is not due to several possible interfacial stru ctures all having their Fermi level pinned by MIGS at the same value, but rather due to the thermodynamic preference for certain structures over others with significantly different barriers. This proposal offer s a potential explanation for recent photoemission experiments that fi nd the Fermi level position in the pp varying by several tenths of a v olt as a function of the initial surface structure of the GaAs substra te: some of the samples are likely to have interfacial compositions wh ich are metastable with respect to structures that give the standard b arrier heights.