METAL OVERLAYERS ON THE MBE-GROWN ZNSE(001) SURFACE

N-type ZnSe thin films have been grown by MBE on GaAs (001) surfaces a nd capped with an amorphous selenium layer. The Se cap was thermally d esorbed under ultrahigh vacuum to recover the (2 x 1) and c(2 x 2) rec onstructed surfaces, Selected metal contact formation was monitored us ing core and valence level photoelectron emission spectroscopy by in-s itu exposure of the surface to heated sources of Au, Ag and Pb. In eac h case, lineshape analysis of emission spectra indicated a low level o f interfacial mixing and provided an insight into the metal layer grow th mode, Both Au and Ag were found to grow in closely spaced islands o f approximately equal height. The morphology of Au and Ag layers was c onfirmed by cross-sectional transmission electron microscopy. Monitori ng of core and valence level emission peak positions allowed the deter mination of the metal-n-ZnSe Schottky barrier height, for a sufficient ly thick metallic layer. Measurements on this wide-gap semiconductor, even at 300 K, were influenced by the presence of a surface photovolta ge, which could be identified and subtracted for a fully-formed metall ic layer. The n-type ZnSe Schottky barrier heights inferred from the r elative Fermi level shifts (Phi(BN)(Au) = 1.74 eV, Phi(BN)(Ag) = 1.47 eV and Phi(BN)(Pb) = 1.25 eV), were found to scale with the metal work function for these three unreactive interfaces.