UNPINNED GAAS SCHOTTKY BARRIERS WITH AN EPITAXIAL SILICON LAYER

We present experimental results of Al/n- and Al/p-type GaAs Schottky barrier structures grown in situ by molecular-beam epitaxy with thin Si epitaxial interfacial layers. The barrier heights are measured by the I-V, thermal activation, C-V, and photoresponse methods. Barrier heights in the range of 0.3 < phi-bN < 1.04 eV for n-type GaAs and 0.28 < phi-bP < 1.01 eV for p-type GaAs were obtained for Si layer thicknesses between 6 and 100 angstrom. Annealing studies conducted on the samples indicate that the structures are thermally stable to temperatures up to 450-degrees-C. These results imply that the GaAs surface Fermi level at the Si/GaAs interface is unpinned from its customary near-midgap value. A model which involves the energy-band discontinuities DELTA-E(C) and DELTA-E(V) between GaAs and Si, the thickness, and the doping of the Si layer is suggested to account for the different barrier-height values obtained.