FERMI-LEVEL PINNING BY VARIOUS METAL SCHOTTKY CONTACTS ON (100)-OMVPE-GROWN N-GAAS

Of 17 metals that were investigated, it was found that there exists no linear relationship between Schottky barrier height and metal work fu nction as is suggested by the Schottky-Mott theory. These metals were deposited in an ultra-high vacuum system on chemically etched (100) OM VPE-grown GaAs with a free carrier density of 10(16) cm(-3). It was, h owever, possible to distinguish between three ''groups'' of metals on the basis of Schottky barrier height. The first group consists only of Y and Mg (mean barrier height of 0.67 +/- 0.07 eV) and the second of Al, Hf, Mn, V, Ti, Cr, Fe, Co and Ni (0.81 +/- 0.04 eV). The third gro up consists of Cu and the precious metals Ag, Au, Pd and Pt, which hav e a mean barrier height of 0.97 +/- 0.04 eV. This fact suggests that t he Fermi level is pinned at energy levels in the band gap, of which th e position (0.75, 0.61 and 0.45 eV above the valence band, respectivel y) depends on which of these three ''groups'' a metal belongs to. The first, second and third groups covered electronegativity ranges from 1 .22 to 1.31, 1.30 to 1.91 and 1.90 to 2.54, respectively. Stepwise inc reases in the Schottky barrier height occurred at electronegativities of 1.30 (barrier height increased stepwise from 0.67 eV to 0.81 eV) an d at 1.90 (from 0.81 eV to 0.97 eV). This relationship between Schottk y barrier heights and Pauling's electronegativities of the contact met als suggests that interfacial chemistry plays a crucial role during Sc hottky barrier formation.