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 function as is suggested by the Schottky-Mott theory. These metals were deposited in an ultra-high vacuum system on chemically etched (100) OMVPE-grown GaAs with a free carrier density of 10(16) cm(-3). It was, however, 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 group consists of Cu and the precious metals Ag, Au, Pd and Pt, which have a mean barrier height of 0.97 +/- 0.04 eV. This fact suggests that the Fermi level is pinned at energy levels in the band gap, of which the position (0.75, 0.61 and 0.45 eV above the valence band, respectively) 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 increases in the Schottky barrier height occurred at electronegativities of 1.30 (barrier height increased stepwise from 0.67 eV to 0.81 eV) and at 1.90 (from 0.81 eV to 0.97 eV). This relationship between Schottky barrier heights and Pauling's electronegativities of the contact metals suggests that interfacial chemistry plays a crucial role during Schottky barrier formation.