Correlation between barrier height and band offsets in metal/Si1-xGex/Si heterostructures

The variation of barrier height with the band gap in the metal/heterojunction systems is related to how the Fermi level position varies with respect to band edges. If the Fermi level is pinned by the interface states its movement will also correspond to the movement of the neutrality level at the interface. Metal/Si1-xGex/Si heterostructures (0 less than or equal to x less than or equal to 0.24) for both n- and p-type substrates were studied to understand the relation between Schottky barrier, Fermi level movement, and the band gap variations. It was shown that a correlation exists between Schottky barrier height variation and band- offset values Delta E-c and Delta E-v. For ntype substrate, measured barrier height differences are almost the same as the band offsets in the conduction band Delta E-c. For ptype substrates they were found to be slightly smaller than Delta E-v. This shows that Fermi level position relative to the conduction band edge does not change with band gap variation. (C) 1998 American Institute of Physics. [S0003-6951(98)05152-3]