Correlation between barrier height and band offsets in metal/Si_1-xGe_x/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/Si_1-xGe_x/Si heterostructures (0≤x≤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 ΔE_c and ΔE_v. For n-type substrate, measured barrier height differences are almost the same as the band offsets in the conduction band ΔE_c. For p-type substrates they were found to be slightly smaller than ΔE_v. This shows that Fermi level position relative to the conduction band edge does not change with band gap variation.