Fermi-level pinning and Schottky barrier heights on epitaxially grown fully strained and partially relaxed n-type Si1-xGex layers

The Schottky barrier height on n-type Si1-xGex films has been studied as a function of the composition and strain relaxation. We have used electrical I-V measurements complemented by high-resolution x-ray measurements for assessment of the relaxation in the epilayers. In addition, Schottky barrier height on n-Si1-xGex films has also been investigated as a function of the metal work function. Our results shows that the barrier height on n-type Si1-xGex does not depend on either the Ge content or strain relaxation, but is sensitive to the metal work function. The experimental results indicate that the Fermi level is pinned to the conduction band and provide also the evidence that the pinning position of the Fermi level is metal work function dependent. This pinning behavior in metal Si1-xGex is opposed to that observed in metal/Si contacts, were the Fermi level is pinned either to the valence or conduction band depending on the metal work function. These findings regarding the relaxation independent barrier height on n-type Si1-xGex are suggesting only the movement of the valence band of Si1-xGex/Si heterostructure upon relaxation as expected. (C) 1999 American Institute of Physics. [S0021-8979(99)08524-2].