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Evidence for strong Fermi-level pinning due to metal-induced gap states at metal/germanium interface
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Image of FIG. 1.
FIG. 1.

Experimentally obtained SBHs on and and reported metal work functions (see Refs. 7 and 8).

Image of FIG. 2.
FIG. 2.

(Color online) The SBH on for various metals. Regardless of the evaluation method, the Fermi level is strongly pinned near the valence band edge of Ge. The CNL is or from the Ge valence band edge, assuming and . The inset shows the examples of analysis.

Image of FIG. 3.
FIG. 3.

The SBH of and NiGe(엯) on . and phases were obtained by annealing at 200–400 and , respectively, while only NiGe phase was obtained by annealing . The work functions of and NiGe on are reported to be 4.05 and (see Ref. 17). A cross sectional TEM image of annealed interface is shown in the inset, where no interfacial layer is observed between NiGe and Ge.

Image of FIG. 4.
FIG. 4.

The SBH of Al(▵) and Au(▾) on Ge with three kinds of surface orientations. Only difference of SBH is observed among the (100), (110), and (111) oriented Ge surfaces, which suggests that interfacial characteristics hardly affect the CNL and the pinning strength at metal/Ge interfaces.


Generic image for table
Table I.

SBHs for estimated both by the method and partly by the method. Although the image force barrier lowering was taken into consideration, the maximum effect was of the order of , which was evaluated from potential energy variation in the depletion layer. Thus, the image force effect is not included in this table. The SBH value is an average of data points with error bars below for and for , respectively.

Generic image for table
Table II.

Experimentally obtained in this study and the theoretically calculated branch point in the literatures (Refs. 19 and 20). The CNL was measured from the valence band edge of Ge.


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752b84549af89a08dbdd7fdb8b9568b5 journal.articlezxybnytfddd
Scitation: Evidence for strong Fermi-level pinning due to metal-induced gap states at metal/germanium interface