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Schematic of samples examined in this study. (a) Bulk samples, (b) bulk GeTe samples, (c) interface samples (GeTe on ), and (d) interface metal/GeTe samples (metal on GeTe).
XPS spectra obtained from the samples in this study. (a) bulk samples with core level and valence band, VB spectra. (b) 50 nm thick bulk samples with core level and valence band, VB spectra for as shown at the top (bottom) of the plot. (c) Interface samples 5 nm thick on with and core level spectra as shown at the top (bottom) of the plot. (d) Interface metal/GeTe samples 5 nm metal (Al, W, and Ni) on 50 nm thick with core level spectra as shown at the top (bottom) of the plot.
A schematic energy band diagram of the energy band offsets between and GeTe at both states. The top and bottom edges of each rectangle represent and , respectively. and can be inferred from the band diagram.
Experimentally extracted effective work functions of Al, W, and Ni on a-GeTe and c-GeTe were plotted using squares and triangle, respectively, against their respective vacuum work functions . The dashed line is given by , and represents the case where no pinning of metal Fermi-level occurs on the GeTe surface. The intercept (indicated by circle) of the dashed line and the linear fitted line represents the charge neutrality level of the GeTe at either state.
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