Measurement of the valence-band offset in strained Si/Ge (100) heterojunctions by x-ray photoelectron spectroscopy

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Abstract
We have used x‐ray photoelectron spectroscopy to measure the valence‐band offset in situ for strained Si/Ge (100) heterojunctions grown by molecular beam epitaxy. Si 2p and Ge 3d core level to valence‐band‐edge binding energies and Si 2p to Ge 3d core level energy separations were measured as functions of strain, and strain configurations in all samples were determined using x‐ray diffraction. Our measurements yield valence‐band offset values of 0.83±0.11 eV and 0.22±0.13 eV for Ge on Si (100) and Si on Ge (100), respectively. If we assume that the offset between the weighted averages of the light hole, heavy hole, and spin‐orbit valence bands in Si and Ge is independent of strain, we obtain a discontinuity in the average valence‐band edge of 0.49±0.13 eV.