Electronic structure of epitaxial α-Sn 1-xGe x alloys

Abstract

The electronic structure and interface properties of α-Sn 1−xGe x alloy films grown by molecular beam epitaxy (MBE) on GaSb, CdTe and Ge(100) were studied by angle resolved synchrotron radiation photoemission spectroscopy (ARPES). Deposition at temperatures below ~150 C results In polycrystalline or amorphous films. At higher substrate temperatures GaSb and CdTe partially react with the overlayer forming either GeSb or SnTe in the Interface region. Homogeneous alloy films with good crystalline quality were grown on Ge(100) at ~400 C up to a critical thickness of 200–300Å. Photoemission core level analysis indicates a strong tendency to form an ordered compound with a composition close to x~0.5. Angle resolved valence band spectra show the shift of the Γ 8 point from ~0.6 eV in Ge(100) to ~0.16 eV below E F in the α-Sn 0.48 Ge 0.52 alloy. The experimental information of a constant alloy Fermi level locates the top of the Γ 8 valence band ~0.16 eV below E p. Assuming a linear band model, the direct band gap of Eg-0.2 eV for x~0.5 will then locate the bottom of the Γ 7 conduction band -0.04 eV above E F.