Angle-resolved photoemission study of thin molecular-beam-epitaxy-grown α-${\mathrm{Sn}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Ge}}_{\mathrm{x}}$ films with x∼0.5

Angle-resolved synchrotron-radiation photoemission spectroscopy is used to study the electronic structure of metastable epitaxial films of α-${\mathrm{Sn}}_{1\mathrm{-}\mathrm{x}}$${\mathrm{Ge}}_{\mathrm{x}}$ alloys. Homogeneous crystalline alloy films were grown by molecular-beam epitaxy on Ge(100) substrates at ∼400 °C up to a thickness of ∼300 Å. Photoemission core-level analysis indicates a strong tendency to form a compound with a composition close to x∼0.5. Angle-resolved spectra show a shift of the ${\Gamma }_8$ valence band from ∼0.6 eV in Ge(100) to ∼0.16 eV below $E_F$ in the α-${\mathrm{Sn}}_{0.48}$${\mathrm{Ge}}_{0.52}$ alloy. The experimental information of a constant alloy Fermi level locates the top of the ${\Gamma }_8$ valence band ∼0.16 eV below $E_F$. Assuming a linear band model, the direct band gap of $E_g$∼0.2 eV for x∼0.5 will then locate the bottom of the ${\Gamma }_7$ conduction band ∼0.04 eV above $E_F$.