New insights into the electronic states of the Ge(001) surface by joint angle-resolved photoelectron spectroscopy and first-principle calculation investigation

• Published in: Applied surface science Vol. 571; p. 151264
• Main Authors: Reichmann, Felix, Scalise, Emilio, Becker, Andreas P., Hofmann, Emily V.S., Dabrowski, Jaroslaw, Montalenti, Francesco, Miglio, Leo, Mulazzi, Mattia, Klesse, Wolfgang M., Capellini, Giovanni
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 01.01.2022
• Subjects: ARPES; DFT; Germanium; Surface; Germanium; DFT; Ge; ARPES; Surface
• ISSN: 0169-4332; 1873-5584
• DOI: 10.1016/j.apsusc.2021.151264

[Display omitted] •ARPES on Ge(001) shows the occupation of the surface conduction band minimum at RT.•Temperature-dependent ARPES proves the occupation by thermally excited electrons.•First-principle calculations assign the states to the c(4 × 2) or p(2 × 2) reconstruction.•Combining experiment and theory the valence band structure is assigned to bulk states. While the Ge(001) surface has been extensively studied, it is still debated whether it is of conducting or semiconducting nature at room temperature. The evidence collected by angle-resolved photoelectron spectroscopy experiments in the past has led to the preliminary attribution of a semiconducting nature at room temperature. In contrast, we show in this work that the pristine Ge(001) surface is conducting at room temperature by using temperature-dependent angle-resolved photoelectron spectroscopy, scanning tunneling microscopy and first principles calculations. Specifically, a surface band located ∼200 meV above the valence band maximum has been observed at room temperature. This surface band shows anisotropic dispersions along the [010] and [110] directions, but it disappears at lower measurement temperature, which indicates its occupation by thermally excited electrons. State-of-the-art density functional theory calculations undoubtedly attribute this surface band to the unoccupied π*-band formed by dangling bonds on the c(4 × 2) surface reconstruction, while evidencing fundamental differences with the p(2 × 1) reconstruction. Furthermore, the calculations demonstrate that the valence band structure observed in angle-resolved photoelectron spectroscopy experiments arise from projected bulk states and is thus insensitive to surface contamination. Our results contribute to the fundamental knowledge of the Ge(001) surface and to a better understanding of its role in micro- and opto-electronic devices.