Electron-phonon coupling on strained Ge/Si(111)-(5×5) surfaces

Abstract

We investigate the structural and electronic properties of strained Ge/Si(111)-(5 × 5) surfaces by means of scanning tunneling microscopy and high-resolution angle-resolved photoemission spectroscopy. The homogeneous (5 × 5) reconstructed overlayers are characterized by three electronic surface states, similar to the Si( 111)-(7 × 7) surface. The dispersion of the dangling bond related surface state exhibits the same periodicity as that of the (5 × 5) reconstruction. Moreover, a careful analysis of the shape and width of this surface state provides striking evidence of electron-phonon coupling at low temperatures. By considering the spectral function within a simple Debye model, we determine both the Debye energy and the electron-phonon coupling strength. The latter value is further confirmed by analyzing the temperature-dependent phonon broadening of the dangling bond related surface state linewidth.

Giant electron-phonon interaction for a prototypical semiconductor interface: Sn/Ge(111)−(3×3)

“…We have found from experimental evidence that λ = 1.45 ± 0.1, a value much larger than the ones found for Si(111)-(7 × 7) [16], and Ge-Si(111)-(5 × 5) [17]; combining this result with our theoretical value, λ = 1.30, yields λ = 1.37 ± 0.10 which we consider to be a fair approximation to the value of λ for the α-Sn/Ge(111)-(3 × 3) surface.…”

“…tant e-ph interaction associated with partially occupied surface 48 bands has also been observed in Si(111)-(7 × 7) (λ = 1.06 49 [16]) and in Ge/Si-(5 × 5) (λ 0.53 [17]). Electron-phonon 50 coupling is thus an important element to accurately describe 51 semiconducting surfaces with metallic two-dimensional sur-52 face states, and to understand a possible superconductor state 53 and other phase transitions [2,15,18,19].…”

Epitaxial Ge Growth on Si(111) Covered with Ultrathin SiO<sub>2</sub> Films

“…After Ge island formation at the initial growth stage, the further Ge deposition or the sample annealing lead to the formation of large islands, when the temperature is in the range from 590˚C to 650˚C (Figure 4). The flat areas between the islands exhibit the 5 × 5 reconstruction which is normally observed for the 2 BL Ge wetting layers grown on the bare Si(111) substrates [29][30][31]. The (111) planes on top of the islands possess the 7 × 7 reconstruction that is similar for that known for Ge islands grown on the bare Si(111) surfaces [32][33][34].…”

“…The driving force for such surface morphology transformation is the lattice strain. The Ge growth on the bare Si(111) surfaces has been studied in details [6][7][8][9][10][11][12][13][14][15][16][17][18][29][30][31][32][33]. For comparison with the above results the STM data for the Ge growth on the bare Si(111) surfaces at temperatures of 530˚C are shown in Figure 5.…”

Band Gap Opening Induced by the Structural Periodicity in Epitaxial Graphene Buffer Layer

“…ε 1 is different from previously observed g1 and g2 states of the buffer layer as these states are visible in a larger region of the reciprocal space with a different symmetry (see Supporting Information (Figure S.1). ε 1 is compatible with the orientation of SiC Brillouin zones, with a size close to that of the (6 × 6) SiC , as seen in Figure b and c. High spectral weight is not expected in every Brillouin zone as the photoemission intensity is not necessarily periodic, − as particularly evident in the paradigmatic case of the (7 × 7) reconstruction of Si(111), where the spectral weight of the surface state does not seem to follow the (7 × 7) periodicity . This is due to the influence of the structure factor in photoemission, analogous to the situation in X-ray diffraction.…”