Atomic and electronic structures of Si/Ge(100) interfaces studied by high-resolution photoelectron spectroscopy and scanning tunneling microscopy

Atomic-Scale Modification of Oxidation Phenomena on the Ge(100) Surface by Si Alloying

“…As shown earlier, the number of nonequivalent Si and Ge bonding sites at Si/Ge(100) interfaces strongly depends on the number of deposited silicon atoms. Therefore, we separately describe oxidation of interfaces with different nominal Si amounts, namely, 1 and 4 ML (hereafter Si 1ML /Ge and Si 4ML /Ge, respectively).…”

“…Therefore, we separately describe oxidation of interfaces with different nominal Si amounts, namely, 1 and 4 ML (hereafter Si 1ML /Ge and Si 4ML /Ge, respectively). The former structure can be considered as a model substrate for growing improved oxide films on Ge(100) since the Si atoms, which control the oxidation process in such junctions, have a single bonding site and form a well-defined crystalline buried Si 1– x Ge x alloy layer at Si 1ML /Ge . In the latter structure, the Si atoms have several bonding sites, illustrating the complexity of O–Si–Ge systems.…”

“…As the surface of Si 1ML /Ge is terminated by Ge atoms arranging the well-known (2×1) reconstruction (the corresponding LEED pattern is presented in the inset of Figure ), the Ge 3d spectrum should include individual components originating from different Ge atoms of this reconstruction, namely, the upper and lower atoms of buckled Ge dimers in the topmost layer as well as the second-layer Ge atoms. Indeed, our analysis indicates that the Ge 3d line shape in Figure a is composed of five spin–orbit components (depicted by filled doublets), among which Σ 1u , Σ 1d , and Σ′ 1 are very similar to the respective components for the clean Ge(100)(2 × 1) surface, that is, the components related to the dimer-up and dimer-down atoms of the topmost layer as well as Ge atoms in the second layer, respectively.…”

“…The substrate was kept at RT during Si deposition, followed by annealing the sample at 500 °C for 30 min. This leads to well-defined epitaxial Si/Ge structures with long-range order . Oxidation was performed at an O 2 pressure of 2 × 10 –7 Torr.…”

“…Furthermore, it is known that some drawbacks can arise as a result of Ge passivation with Si. For example, increasing the thickness of the Si layer can cause a decrease of carrier population in the higher-mobility Ge channel, and therefore, the Si layer thickness requires precise optimization. − Furthermore, physical realization of highly crystalline Si/Ge(100) interfaces is a nontrivial issue since the formation mechanism of strained Si/Ge(100) interfaces is governed by two opposite processes involving mass transport via the interface, namely, (i) Si indiffusion into the substrate and (ii) Ge segregation on top of the Si/Ge sample, leading to the formation of a buried Si 1‑ x Ge x alloy layer below the uppermost Ge (2 × 1)-reconstructed layer . Thus, the passivation of the Ge(100) substrate by Si atoms is actually not straightforward, and the oxidation mechanism for the Si-modified Ge(100) surface is not well understood yet.…”