Origin of Fermi-level pinning and its control on the n-type Ge(100) surface

: Kuzmin M, Laukkanen P, Makela J, Tuominen M, Yasir M, Dahl J, Punkkinen MPJ, Kokko K

Publisher: AMER PHYSICAL SOC

: 2016

: Physical Review B

: PHYSICAL REVIEW B

: PHYS REV B

: ARTN 035421

: 94

: 3

: 8

: 2469-9950

DOI: https://doi.org/10.1103/PhysRevB.94.035421

Strong Fermi-level pinning (FLP) near the valence-band maximum on n-type Ge surfaces has been a longstanding challenge in semiconductor physics, and the nature of this phenomenon has been heavily debated for years. Here, we report a systematic synchrotron-based photoemission study of atomically well-defined Ge(100) surfaces and interfaces to elucidate the origin of FLP in such systems. It is experimentally shown that the FLP on n-Ge is not due to the dangling-bond, back-bond, and defect states, but is strongly contributed by the evanescent state of the Ge bulk. The conditions required for alleviating the FLP and even the implementation of a flatband structure on Ge(100) are formulated. Such a structure is realized in the BaO/Ge(100) system where one can obtain control over the Fermi-level position in the Ge gap. These findings are not only important from a fundamental viewpoint, but also open a route to producing Ohmic metal-insulator-semiconductor contacts for n-type Ge-based technology.