title: Large electroabsorption susceptibility mediated by internal photoconductive gain in Ge nanowires.
abstract: Large spectral modulation in the photon-to-electron conversion near the absorption band-edge of a semiconductor by an applied electrical field can be a basis for efficient electro-optical modulators. This electro-absorption effect in Group IV semiconductors is, however, inherently weak, and this poses the technological challenges for their electro-photonic integration. Here we report unprecedentedly large electro-absorption susceptibility at the direct band-edge of intrinsic Ge nanowire (NW) photodetectors, which is strongly diameter-dependent. We provide evidence that the large spectral shift at the 1.55 μm wavelength, enhanced up to 20 times larger than Ge bulk crystals, is attributed to the internal Franz-Keldysh effect across the NW surface field of ~10(5) V/cm, mediated by the strong photoconductive gain. This classical size-effect operating at the nanometer scale is universal, regardless of the choice of materials, and thus suggests general implications for the monolithic integration of Group IV photonic circuits.
authors.affiliation: Department of Materials Science and Engineering, Yonsei University, Seongsan-No 262 Seodaemun-Gu, Seoul 120-749, Korea.
authors.forename: Hyun-Seung
authors.initials: HS
authors.lastname: Lee
authors.forename: Cheol-Joo
authors.initials: CJ
authors.lastname: Kim
authors.forename: Donghun
authors.initials: D
authors.lastname: Lee
authors.forename: Ru Ri
authors.initials: RR
authors.lastname: Lee
authors.forename: Kibum
authors.initials: K
authors.lastname: Kang
authors.forename: Inchan
authors.initials: I
authors.lastname: Hwang
authors.forename: Moon-Ho
authors.initials: MH
authors.lastname: Jo