title: Optical Properties of Nanoporous Germanium Thin Films.
abstract: In the present article we report enhanced light absorption, tunable size-dependent blue shift, and efficient electron-hole pairs generation in Ge nanoporous films (np-Ge) grown on Si. The Ge films are grown by sputtering and molecular beam epitaxy; subsequently, the nanoporous structure is obtained by Ge+ self-implantation. We show, by surface photovoltage spectroscopy measurements, blue shift of the optical energy gap and strong signal enhancement effects in the np-Ge films. The blue shift is related to quantum confinement effects at the wall separating the pore in the structure, the signal enhancement to multiple light-scattering events, which result in enhanced absorption. All these characteristics are highly stable with time. These findings demonstrate that nanoporous Ge films can be very promising for photovoltaic applications.
authors.affiliation: †Dipartimento di Fisica e Astronomia, Università di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Cavalcoli
authors.affiliation: ‡CNR-IMM MATIS and Dipartimento di Fisica e Astronomia, Università di Catania,Via S. Sofia 64, 95123 Catania, Italy.
authors.forename: Giuliana
authors.initials: G
authors.lastname: Impellizzeri
authors.affiliation: ‡CNR-IMM MATIS and Dipartimento di Fisica e Astronomia, Università di Catania,Via S. Sofia 64, 95123 Catania, Italy.
authors.forename: Lucia
authors.initials: L
authors.lastname: Romano
authors.affiliation: ‡CNR-IMM MATIS and Dipartimento di Fisica e Astronomia, Università di Catania,Via S. Sofia 64, 95123 Catania, Italy.
authors.forename: Maria
authors.initials: M
authors.lastname: Miritello
authors.affiliation: ‡CNR-IMM MATIS and Dipartimento di Fisica e Astronomia, Università di Catania,Via S. Sofia 64, 95123 Catania, Italy.
authors.forename: Maria Grazia
authors.initials: MG
authors.lastname: Grimaldi
authors.affiliation: †Dipartimento di Fisica e Astronomia, Università di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy.
authors.forename: Beatrice
authors.initials: B
authors.lastname: Fraboni
keywords: ion implantation; light trapping; nanoporous germanium; photovoltaic applications; quantum confinement; surface photovoltage