title: Direct-gap gain and optical absorption in germanium correlated to the density of photoexcited carriers, doping, and strain.
abstract: Direct-gap gain up to 850 cm(-1) at 0.74 eV is measured and modeled in optically pumped Ge-on-Si layers for photoexcited carrier densities of 2.0 × 10(20) cm(-3). The gain spectra are correlated to carrier density via plasma-frequency determinations from reflection spectra. Despite significant gain, optical amplification cannot take place, because the carriers also generate pump-induced absorption of ≈7000 cm(-1). Parallel studies of III-V direct-gap InGaAs layers validate our spectroscopy and modeling. Our self-consistent results contradict current explanations of lasing in Ge-on-Si cavities.
authors.affiliation: Laboratory for Micro- and Nanotechnology, Paul Scherrer Institut, Villigen, Switzerland.
authors.forename: Lee
authors.initials: L
authors.lastname: Carroll
authors.forename: Peter
authors.initials: P
authors.lastname: Friedli
authors.forename: Stefan
authors.initials: S
authors.lastname: Neuenschwander
authors.forename: Hans
authors.initials: H
authors.lastname: Sigg
authors.forename: Stefano
authors.initials: S
authors.lastname: Cecchi
authors.forename: Fabio
authors.initials: F
authors.lastname: Isa
authors.forename: Daniel
authors.initials: D
authors.lastname: Chrastina
authors.forename: Giovanni
authors.initials: G
authors.lastname: Isella
authors.forename: Yuriy
authors.initials: Y
authors.lastname: Fedoryshyn
authors.forename: Jérôme
authors.initials: J
authors.lastname: Faist