title: Heterogeneously-Grown Tunable Tensile Strained Germanium on Silicon for Photonic Devices.
abstract: The growth, structural and optical properties, and energy band alignments of tensile-strained germanium (ε-Ge) epilayers heterogeneously integrated on silicon (Si) were demonstrated for the first time. The tunable ε-Ge thin films were achieved using a composite linearly graded InxGa1-xAs/GaAs buffer architecture grown via solid source molecular beam epitaxy. High-resolution X-ray diffraction and micro-Raman spectroscopic analysis confirmed a pseudomorphic ε-Ge epitaxy whereby the degree of strain varied as a function of the In(x)Ga(1-x)As buffer indium alloy composition. Sharp heterointerfaces between each ε-Ge epilayer and the respective In(x)Ga(1-x)As strain template were confirmed by detailed strain analysis using cross-sectional transmission electron microscopy. Low-temperature microphotoluminescence measurements confirmed both direct and indirect bandgap radiative recombination between the Γ and L valleys of Ge to the light-hole valence band, with L-lh bandgaps of 0.68 and 0.65 eV demonstrated for the 0.82 ± 0.06% and 1.11 ± 0.03% strained Ge on Si, respectively. Type-I band alignments and valence band offsets of 0.27 and 0.29 eV for the ε-Ge/In(0.11)Ga(0.89)As (0.82%) and ε-Ge/In(0.17)Ga(0.83)As (1.11%) heterointerfaces, respectively, show promise for ε-Ge carrier confinement in future nanoscale optoelectronic devices. Therefore, the successful heterogeneous integration of tunable tensile-strained Ge on Si paves the way for the design and implementation of novel Ge-based photonic devices on the Si technology platform.
authors.affiliation: Advanced Devices & Sustainable Energy Laboratory (ADSEL), Bradley Department of Electrical and Computer Engineering, Virginia Tech , Blacksburg, Virginia 24061, United States.
authors.forename: Michael
authors.initials: M
authors.lastname: Clavel
authors.affiliation: Tyndall National Institute , Lee Maltings, Dyke Parade, Cork, Ireland.|Centre for Advanced Photonics and Process Analysis, Cork Institute of Technology , Cork, Ireland.
authors.forename: Dzianis
authors.initials: D
authors.lastname: Saladukha
authors.affiliation: Advanced Devices & Sustainable Energy Laboratory (ADSEL), Bradley Department of Electrical and Computer Engineering, Virginia Tech , Blacksburg, Virginia 24061, United States.
authors.forename: Patrick S
authors.initials: PS
authors.lastname: Goley
authors.affiliation: Tyndall National Institute , Lee Maltings, Dyke Parade, Cork, Ireland.|Centre for Advanced Photonics and Process Analysis, Cork Institute of Technology , Cork, Ireland.
authors.forename: Tomasz J
authors.initials: TJ
authors.lastname: Ochalski
authors.affiliation: Tyndall National Institute , Lee Maltings, Dyke Parade, Cork, Ireland.
authors.forename: Felipe
authors.initials: F
authors.lastname: Murphy-Armando
authors.affiliation: Fluids Research Laboratory, Department of Geosciences, Virginia Tech , Blacksburg, Virginia 24061, United States.
authors.forename: Robert J
authors.initials: RJ
authors.lastname: Bodnar
authors.affiliation: Advanced Devices & Sustainable Energy Laboratory (ADSEL), Bradley Department of Electrical and Computer Engineering, Virginia Tech , Blacksburg, Virginia 24061, United States.
authors.forename: Mantu K
authors.initials: MK
authors.lastname: Hudait
keywords: efficient cost-effective light sources; germanium; heterostructure; laser integration; molecular beam epitaxy; optical domain