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O'Mahony SM, Murphy-Armando F, Murray ÉD, Querales-Flores JD, Savić I, Fahy S. Ultrafast Relaxation of Symmetry-Breaking Photo-Induced Atomic Forces. Phys Rev Lett 2019; 123:087401. [PMID: 31491230 DOI: 10.1103/physrevlett.123.087401] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2019] [Revised: 05/24/2019] [Indexed: 06/10/2023]
Abstract
We present a first-principles method for the calculation of the temperature-dependent relaxation of symmetry-breaking atomic driving forces in photoexcited systems. We calculate the phonon-assisted decay of the photoexcited force on the low-symmetry E_{g} mode following absorption of an ultrafast pulse in Bi, Sb, and As. The force decay lifetimes for Bi and Sb are of the order of 10 fs and in agreement with recent experiments, demonstrating that electron-phonon scattering is the primary mechanism relaxing the symmetry-breaking forces. Calculations for a range of absorbed photon energies suggest that larger amplitude, symmetry-breaking atomic motion may be induced by choosing a pump photon energy which maximizes the product of the initial E_{g} force and its lifetime. The high-symmetry A_{1g} force undergoes a partial decay to a nonzero constant on similar timescales, which has not yet been measured in experiments. The average imaginary part of the electron self-energy over the photoexcited carrier distribution provides a crude indication of the decay rate of symmetry-breaking forces.
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Affiliation(s)
- Shane M O'Mahony
- Department of Physics, University College Cork, Cork T12K8AF, Ireland
- Tyndall National Institute, Cork T12R5CP, Ireland
| | | | - Éamonn D Murray
- Department of Physics and Department of Materials, Imperial College London, London SW7 2AZ, United Kingdom
| | | | - Ivana Savić
- Tyndall National Institute, Cork T12R5CP, Ireland
| | - Stephen Fahy
- Department of Physics, University College Cork, Cork T12K8AF, Ireland
- Tyndall National Institute, Cork T12R5CP, Ireland
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Clavel M, Saladukha D, Goley PS, Ochalski TJ, Murphy-Armando F, Bodnar RJ, Hudait MK. Heterogeneously-Grown Tunable Tensile Strained Germanium on Silicon for Photonic Devices. ACS Appl Mater Interfaces 2015; 7:26470-26481. [PMID: 26561963 DOI: 10.1021/acsami.5b07385] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/05/2023]
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.
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Affiliation(s)
- Michael Clavel
- Advanced Devices & Sustainable Energy Laboratory (ADSEL), Bradley Department of Electrical and Computer Engineering, Virginia Tech , Blacksburg, Virginia 24061, United States
| | - Dzianis Saladukha
- Tyndall National Institute , Lee Maltings, Dyke Parade, Cork, Ireland
- Centre for Advanced Photonics and Process Analysis, Cork Institute of Technology , Cork, Ireland
| | - Patrick S Goley
- Advanced Devices & Sustainable Energy Laboratory (ADSEL), Bradley Department of Electrical and Computer Engineering, Virginia Tech , Blacksburg, Virginia 24061, United States
| | - Tomasz J Ochalski
- Tyndall National Institute , Lee Maltings, Dyke Parade, Cork, Ireland
- Centre for Advanced Photonics and Process Analysis, Cork Institute of Technology , Cork, Ireland
| | | | - Robert J Bodnar
- Fluids Research Laboratory, Department of Geosciences, Virginia Tech , Blacksburg, Virginia 24061, United States
| | - Mantu K Hudait
- Advanced Devices & Sustainable Energy Laboratory (ADSEL), Bradley Department of Electrical and Computer Engineering, Virginia Tech , Blacksburg, Virginia 24061, United States
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Pavarelli N, Ochalski TJ, Murphy-Armando F, Huo Y, Schmidt M, Huyet G, Harris JS. Optical emission of a strained direct-band-gap Ge quantum well embedded inside InGaAs alloy layers. Phys Rev Lett 2013; 110:177404. [PMID: 23679775 DOI: 10.1103/physrevlett.110.177404] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Indexed: 06/02/2023]
Abstract
We studied the optical properties of a strain-induced direct-band-gap Ge quantum well embedded in InGaAs. We showed that the band offsets depend on the electronegativity of the layer in contact with Ge, leading to different types of optical transitions in the heterostructure. When group-V atoms compose the interfaces, only electrons are confined in Ge, whereas both carriers are confined when the interface consists of group-III atoms. The different carrier confinement results in different emission dynamics behavior. This study provides a solution to obtain efficient light emission from Ge.
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Affiliation(s)
- N Pavarelli
- Tyndall National Institute, University College Cork, Lee Maltings, Cork, Ireland
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Abstract
The role of reduced dimensionality and of the surface on electron-phonon (e-ph) coupling in silicon nanowires is determined from first principles. Surface termination and chemistry is found to have a relatively small influence, whereas reduced dimensionality fundamentally alters the behavior of deformation potentials. As a consequence, electron coupling to "breathing modes" emerges that cannot be described by conventional treatments of e-ph coupling. The consequences for physical properties such as scattering lengths and mobilities are significant: the mobilities for [110] grown wires are 6 times larger than those for [100] wires, an effect that cannot be predicted without the form we find for Si nanowire deformation potentials.
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Affiliation(s)
- F Murphy-Armando
- Tyndall National Institute, University College Cork, Lee Maltings, Cork, Ireland.
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Murphy-Armando F, Fahy S. First-principles calculation of alloy scattering in Ge(x)Si(1-x). Phys Rev Lett 2006; 97:096606. [PMID: 17026387 DOI: 10.1103/physrevlett.97.096606] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/02/2006] [Indexed: 05/12/2023]
Abstract
First-principles electronic structure methods are used to find the rates of intravalley and intervalley n-type carrier scattering due to alloy disorder in Si(1-x)Ge(x) alloys. The required alloy scattering matrix elements are calculated from the energy splitting of nearly degenerate Bloch states which arises when one average host atom is replaced by a Ge or Si atom in supercells containing up to 128 atoms. Scattering parameters for all relevant Delta and L intravalley and intervalley alloy scattering are calculated. Atomic relaxation is found to have a substantial effect on the scattering parameters. f-type intervalley scattering between Delta valleys is found to be comparable to other scattering channels. The n-type carrier mobility, calculated from the scattering rate using the Boltzmann transport equation in the relaxation time approximation, is in excellent agreement with experiments on bulk, unstrained alloys.
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Affiliation(s)
- F Murphy-Armando
- Tyndall National Institute, Lee Maltings, Prospect Row, Cork, Ireland
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