| 1. |
- Korlacki, R., et al.
(författare)
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Linear strain and stress potential parameters for the three fundamental band to band transitions in beta-Ga2O3
- 2022
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Ingår i: Applied Physics Letters. - : AIP Publishing. - 0003-6951 .- 1077-3118. ; 120:4
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Tidskriftsartikel (refereegranskat)abstract
- We report the strain and stress relationships for the three lowest energy direct band to band transitions at the Brillouin zone center in monoclinic beta-Ga2O3. These relationships augment four linear perturbation parameters for situations, which maintain the monoclinic symmetry, which are reported here as numerical values obtained from density functional theory calculations. With knowledge of these perturbation parameters, the shift of each of the three lowest band to band transition energies can be predicted from the knowledge of the specific state of strain or stress, thus providing a useful tool for modeling performance of power electronic devices and rational strain engineering in heteroepitaxy.
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| 2. |
- Korlacki, R., et al.
(författare)
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Strain and stress relationships for optical phonon modes in monoclinic crystals with beta-Ga2O3 as an example
- 2020
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 102:18
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Tidskriftsartikel (refereegranskat)abstract
- Strain-stress relationships for physical properties are of interest for heteroepitaxial material systems, where strain and stress are inherent due to thermal expansion and lattice mismatch. We report linear perturbation theory strain and stress relationships for optical phonon modes in monoclinic crystals for strain and stress situations which maintain the monoclinic symmetry of the crystal. By using symmetry group analysis and phonon frequencies obtained under various deformation scenarios from density-functional perturbation theory calculations on beta-Ga2O3, we obtain four strain and four stress potential parameters for each phonon mode. We demonstrate that these parameters are sufficient to describe the frequency shift of the modes regardless of the stress or strain pattern which maintain the monoclinic symmetry of the crystal. The deformation potentials can be used together with experimentally determined phonon frequency parameters from Raman or infrared spectroscopy to evaluate the state of strain or stress of beta-Ga2O3, for example, in epitaxial heterostructures.
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| 3. |
- Mock, Alyssa, et al.
(författare)
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Lattice dynamics of orthorhombic NdGaO3
- 2019
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Ingår i: Physical Review B. - : AMER PHYSICAL SOC. - 2469-9950 .- 2469-9969. ; 99:18
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Tidskriftsartikel (refereegranskat)abstract
- A complete set of infrared-active and Raman-active lattice modes is obtained from density functional theory calculations for single-crystalline centrosymmetric orthorhombic neodymium gallate. The results for infrared-active modes are compared with an analysis of the anisotropic long-wavelength properties using generalized spectroscopic ellipsometry. The frequency-dependent dielectric function tensor and dielectric loss function tensor of orthorhombic neodymium gallium oxide are reported in the spectral range of 80-1200 cm(-1). A combined eigendielectric displacement vector summation and dielectric displacement loss vector summation approach augmented by considerations of lattice anharmonicity is utilized to describe the experimentally determined tensor elements. All infrared-active transverse and longitudinal optical mode pairs obtained from density functional theory calculations are identified by our generalized spectroscopic ellipsometry investigation. The results for Raman-active modes are compared to previously published experimental observations. Static and high-frequency dielectric constants from theory as well as experiment are presented and discussed in comparison with values reported previously in the literature.
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| 4. |
- Stokey, M., et al.
(författare)
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Infrared active phonons in monoclinic lutetium oxyorthosilicate
- 2020
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Ingår i: Journal of Applied Physics. - : AMER INST PHYSICS. - 0021-8979 .- 1089-7550. ; 127:11
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Tidskriftsartikel (refereegranskat)abstract
- A combined generalized spectroscopic ellipsometry measurement and density functional theory calculation analysis is performed to obtain the complete set of infrared active phonon modes in Lu2SiO5 with a monoclinic crystal structure. Two different crystals, each cut perpendicular to a different crystal axis, are investigated. Ellipsometry measurements from 40 to 1200 cm(-1) are used to determine the frequency dependent dielectric function tensor elements. The eigendielectric displacement vector summation approach and the eigendielectric displacement loss vector summation approach, both augmented with anharmonic lattice broadening parameters proposed recently for low-symmetry crystal structures [Mock et al., Phys. Rev. B 95, 165202 (2017)], are applied for our ellipsometry data analysis. All measured and model calculated dielectric function tensor and inverse dielectric function tensor elements match excellently. 23 A(u) symmetry and 22 B-u symmetry infrared active transverse and longitudinal optical modes are found. We also determine the directional limiting modes and the order of the phonon modes within the monoclinic plane. Results from density functional theory and ellipsometry measurements are compared and nearly perfect agreement is observed. We further compare our results to those obtained recently for the monoclinic crystal Y2SiO5, which is isostructural to Lu2SiO5 [Mock et al., Phys. Rev. B 97, 165203 (2018)]. We find that the lattice mode behavior of monoclinic Lu2SiO5 is qualitatively identical with Y2SiO5 and differs only quantitatively. We anticipate that members of the isostructural group of monoclinic symmetry oxyorthosilicates such as Dy2SiO5 or Yb2SiO5 will likely behave very similar in their phonon mode properties as reported here for Lu2SiO5. Published under license by AIP Publishing.
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