Temperature evolution of the band gap in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mi>BiFeO</mml:mi><mml:mn>3</mml:mn></mml:msub></mml:math>traced by resonant Raman scattering

Weber, Mads C.; Guennou, Maël; Toulouse, Constance; Cazayous, M.; Gillet, Yannick; Gonze, Xavier; Kreisel, J.

doi:10.1103/physrevb.93.125204

Cited by 21 publications

(14 citation statements)

References 44 publications

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“…While anomalies might arise from fitting the featureless absorption edge of Fig. 2(a), atypical band-gap temperature-dependence has been previously explained as due to lattice expansion [55] or (in perovskites) to distinctly evolving direct and indirect gaps [76]. In AgGaSe 2 a similarly small 30 meV redshift of an unambiguous direct gap and anomalous temperature evolution was found between 15 and 300 K and explained as arising from negative thermal expansion (also predicted here for Cu 3 N) [77].…”

Section: Discussionmentioning

confidence: 91%

Atypically small temperature-dependence of the direct band gap in the metastable semiconductor copper nitrideCu3N

et al. 2017

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The temperature-dependence of the direct band gap and thermal expansion in the metastable anti-ReO 3 semiconductor Cu 3 N are investigated between 4.2 and 300 K by Fourier-transform infrared spectroscopy and x-ray diffraction. Complementary refractive index spectra are determined by spectroscopic ellipsometry at 300 K. A direct gap of 1.68 eV is associated with the absorption onset at 300 K, which strengthens continuously and reaches a magnitude of 3.5×10 5 cm −1 at 2.7 eV, suggesting potential for photovoltaic applications. Notably, the direct gap redshifts by just 24 meV between 4.2 and 300 K, giving an atypically small band-gap temperature coefficient dE g /dT of −0.082 meV/K. Additionally, the band structure, dielectric function, phonon dispersion, linear expansion, and heat capacity are calculated using density functional theory; remarkable similarities between the experimental and calculated refractive index spectra support the accuracy of these calculations, which indicate beneficially low hole effective masses and potential negative thermal expansion below 50 K. To assess the lattice expansion contribution to the band-gap temperature-dependence, a quasiharmonic model fit to the observed lattice contraction finds a monotonically decreasing linear expansion (descending past 10 −6 K −1 below 80 K), while estimating the Debye temperature, lattice heat capacity, and Grüneisen parameter. Accounting for lattice and electron-phonon contributions to the observed band-gap evolution suggests average phonon energies that are qualitatively consistent with predicted maxima in the phonon density of states. As band-edge temperature-dependence has significant consequences for device performance, copper nitride should be well suited for applications that require a largely temperature-invariant band gap.

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Section: Discussionmentioning

confidence: 91%

Atypically small temperature-dependence of the direct band gap in the metastable semiconductor copper nitrideCu3N

et al. 2017

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“…Figure 1 shows characteristic Raman spectra measured on the two different domain regions, which are marked by asterisks in the inset, with the analyser being parallel to the polarisation of the incident light (VV). The spectra were excited with a laser line of 633 nm, which ensures non-resonant conditions and a relatively high integrated intensity of the first order Raman signal at room temperature 35 . On one hand the 633 nm excitation allows the use of the Raman tensor formalism for the assignment of Raman modes.…”

Section: Resultsmentioning

confidence: 99%

Ferroelastic domain identification in BiFeO3 crystals using Raman spectroscopy

Himcinschi

Rix

Röder

et al. 2019

Sci Rep

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Multiferroic BiFeO3 crystals were investigated by means of micro-Raman spectroscopy using the laser wavelengths of 442 nm (resonant conditions) and 633 nm (non-resonant conditions). The azimuthal angle dependence of the intensity of the Raman modes allowed their symmetry assignment. The experimental data are consistent with a simulation based on Raman tensor formalism. Mixed symmetries were taken into account, considering the orientation of the crystal optic axis along a pseudo-cubic <111> direction. The strong anisotropic intensity variation of some of the polar Raman modes was used for line scans and mappings in order to identify ferroelastic domain patterns. The line scans performed with different excitation wavelengths and hence different information depths indicate a tilt of the domain walls with respect to the sample surface. The domain distribution found by Raman spectroscopy is in very good agreement with the finding of electron back scattering diffraction.

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“…Resonant first-order and second-order Raman scattering processes may have e.g. different temperature behavior 19 , whose most natural interpretation invoke characteristics of the direct and indirect gaps. For classical semiconductors such as silicon (and Ge, III-V etc), the analysis of second-order Raman spectra was facilitated by the use of simple Hamiltonians, based on the effective mass approximation or on semi-empirical pseudopotentials, with model phonon band structure, model electron-phonon interaction and, in some cases, the inclusion of Wannier-Mott excitons [20][21][22][23][24] .…”

Section: Introductionmentioning

confidence: 99%

Ab Initio Approach to Second-order Resonant Raman Scattering Including Exciton-Phonon Interaction

Gillet

Kontur

Giantomassi

et al. 2017

Sci Rep

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Raman spectra obtained by the inelastic scattering of light by crystalline solids contain contributions from first-order vibrational processes (e.g. the emission or absorption of one phonon, a quantum of vibration) as well as higher-order processes with at least two phonons being involved. At second order, coupling with the entire phonon spectrum induces a response that may strongly depend on the excitation energy, and reflects complex processes more difficult to interpret. In particular, excitons (i.e. bound electron-hole pairs) may enhance the absorption and emission of light, and couple strongly with phonons in resonance conditions. We design and implement a first-principles methodology to compute second-order Raman scattering, incorporating dielectric responses and phonon eigenstates obtained from density-functional theory and many-body theory. We demonstrate our approach for the case of silicon, relating frequency-dependent relative Raman intensities, that are in excellent agreement with experiment, to different vibrations and regions of the Brillouin zone. We show that exciton-phonon coupling, computed from first principles, indeed strongly affects the spectrum in resonance conditions. The ability to analyze second-order Raman spectra thus provides direct insight into this interaction.

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Temperature evolution of the band gap inBiFeO3traced by resonant Raman scattering

Cited by 21 publications

References 44 publications

Atypically small temperature-dependence of the direct band gap in the metastable semiconductor copper nitrideCu3N

Atypically small temperature-dependence of the direct band gap in the metastable semiconductor copper nitrideCu3N

Ferroelastic domain identification in BiFeO3 crystals using Raman spectroscopy

Ab Initio Approach to Second-order Resonant Raman Scattering Including Exciton-Phonon Interaction

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