Weak phonon modes observation using infrared reflectivity for 4H, 6H and 15R polytypes

Bluet, Jean‐Marie; Chourou, K; Anikin, M. M.; Madar, R.

doi:10.1016/s0921-5107(98)00504-2

Cited by 19 publications

(23 citation statements)

References 7 publications

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“…The axial modes consist of Raman active A 1 and Raman inactive B 1 modes. Our vibrational frequencies at Γ point are in excellent agreement with previously published calculations and with experimental phonon dispersion curves obtained by infrared and Raman spectroscopies [68][69][70][71][72], being the average error smaller than 4 cm −1 . This supports our choice of using DFT-LDA eigenergies and DFPT-LDA phonon frequencies as key ingredients for the calculation of the electron-phonon interaction.…”

Section: Phonons Of Hexagonal Silicon Carbidessupporting

confidence: 91%

Thermal evolution of silicon carbide electronic bands

Cannuccia

Gali²

2020

Phys. Rev. Materials

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Direct observation of temperature dependence of individual bands of semiconductors for a wide temperature region is not straightforward, in particular, for bands farther from the Fermi-level. However, this fundamental property is a prerequisite in understanding the electron-phonon coupling of semiconductors. Here we apply ab initio many body perturbation theory to the electron-phonon coupling on hexagonal silicon carbide (SiC) crystals and determine the temperature dependence of the bands. We find a significant electron-phonon renormalization of the band gap at 0 K. Both the conduction and valence bands shift at elevated temperatures exhibiting a different behavior. We compare our theoretical results with the observed thermal evolution of SiC band edges, and discuss our findings in the light of high temperature SiC electronics and defect qubits operation.Electron-phonon interaction impacts a large variety of fundamental materials properties [1], from the critical temperature of superconductors to the zero-point renormalization and the temperature dependence of the electronic energy bands, from the electronic band gaps [2][3][4][5][6] to the thermal evolution of the optical spectra and excitonic lifetimes [7][8][9]. In addition the electron-phonon coupling contributes to the optical absorption and emission in indirect gap semiconductors [10][11][12], determines the electronic carrier mobility of semiconductors [13], the carrier relaxation rates [14], the distortion of band structures and phonon dispersion giving rise to kinks and Kohn anomalies in photoemission [15].Direct observation of the temperature evolution of individual bands over a wide region of temperatures is not straightforward. Optical techniques are capable of measuring band gaps, and not the absolute values of the valence band maximum (VBM) and the conduction band minimum (CBM) separately. The interpretation of results from optical techniques is then weakly conclusive. In addition, the indirect band gap nature of some materials prohibits the direct optical transition between VBM and CBM, which turns to be allowed only when phonons assist the optical excitation. Recent attempts used Si 2p core level as a reference to extract the CBM and VBM energy position of Si and hexagonal 6H silicon carbide (SiC) crystals [see Fig. 1(a)] from the onset of soft X-ray absorption spectroscopy (XAS) and soft non-resonant Xray emission spectroscopy (XES), respectively [16,17]. This method assumes temperature independent core exciton binding energy [18], which results in a systematically smaller derived band gap than the observed optical band gap, and it may suffer from the accurate observation of the onset energies at elevated temperatures caused by temperature broadening effects. We stress that none of these methods enables the observation of individual bands other than band edges but observation of the tem-perature dependence of those bands can be an important issue at high temperatures.It is utterly important to apply ab initio many body perturbation theory that ca...

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Section: Phonons Of Hexagonal Silicon Carbidessupporting

confidence: 91%

Thermal evolution of silicon carbide electronic bands

Cannuccia

Gali²

2020

Phys. Rev. Materials

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“…1Schematic of the ZLFO-SPhP hybridisation scheme. a Illustration of LO phonon dispersion parallel to the c -axis in 2H- and 4H-SiC 29 . The wavevector is normalised over the 2H-SiC Brillouin zone border k M = π / a where a is the length of the 2H-SiC unit cell along the c -axis.…”

Section: Introductionmentioning

confidence: 99%

“…The ZFLO modes we exploit, typically termed weak phonons, are high-wavevector states accessible near the Γ point due to Bragg scattering induced by the periodicity of the crystal lattice. They manifest as a dip in planar reflectance and are usually phenomenologically described by adding oscillators to the material's transverse dielectric function 28,29 . The negative dispersion of the LO phonon ensures that these weak phonon modes exist within the Reststrahlen band, co-existing in frequency with propagating or localised SPhPs 17 .…”

Section: Introductionmentioning

confidence: 99%

Hybrid longitudinal-transverse phonon polaritons

et al. 2019

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Phonon polaritons, hybrid light-matter quasiparticles resulting from strong coupling of the electromagnetic field with the lattice vibrations of polar crystals are a promising platform for mid-infrared photonics but for the moment there has been no proposal allowing for their electrical pumping. Electrical currents in fact mainly generate longitudinal optical phonons, while only transverse ones participate in the creation of phonon polaritons. We demonstrate how to exploit long-cell polytypes of silicon carbide to achieve strong coupling between transverse phonon polaritons and zone-folded longitudinal optical phonons. We develop a microscopic theory predicting the existence of the resulting hybrid longitudinal-transverse excitations. We then provide an experimental observation by tuning the resonance of a nanopillar array through the folded longitudinal optical mode, obtaining a clear spectral anti-crossing. The hybridisation of phonon polaritons with longitudinal phonons could represent an important step toward the development of phonon polariton-based electrically pumped mid-infrared emitters.

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“…Variations in the fringe oscillation frequencies suggest a graded strain distribution, and the broad shoulder is consistent with a thin damaged subsurface layer. 10,11 The SiC:Ge with Ge= 0.07% had a broad band at 948 cm −1 that decreased to 943 cm −1 for Ge= 1.25%. Figure 2 shows the reflectance in the reststrahlen band, revealing the axial folded-transverse-optic (FTO) mode of 4H-SiC at 838 cm −1 , 10 which was reduced or broadened in the SiC:Ge.…”

mentioning

confidence: 97%

“…Figure 2 shows the reflectance in the reststrahlen band, revealing the axial folded-transverse-optic (FTO) mode of 4H-SiC at 838 cm −1 , 10 which was reduced or broadened in the SiC:Ge. 10 The SiC:Ge reflectivity at 948 cm −1 was investigated versus the incident angle and polarization as in Fig. 10,11 The SiC:Ge with Ge= 0.07% had a broad band at 948 cm −1 that decreased to 943 cm −1 for Ge= 1.25%.…”

mentioning

confidence: 99%

Pseudomorphic SiC alloys formed by Ge ion implantation

Dashiell

Xuan

Ansorge

et al. 2004

Applied Physics Letters

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Pseudomorphic-strained layers containing from 0.07-1.25 atomic % Ge were formed by ion implantation at 1000°C into 4H-SiC substrates. X-ray diffraction revealed high crystalline quality and coherent interfaces for strains up to 1.4%. Infrared reflectivity indicated a phonon mode at 948 cm −1 , attributed to Ge implantation disorder. Annealing above 1250°C caused the disappearance of the 948 cm −1 disorder mode, and the strengthening of the phonon mode at 848 cm −1 , associated with the 4H stacking sequence. Structural measurements of the annealed samples revealed thermally stable, coherently strained layers of the 4H polytype, without precipitation, suggesting an isoelectronic Ge alloy compatible with SiC for heterostructure strained layer engineering.

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Weak phonon modes observation using infrared reflectivity for 4H, 6H and 15R polytypes

Cited by 19 publications

References 7 publications

Thermal evolution of silicon carbide electronic bands

Thermal evolution of silicon carbide electronic bands

Hybrid longitudinal-transverse phonon polaritons

Pseudomorphic SiC alloys formed by Ge ion implantation

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