Measurement of Ionization Energies of Nitrogen in 4H-SiC by Traveling-Wave Method

Takase, Toru; Sakaino, Masamichi; Sun, Yong; Miyasato, Tatsuro

doi:10.7567/jjap.52.091301

Cited by 3 publications

(4 citation statements)

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“…The average activation energy E A of the nitrogen impurity band for all chips studied of about 40 meV is somewhat lower than the range of values of the donor binding energy given for an isolated donor in the literature of 50 to 100 meV. [17][18][19][20] The reason is that the broadening of the impurity band due to the interacting donor wave functions causes an effective reduction of the donor binding energy which is proportional to the donor density to the power 1/3. 9, [27][28][29] Raman spectroscopy can explore the coupling between phonons and free electrons to extract electronic transport parameters.…”

Section: Resultsmentioning

confidence: 58%

“…The isolated nitrogen donor has a depth between 50 and 100 meV depending on the local site. [17][18][19][20] Thus, the onset of the saturation is about expected at about 600 K. The onset temperature of the intrinsic region in SiC is way above the highest temperature of 700 K where we performed experiments due to a band gap energy E CB -E VB ¼ 3 eV for 4H-SiC in the temperature range studied. 21 Thus, only the free carriers in the CB contribute to the electric transport up to 300 K, i.e., the temperature range covers almost solely the freeze-out region, which is the justification for using a one-band Drude model in such a scenario.…”

Section: Resultsmentioning

confidence: 91%

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Validation of Raman spectroscopy as a tool for mapping transport parameters in inhomogeneous N‐doped 4H‐SiC

Hergert

Elm

Klar

2023

J Raman Spectroscopy

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We assess Raman spectroscopy as a tool for fast and non‐invasive mapping of charge carrier density and carrier mobility in inhomogeneously doped 4H‐SiC. For this purpose, we compare values of these transport parameters obtained by magneto‐transport and Raman measurements of N‐doped 4H‐SiC. The comparison is not straightforward. The effective charge density and mobility, which are obtained from resistivity and Hall measurements by employing the commonly used effective one‐band model, deviate from the values extracted by applying the established line‐shape models for describing the longitudinal optical phonon coupled (LOPC) modes in the Raman spectra. Differentiating between free and localized carriers in the framework of a three‐band transport model confirms that only the free charge carriers in the conduction band of N‐doped 4H‐SiC contribute to the LOPC Raman signal and their density agrees well with that obtained by the line shape analysis. The agreement of the mobility values is good keeping in mind that different frequencies of the applied electric fields are used in the two approaches, i.e., dc‐transport measurements at 0 Hz and ac‐fields of the exciting laser at about 500 THz. Moreover, the excitation of electrons into the conduction band by the laser, which is inherent to the Raman experiment, causes differences in the temperature dependence of the carrier density compared with the electrical transport data.

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Section: Resultsmentioning

confidence: 58%

Section: Resultsmentioning

confidence: 91%

Validation of Raman spectroscopy as a tool for mapping transport parameters in inhomogeneous N‐doped 4H‐SiC

Hergert

Elm

Klar

2023

J Raman Spectroscopy

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“…51,52 We also must point out that when Z L is much less than Z s the current passing through the sample is constant, and energy loss of the travelingwave is inversely proportional to conductivity of the sample. On the other hand, when Z L is much larger than Z s the electric field strength in the sample is constant, and the energy loss is proportional to conductivity of the sample.…”

Section: -5mentioning

confidence: 99%

Coupling behaviors of graphene/SiO2/Si structure with external electric field

2017

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A traveling electric field in surface acoustic wave was introduced into the graphene/SiO2/Si sample in the temperature range of 15 K to 300 K. The coupling behaviors between the sample and the electric field were analyzed using two parameters, the intensity attenuation and time delay of the traveling-wave. The attenuation originates from Joule heat of the moving carriers, and the delay of the traveling-wave was due to electrical resistances of the fixed charge and the moving carriers with low mobility in the sample. The attenuation of the external electric field was observed in both Si crystal and graphene films in the temperature range. A large attenuation around 190 K, which depends on the strength of external electric field, was confirmed for the Si crystal. But, no significant temperature and field dependences of the attenuation in the graphene films were detected. On the other hand, the delay of the traveling-wave due to ionic scattering at low temperature side was observed in the Si crystal, but cannot be detected in the films of the mono-, bi- and penta-layer graphene with high conductivities. Also, it was indicated in this study that skin depth of the graphene film was less than thickness of two graphene atomic layers in the temperature range.

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“…S6 in Ref. 39) because of a larger number of typical nitrogen donors ionization at k and h sites at 120 and 60 meV [49], respectively, with increasing temperatures. This paves the way for space agencies to employ 4H SiC based integrated circuits to probe the surface of Venus, where the temperature is ≈730 K [21].…”

mentioning

confidence: 97%

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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Measurement of Ionization Energies of Nitrogen in 4H-SiC by Traveling-Wave Method

Cited by 3 publications

References 46 publications

Validation of Raman spectroscopy as a tool for mapping transport parameters in inhomogeneous N‐doped 4H‐SiC

Validation of Raman spectroscopy as a tool for mapping transport parameters in inhomogeneous N‐doped 4H‐SiC

Coupling behaviors of graphene/SiO2/Si structure with external electric field

Thermal evolution of silicon carbide electronic bands

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