Band gaps and phonons of quasi-bulk rocksalt ScN
| Authors | |
|---|---|
| Year of publication | 2024 |
| Type | Article in Periodical |
| Magazine / Source | Physical Review Materials |
| MU Faculty or unit | |
| Citation | |
| web | https://journals.aps.org/prmaterials/pdf/10.1103/PhysRevMaterials.8.L071601 |
| Doi | http://dx.doi.org/10.1103/PhysRevMaterials.8.L071601 |
| Keywords | Dielectric properties; Phonons; Ellipsometry; Optical techniques; Raman spectroscopy |
| Description | ScN is an emerging transition metal nitride with unique physical properties arising from the d electrons of Sc. In this letter, we present the results of optical characterization techniques: spectroscopic ellipsometry, Raman spectroscopy, and photoluminescence measurements of a 40-mu m-thick fully relaxed, and only weakly n-type doped (n = 1.2 x 10(18) cm(-3)) ScN film deposited by halide vapor phase epitaxy (HVPE) on r-sapphire substrate. Spectroscopic ellipsometry yields an indirect band gap of 1.1 eV, while the lowest direct interband transition is observed at E-g,E-opt = 2.16 eV in the dielectric function. A broad luminescence feature at 2.15 eV is observed, matching this transition. We derive an estimate for the exciton binding energy (E-bX approximate to 14 meV) as well as the Born effective charges Z(Sc)*= -Z(N)(& lowast;) = 3.81. In the infrared spectral region, we observe a strong phonon and a weak plasmon absorption. We precisely determine the transverse optical (TO) phonon eigenfrequency (omega(TO) = 340.7 cm(-1)), the high frequency dielectric constant (epsilon(infinity) = 8.3), and the static dielectric constant (estat = 29.5). Raman measurements using various excitation energies show resonant multiphonon scattering up to 6LO [sixth-order overtone for longitudinal optical (LO) phonons] for excitation above the optical band gap (E-Laser > E-g,E-opt), where the allowed 2LO scattering is the dominant scattering mechanism for all excitation energies. Their characteristic parameters determined from Lorentzian line shape fitting yield omega(LO) = 684.5 cm-1 and an increased broadening for higher LO scattering order n. |
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