Band-gap energies, free carrier effects, and phonon modes in strained GaNAs/GaAs and GaNAs/InAs/GaAs superlattice heterostructures measured by spectroscopic ellipsometry

2001 ◽  
Vol 89 (1) ◽  
pp. 294-305 ◽  
Author(s):  
J. Šik ◽  
M. Schubert ◽  
G. Leibiger ◽  
V. Gottschalch ◽  
G. Wagner
Keyword(s):  
Band Gap ◽  
Spectroscopic Ellipsometry ◽  
Free Carrier ◽  
Phonon Modes

scholarly journals Resonance and antiresonance in Raman scattering in GaSe and InSe crystals

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
M. Osiekowicz ◽  
D. Staszczuk ◽  
K. Olkowska-Pucko ◽  
Ł. Kipczak ◽  
M. Grzeszczyk ◽  
...  
Keyword(s):  
Raman Scattering ◽  
Temperature Effect ◽  
Band Gap ◽  
Raman Spectra ◽  
Quantum Interference ◽  
Optical Band Gap ◽  
Phonon Coupling ◽  
Phonon Modes ◽  
Electron Phonon Coupling ◽  
Resonant Raman

AbstractThe temperature effect on the Raman scattering efficiency is investigated in $$\varepsilon$$ ε -GaSe and $$\gamma$$ γ -InSe crystals. We found that varying the temperature over a broad range from 5 to 350 K permits to achieve both the resonant conditions and the antiresonance behaviour in Raman scattering of the studied materials. The resonant conditions of Raman scattering are observed at about 270 K under the 1.96 eV excitation for GaSe due to the energy proximity of the optical band gap. In the case of InSe, the resonant Raman spectra are apparent at about 50 and 270 K under correspondingly the 2.41 eV and 2.54 eV excitations as a result of the energy proximity of the so-called B transition. Interestingly, the observed resonances for both materials are followed by an antiresonance behaviour noticeable at higher temperatures than the detected resonances. The significant variations of phonon-modes intensities can be explained in terms of electron-phonon coupling and quantum interference of contributions from different points of the Brillouin zone.

scholarly journals Temperature-dependent optical and vibrational properties of PtSe2 thin films

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
Desman P. Gulo ◽  
Han Yeh ◽  
Wen-Hao Chang ◽  
Hsiang-Lin Liu
Keyword(s):  
Thin Films ◽  
Band Gap ◽  
Room Temperature ◽  
Near Infrared ◽  
Technological Development ◽  
Phonon Modes ◽  
Research Attention ◽  
Practical Applications ◽  
Infrared Frequency Range ◽  
Indirect Band Gap

Abstract PtSe2 has received substantial research attention because of its intriguing physical properties and potential practical applications. In this paper, we investigated the optical properties of bilayer and multilayer PtSe2 thin films through spectroscopic ellipsometry over a spectral range of 0.73–6.42 eV and at temperatures between 4.5 and 500 K. At room temperature, the spectra of refractive index exhibited several anomalous dispersion features below 1000 nm and approached a constant value in the near-infrared frequency range. The thermo-optic coefficients of bilayer and multilayer PtSe2 thin films were (4.31 ± 0.04) × 10−4/K and (–9.20 ± 0.03) × 10−4/K at a wavelength of 1200 nm. Analysis of the optical absorption spectrum at room temperature confirmed that bilayer PtSe2 thin films had an indirect band gap of approximately 0.75 ± 0.01 eV, whereas multilayer PtSe2 thin films exhibited semimetal behavior. The band gap of bilayer PtSe2 thin films increased to 0.83 ± 0.01 eV at 4.5 K because of the suppression of electron–phonon interactions. Furthermore, the frequency shifts of Raman-active Eg and A1g phonon modes of both thin films in the temperature range between 10 and 500 K accorded with the predictions of the anharmonic model. These results provide basic information for the technological development of PtSe2-based optoelectronic and photonic devices at various temperatures.

scholarly journals Free-carrier effects and optical phonons in GaNAs/GaAs superlattice heterostructures measured by infrared spectroscopic ellipsometry

2000 ◽  
Vol 5 (1) ◽  
Author(s):  
J. Šik ◽  
M. Schubert ◽  
T. Hofmann ◽  
V. Gottschalch
Keyword(s):  
Buffer Layer ◽  
Spectroscopic Ellipsometry ◽  
Nitrogen Concentration ◽  
Free Carrier ◽  
Strong Increase ◽  
Angle Of Incidence ◽  
Surface Polariton ◽  
Infrared Spectroscopic ◽  
Gaas Buffer Layer ◽  
Undoped Gaas

The infrared-optical properties of GaAs/GaNxAs1−x superlattice (SL) heterostructures (0 < x < 3.3%) are studied by variable angle-of-incidence infrared spectroscopic ellipsometry (IRSE) for wavenumbers from 250 cm−1 to 700 cm−1. The undoped SL structures where grown on top of a 300 nm thick undoped GaAs buffer layer on Te-doped (001) GaAs substrates by metal-organic vapor phase epitaxy (MOVPE). We observe the well-known Berreman-polariton effect within the GaAs LO-phonon region. We further observe a strong polariton-like resonance near the coupled longitudinal-optical plasmon-phonon frequency of the Te-doped substrate at 306 cm−1. For analysis of the IRSE data we employ the harmonic oscillator dielectric function model and the Drude model for free-carrier response. The additional resonance feature is explained by pseudo surface polariton (PSP) interface modes between the Te-doped GaAs and the undoped GaAs buffer layer / SL film. We find that the PSP modes are extremely sensitive to free-carrier properties within the SL structures, and we obtain a strong increase in free-carrier concentration within the GaNAs SL sublayers with increasing x from analysis of the IRSE data. We further observe the localized vibrational modes of nitrogen at 470 cm−1 in the GaNxAs1−x SL sublayers with a polar strength that increases linearly with x, and which can be used to monitor the nitrogen concentration in GaNxAs1−x.

Phonons and Free Carriers in a Strained Hexagonal GaN-AlN Superlattice Measured by Infrared Ellipsometry and Raman Spectroscopy

1999 ◽  
Vol 595 ◽  
Author(s):  
M. Schubert ◽  
A. Kasic ◽  
T.E. Tiwald ◽  
J.A. Woollam ◽  
V. Harle ◽  
...  
Keyword(s):  
Carrier Mobility ◽  
Free Carrier ◽  
Phonon Modes ◽  
Lateral Mobility ◽  
Free Carriers ◽  
Organic Vapor ◽  
Infrared Ellipsometry ◽  
Order Of Magnitude ◽  
Metal Organic ◽  
Vertical Mobility

AbstractPhonon and free-carrier effects in a strained hexagonal (α) {GaN}l-{AlN}m superlattice (SL) heterostructure (l = 8 nm, m = 3 nm) are studied by infrared spectroscopic ellipsometry (IRSE) and micro (µ)-Raman scattering. Growth of the heterostructures was performed by metal-organic vapor phase epitaxy (MOVPE) on (0001) sapphire. An unstrained 1 µm-thick α-GaN layer was deposited prior to the SL. SL phonon modes are identified combining results from both IRSE and µ-Raman techniques. The shift of the GaN-sublayer phonon modes is used to estimate an average compressive SL stress of σxx ∼ - 4.3 GPa. The IRSE data reveal a free-carrier concentration of ne ∼ 5×1018 cm−3 within the undoped SL GaN-sublayers. According to the vertical carrier confinement, the free-carrier mobility is anisotropic, and the lateral mobility ( µ⊥ ∼ 400 cm2/Vs, polarization E⊥c-axis) exceeds the vertical mobility (µ∥ ∼ 24 cm2/Vs, E∥c) by one order of magnitude.

The thickness-dependent band gap and defect features of ultrathin ZrO2 films studied by spectroscopic ellipsometry

2016 ◽  
Vol 18 (4) ◽  
pp. 3316-3321 ◽  
Author(s):  
Ji-Ping Xu ◽  
Rong-Jun Zhang ◽  
Yuan Zhang ◽  
Zi-Yi Wang ◽  
Lei Chen ◽  
...  
Keyword(s):  
Band Gap ◽  
Spectroscopic Ellipsometry ◽  
Point Method ◽  
Thickness Effect

The thickness effect on the band gap and defect features of ultrathin ZrO2 films is revealed by spectroscopic ellipsometry through the point-by-point method.

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