Effect of pressure on the Raman scattering of wurtzite AlN (original) (raw)
Related papers
Raman scattering study of wurtzite and rocksalt InN under high pressure
Physical Review B, 2006
Indium nitride under high pressure ͑up to 50 GPa͒ was analyzed by means of Raman spectroscopy. The wurtzite to rocksalt phase transition was evidenced at the pressure of 13.5± 0.5 GPa and the pressure dependence of vibration modes of both structures was investigated, leading to the determination of linear pressure coefficients and mode Grüneisen parameters. Influence of the pressure dependence of the energy gap on the spectra intensity is also discussed.
Physical Review B, 2013
We present an experimental and theoretical lattice-dynamical study of InN at high hydrostatic pressures. We perform Raman scattering measurements on five InN epilayers, with different residual strain and free electron concentrations. The experimental results are analyzed in terms of ab initio lattice-dynamical calculations on both wurtzite InN (w-InN) and rocksalt InN (rs-InN) as a function of pressure. Experimental and theoretical pressure coefficients of the optical modes in w-InN are compared, and the role of residual strain on the measured pressure coefficients is analyzed. In the case of the LO band, we analyze and discuss its pressure behavior considering the double-resonance mechanism responsible for the selective excitation of LO phonons with large wave vectors in w-InN. The pressure behavior of the L − coupled mode observed in a heavily doped n-type sample allows us to estimate the pressure dependence of the electron effective mass in w-InN. The results thus obtained are in good agreement with k • p theory. The wurtzite-to-rocksalt phase transition on the upstroke cycle and the rocksalt-to-wurtzite backtransition on the downstroke cycle are investigated, and the Raman spectra of both phases are interpreted in terms of DFT lattice-dynamical calculations.
High-pressure Raman scattering in wurtzite indium nitride
Applied Physics Letters, 2011
We perform Raman-scattering measurements at high hydrostatic pressures on c-face and a-face InN layers to investigate the high-pressure behavior of the zone-center optical phonons of wurtzite InN. Linear pressure coefficients and mode Grüneisen parameters are obtained, and the experimental results are compared with theoretical values obtained from ab initio lattice-dynamical calculations. Good agreement is found between the experimental and calculated results.
Phonon dispersion and Raman spectra of wurtzite InAs under pressure
The authors have systematically studied the vibrational properties of wurtzite InAs at high pressure within the Density Functional Theory scheme. It is found that pressure significantly affects the phonon dispersion curves and Raman spectra. We observed an indication of phase transition for WZ-InAs at about 10 GPa. The elastic constants calculation show mechanical stability for WZ-InAs. The calculated values of structural parameters are in good agreement with available data. There is a quadratic increase in optical modes with pressure while the LO–TO splitting and effective charge decrease linearly with pressure.
Journal of Applied Physics, 2002
The large frequency shift displayed by the longitudinal optical ͑LO͒ phonons A1(LO) and E1(LO) when going from GaN to AlN promises an accurate determination of the composition in Al x Ga 1Ϫx N bulk layers by Raman spectroscopy. However, this determination is affected by a large uncertainty for low Al mole fractions (xϽ0.20), due to the broadened spectral line shape exhibited by these modes. A detailed study of Raman spectra recorded on layers with xϽ0.27, grown either on sapphire or on silicon substrates, has been performed in order to elucidate the origin of that broadening. The influence on the A1(LO) line shape of the sapphire substrate modes, compositional inhomogeneities, residual strain, and those effects inherent to the lattice dynamics of ternary alloys, is analyzed. We conclude that the broadening is caused by intrinsic inhomogeneities of the microscopic polarization fields resulting from alloying. This effect is usually obscured in other III-V compounds, such as arsenides or phosphides, due to their considerably lower LO-transverse optical splitting.
High pressure infrared and X‐ray Raman studies of aluminum nitride
physica status solidi (b), 2013
We performed the first reported static high pressure studies of the wide bandgap material aluminum nitride (AlN) using mid‐infrared (IR) and X‐ray Raman spectroscopy (XRS) up to 35 and 33 GPa, respectively, in a diamond anvil cell (DAC) at ambient temperature. For the first (IR) experiment, we employed a synchrotron IR source. Below the wurtzite (WZ) → rock salt (RS) phase transition, the IR spectra shift monotonically toward higher energy with pressure. Above this phase transition, the spectral multiplet stabilizes and then shifts toward lower energies suggesting a weakening of the bonding with pressure. To better examine the bonding changes we utilized the 16 ID‐D undulator beamline at the Advanced Photon Source (APS) for the second experiment. The spectrometer collected photons with ∼410 eV energy loss (nitrogen edge) with respect to incident beam energy near 10 keV. The sample commenced in the WZ phase and upon pressurization above ∼15 GPa, the sample converted into the high pre...
Raman scattering and x-ray-absorption spectroscopy in gallium nitride under high pressure
Physical Review B, 1992
Gallium nitride was studied by Raman scattering and x-ray-absorption spectroscopy up to 60 GPa. A high-pressure structural phase transition was observed in gallium nitride at 47 GPa by means of Raman scattering and x-ray-absorption spectroscopy. We also report the direct determination of the bulk modulus Bo of this compound {24S GPa). Gruneisen parameters of the four observed phonon modes were established. The transition pressure is compared with existing calculations.
Pressure dependence of the dielectric and lattice-dynamical properties of GaN and AlN
Physical Review B
We present ab initio calculations of the structural, dielectric, and lattice-dynamical properties of zinc-blende and wurtzite GaN and AlN under hydrostatic pressure, based on a plane-wave pseudopotential method within the density-functional theory. The calculated volume dependence is related to pressure by means of the Vinet equation of state. A linear-response approach to the density-functional theory is used to derive Born effective charges, dielectric constants, and phonon frequencies. The static ionicities, the dynamic charges, and the dielectric constants are found to decrease with pressure, whereas the phonon frequencies show an increasing longitudinal-transverse splitting. The softening behavior of the low-frequency E 2 mode and of the corresponding TA͑L͒ mode is related to strengths of the covalent and ionic forces. Our results are in agreement with recent Raman measurements.
High-pressure Raman spectroscopy study of wurtzite ZnO
Physical Review B, 2002
The high pressure behavior of optical phonons in wurtzite zinc oxide (w-ZnO) has been studied using room temperature Raman spectroscopy and ab-initio calculations based on a plane wave pseudopotential method within the density functional theory. The pressure dependence of the zonecenter phonons (E2, A1 and E1) was measured for the wurtzite structure up to the hexagonal→cubic transition near 9 GPa. Above this pressure no active mode was observed. The only negative Grüneisen parameter is that of the E low 2 mode. E1(LO) and (TO) frequencies increase with increasing pressure. The corresponding perpendicular tensor component of the Born's transverse dynamic charge e * T is experimentally found to increase under compression like e * T (P) = 2.02 + 6.4 • 10 −3 .P whereas calculations give e * T (P) = 2.09−2.5•10 −3 .P (in units of the elementary charge e, P in GPa). In both cases, the pressure variation is small, indicating a weak dependence of the bond ionicity with pressure. The pressure dependence of the optical mode energies is also compared with the prediction of a model that treats the wurtzite-to-rocksalt transition as an homogeneous shear strain. There is no evidence of anomaly in the E2 and A1 modes behavior before the phase transition.