Coupling of GaN- and AlN-like longitudinal optic phonons in Ga1−xAlxN solid solutions

Abstract

Long-wavelength optical phonons of Ga1−xAlxN solid solutions have been identified in a wide compositional range by Raman spectroscopy. The A1 and E1 polar phonon frequencies evolve continuously with x from one-member crystal to the other. The same behavior seems to hold true for the silent B1 mode, which manifests itself by an interference with an unidentified continuum. Coupling of the longitudinal-optic (LO) modes associated with the two types of bonds, via the macroscopic electric field, is treated by a generalization of the dielectric model [D. T. Hon and W. L. Faust, J. Appl. Phys. 1, 241 (1973)]. This approach accounts for the observed frequencies and supports the apparent one-mode behavior of the polar LO phonons.

Interplay between GaN and AlN sublattices in wurtzite AlxGa1−xN alloys revealed by Raman spectroscopy

“…This is in contradiction to theoretical estimations, which predict that the frequency of Ga LVM should be considerably lower than that of Al LVM , i. e., very far from the A1(LO) band in AlN. 2,7 In view of its behavior upon selection rules, and the evolution with x, we believe that the feature at 705 cm Ϫ1 in Fig. 4, ͑sample with xϭ0.25͒ can be one of such in-band modes, which shows up likely from disorder activated TO scattering.…”

“…Lattice dynamics of the Al x Ga 1Ϫx N system has been widely studied along the whole compositional range by several authors, 2 though few works have focused on the range of very low Al contents (xϽ0.15). In this article, special interest is devoted to this range, where typical morphic effects caused by the alloy are already revealed.…”

Double strain state in a single GaN/AlN nanowire: Probing the core-shell effect by ultraviolet resonant Raman scattering

“…In X(−,−)X configuration, QLO mode refers to LO phonon with quasi-E 1 symmetry and is generally observed in non resonant Raman scattering spectra recorded in the X(Z,Z)X polarization configuration. [27][28][29] A weak contribution of A 1 symmetry tensor is generally admitted because of an admixture of a small A 1 component due to the aperture of the focusing lens. We believe that in the X(Y,−)X configuration, QLO phonon scattering is not clearly observed in our experiments for symmetry considerations : for phonon wave-vector perpendicular to the c-axis in wurtzite crystals, diagonal Y Y and ZZ components of the electronic susceptibility due to the intraband Fröhlich interaction are different in principle.…”

Raman scattering studies on single-crystalline bulk AlN under high pressures

“…17 The QLO frequency is often used in the literature as an approximation for the E 1 ͑LO͒ frequency. 18 The observation of the pure E 1 ͑LO͒ mode requires quasi-right angle scattering geometry 17 that is not accessible in a DAC. The colorless ͑transparent͒ single-crystalline bulk AlN used in this study was grown in a resistively heated furnace in nitrogen ambient from a sintered pure AlN source at a temperature of 2000-2200°C.…”