Ultraviolet Raman study of A1(LO) and E2 phonons in InxGa1−xN alloys

Abstract

We report on ultraviolet Raman spectroscopy of InxGa1−xN thin films grown on sapphire by metal-organic chemical vapor deposition. The A1(LO) and E2 phonon mode behavior was investigated over a large compositional range (0<x<0.50). Compelling evidence is presented for one-mode behavior for the A1(LO) phonon, and data suggestive of two-mode behavior are presented for the E2 phonon.

Raman scattering by the E2h and A1(LO) phonons of InxGa1−xN epilayers (0.25 < x < 0.75) grown by molecular beam epitaxy

“…In Ref. 10, a similar observation in In x Ga 1Àx N films with x < 0.5 led the authors to conclude that the E 2h mode exhibits a two-mode behavior, as occurs in Al x Ga 1Àx N. 40 In the present work, using data over the whole composition range, we conclude that the E 2h mode of In x Ga 1Àx N exhibits a one-mode behavior and suffers a strong bowing effect. Very recent work by Kim et al 21 seems to point in the same direction.…”

“…While the modified random-element isodisplacement (MREI) model 25 predicts that the frequency of both modes varies linearly from those of the two binary endmembers (GaN and InN), some authors have measured E 2h frequencies that seem to exhibit a significant bowing in relation to the linear frequency dependence. 9,10,13,21 On the other hand, strong deviations from the linear behavior have also been observed for the A 1 (LO) polar mode of bulk InGaN (see for instance the data over the whole composition range reported in Ref. 16.…”

“…In contrast, we find that the strain-corrected E 2h frequencies are redshifted over the whole composition range in relation to the linear behavior, in agreement with previous observations on Ga-rich samples. 9,10 The possible role of lateral compositional fluctuations and in-depth strain/composition gradients on the frequency behavior of the A 1 (LO) mode of InGaN is analyzed and discussed.…”

“…3 for a review on III-V alloys). Numerous studies have been devoted to study the vibrational properties of hexagonal InGaN thin films [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] and InGaN/GaN quantum wells. [22][23][24] Although it is well accepted that both the A 1 (LO) and the E 2h phonon modes of InGaN display a one-mode behavior, 15,16 there are still open questions regarding the behavior of the optical phonons in the InGaN alloy.…”

Indium Distribution within InxGa1?xN Epitaxial Layers: A Combined Resonant Raman Scattering and Rutherford Backscattering Study

“…exhibits only one set of longitudinal optical (LO) and transverse optical (TO) phonons, whose frequencies vary almost linearly with compositional changes. Due to the lack of good quality samples for a wide range of composition, the A 1 (LO) phonon frequency dependence on the indium content x is not yet well-established and different behaviors can be found in the literature [4][5][6]. In some cases the observed asymmetrical band shape leads to an uncertainty on the phonon frequency at the Brillouin center zone.…”