Raman Scattering Study of InGaN Grown by Metalorganic Vapor Phase Epitaxy on (0001) Sapphire Substrates

Abstract

We have studied the asymmetric broadening of the Raman spectra of In x Ga1-x N grown on sapphire substrates with the aid of the spatial correlation model. The asymmetric broadening of the E2 phonon mode is enhanced in the region of immiscibility by increasing the indium molar fraction. The correlation length, which corresponds to the decay length of the E2 phonon mode, was estimated for the first time. It was on the order of 6–10 nm, which is on the same order of magnitude as the size of the columnar structure suggested by transmission electron microscope analyses.

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

“…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.…”

“…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.…”

“…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.…”

Direct evidence for strain inhomogeneity in InxGa1−xN epilayers by Raman spectroscopy

“…10 This Raman line shows a low frequency tail, which we observed on other surface relaxed samples. 2,4,5,15 However, its dependence on the indium content x is far from being established. 6 Actually, this tail vanishes after etching, supporting the idea that it can be related with the near surface region.…”

Fabrication and improvement of nanopillar InGaN / GaN light-emitting diodes using nanosphere lithography

“…The E 2 phonon-mode peak shift toward lower energy affirms that strain relaxation has taken place in the InGaN∕GaN MQWs. 22,28,29 To further understand the effects of different treatments, we performed x-ray photoelectron spectroscopy (XPS) measurements using a Thermo K-Alpha system from Thermo Scientific with an Al K-Alpha source. The pass energy was set to 200.0 eV for the survey scan and 50.0 eV for high resolution scans.…”