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

Abstract

We use Raman scattering to investigate the composition behavior of the E 2h and A 1 (LO) phonons of In x Ga 1Àx N and to evaluate the role of lateral compositional fluctuations and in-depth strain/ composition gradients on the frequency of the A 1 (LO) bands. For this purpose, we have performed visible and ultraviolet Raman measurements on a set of high-quality epilayers grown by molecular beam epitaxy with In contents over a wide composition range (0.25 < x < 0.75). While the as-measured A 1 (LO) frequency values strongly deviate from the linear dispersion predicted by the modified random-element isodisplacement (MREI) model, we show that the strain-corrected A 1 (LO) frequencies are qualitatively in good agreement with the expected linear dependence. In contrast, we find that the strain-corrected E 2h frequencies exhibit a bowing in relation to the linear behavior predicted by the MREI model. Such bowing should be taken into account to evaluate the composition or the strain state of InGaN material from the E 2h peak frequencies. We show that in-depth strain/composition gradients and selective resonance excitation effects have a strong impact on the frequency of the A 1 (LO) mode, making very difficult the use of this mode to evaluate the strain state or the composition of InGaN material. V C 2012 American Institute of Physics.

Temperature dependence of Mg-H local vibrational modes in heavily doped InN:Mg

“…Although, as reported in Ref. 19, a residual strain is present in the samples with In concentration between 0.34 and 0.44, the results shown in Fig. 3 indicate that this has not a significant influence on the measured SAW velocities, which are well described by the simulations using the elastic constants given by Eq.…”

“…In the same figure, we have plotted the Rayleigh and Sezawa acoustic wave velocities measured at different kh values in sample A1182, which as shown in Ref. 19 corresponds to a fully relaxed In 0:75 Ga 0:25 N epilayer. As can be seen in Fig.…”

“…Growth details and characterization of these samples have been published elsewhere. 19 HRBS experiments were performed in backscattering geometry for different sagittal angles using the k 0 ¼ 514:5 nm excitation wavelength. A description of the experimental set-up can be found in Ref.…”

(Ga,In)P nanowires grown without intentional catalyst

“…It is possible to see peaks at 395 and 360 cm À 1 , they are the longitudinal (LO) and transversal (TO) optical modes, respectively. Those peaks are shifted from the peaks of pure GaP indicating that In is present [23][24][25][26][27][28]. The In content in the nanowires is dependent on the pressure of the chamber.…”

Raman and photoluminescence mapping of InxGa1−xN (x ∼ 0.4) at high pressure: Optical determination of composition and stress

“…1(b) the A 1 (LO) peak in the ambient pressure spectra of the as-grown sample excited by the 514.5 and 785 nm lines}. [9][10][11] In the ternary system under investigation, the peaks at $544 and $706 cm À1 are attributed to the high frequency E 2 (E 2 2 ) and the A 1 (LO) mode, respectively. The shoulder at $682 cm À1 , also called "S peak", 12 has been previously attributed to an alloy disorder-activated band, most probably related with the silent B 1 mode.…”