Figures

Figure 1

Experimental data (symbols), and best-fit calculation (solid lines) of from (a) -Al2O3 (c-plane), (b) undoped -GaN, (c) -Al0.17Ga0.83N, (d) -Al0.28Ga0.72N, (e) -Al0.50Ga0.50N, and (f) -AlN. Vertical arrows indicate frequencies at which resonant excitation of E1(TO) (solid arrows), and A1(LO) phonons (dotted arrows) occur. The vertical lines denote the modes of the AlN-nucleation layer (f), as these are present in spectra (b) - (e) as well. The angle of incidence is a = 72°. Spectra are to scale, but shifted for convenience by 60° each. The brackets below spectra (a) indicate the sapphire A2u phonon frequencies (TO: solid, LO: dotted). See also Figure 2. The sapphire phonon modes are given in the text.

Figure 2

Same as Figure 1 for cos. The brackets below spectra (a) indicate the Eu modes of sapphire. See text for further explanation.

Figure 3

Experimental data (symbols), and best-fit calculation (solid lines) of from differently Si-doped n-type -GaN films. Vertical lines indicate the E1(TO), and A1(LO) phonon frequencies of the GaN epilayer (dash-dotted), and the AlN buffer layer (dotted).

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