Figure 1

Experimental data (symbols), and best-fit calculation (solid lines) of from (a) -Al₂O₃ (c-plane), (b) undoped -GaN, (c) -Al_0.17Ga_0.83N, (d) -Al_0.28Ga_0.72N, (e) -Al_0.50Ga_0.50N, 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 A_2u phonon frequencies (TO: solid, LO: dotted). See also Figure 2. The sapphire phonon modes are given in the text.

(click for full image)

top        text     Figure 2        endnotes

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