Figure 2

Experimental data (symbols), and best-fit calculation (solid lines) of from GaAs/GaN_xAs_1-x-SL heterostructures (See Table 1). Vertical lines indicate the GaAs _TO (TO₁) and _LO (LO₁) frequencies. The Berreman-polariton effect above the GaAs LO₁ frequency causes distinct resonance features in all samples. The upper-branch PSP⁺ mode is excited near 306cm^-1 between the n-type GaAs substrate and the undoped GaAs buffer layer / SL heterostructure. See also Figure 3. The angle of incidence is _a = 70°. Spectra are to scale, but shifted for convenience by 20° each. The PSP⁺ resonance becomes washed out for higher nitrogen contents due to screening of the incident electromagnetic field components within the GaN_xAs_1-x-SL sublayers by free carriers, which concentrate within the GaN_xAs_1-x-SL sublayers. At TO₂, the Ga-N sublattice vibration is detected within the IRSE spectra. See also Figure 4.

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