Effective electron mass and phonon modes in n-type hexagonal InN -: art. no. 115206

Infrared spectroscopic ellipsometry and micro-Raman scattering are used to study vibrational and electronic properties of high-quality hexagonal InN. The 0.22-mum-thick highly n-conductive InN film was grown on c-plane sapphire by radio-frequency molecular-beam epitaxy. Combining our results from the ellipsometry data analysis with Hall-effect measurements, the isotropically averaged effective electron mass in InN is determined as 0.14m(0). The resonantly excited zone center E-1(TO) phonon mode is observed at 477 cm(-1) in the ellipsometry spectra. Despite the high electron concentration in the film, a strong Raman mode occurs in the spectral range of the unscreened A(1)(LO) phonon. Because an extended carrier-depleted region at the sample surface can be excluded from the ellipsometry-model analysis, we assign this mode to the lower branch of the large-wave-vector LO-phonon-plasmon coupled modes arising from nonconserving wave-vector scattering processes. The spectral position of this mode at 590 cm(-1) constitutes a lower limit for the unscreened A(1)(LO) phonon frequency.