In the present work the Raman scattering spectra and infrared reflection spectra of GaN thin films with the thickness of 2-2.5 mm, grown by MOCVD method on sapphire substrates, oriented along the c axis, are investigated. The GaN thin films were doped with Si. AFM studies show the smooth surface of the GaN thin films. In the Raman spectra of the GaN thin films an E₂ phonon mode and an A₁(LO) phonon mode are revealed. In the infrared spectra an A₁(TO) mode and an A₁(LO) mode of wurtzite GaN are detected. The A₁(LO) mode is a function of the free electron density. From the known relationships, the density of free electrons was calculated from the A₁(LO) peak frequency. The presence of mechanical strain in the thin films and the substrate is shown. The experimental results of the studies of the Si-doped GaN thin films grown by MOCVD method, show the wurtzite hexagonal structure of the GaN thin films with the density of free electrons within 10¹⁸ – 10¹⁹ cm^-3.

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1. Influence of heavily doped n-Si(111) substrate on optical properties of the AlN thin films