Polarization dependent infrared reflectivity studies of Si-doped MOCVD grown GaN/Sapphire epilayers

Comprehensive experimental and theoretical studies are reported on the infrared reflectance (IRR)/transmittance (IRT) spectra to empathize the vibrational and structural properties of Si-doped GaN films grown on sapphire substrate using metal-organic chemical vapor deposition technique. Systematic analysis of the IRR/IRT spectra is achieved in the framework of a 4 × 4 transfer matrix methodology by meticulously including both the surface roughness and effective transition layer. With careful simulations, we have demonstrated that it is possible to achieve a very good fit to the polarization dependent reflectivity spectra of Si-doped GaN/Sapphire – allowing to ascertain film thickness d, charge carrier concentration N, root-mean squared roughness and many other parameters. In the context of Berreman effect, our investigations of IRT spectra for an ultrathin Si-doped GaN film in the oblique geometry has provided a direct evidence of identifying the optical phonons and coupled plasmon-longitudinal-optical phonon modes, in good agreement with the IRR and Raman scattering spectroscopy (RSS) data. From these results, we strongly believe that the measurements of IRT spectra in obliquely incident radiation should be considered as a complementary tool to the RSS for epitomizing doped III-Ns and/or any other ultrathin films of technologically important compound semiconductor materials