Infrared reflectance characterization of porous GaN thin films on sapphire substrate using factorized-Rayleigh model

Abstract The surface morphology dependence of porous gallium nitride (PGaN) thin film on infrared (IR) dielectric response was investigated using s-polarized IR reflectance technique. Porosity-induced resonances, namely, Frohlich modes, were observed in the reststrahlen region of PGaN. Several phenomenological effective medium theories (EMTs), i.e., Maxwell Garnett, Bruggeman, Looyenga, Lichtenecker, and Rayleigh (Ra) models, were used to simulate the dielectric function and Frohlich modes of PGaN. Among the EMTs, only the Ra model successfully predicts all resonant features that originated from Frohlich modes. Finally, the Ra model is reformulated in factorized form to take into account the damping of Frohlich modes and Frohlich-plasmon coupling. Given the good fitness of experimental and simulated spectra and with the reasonable prediction of Frohlich modes, factorized-Ra model is determined to be the most appropriate EMT to describe the IR dielectric response of PGaN with cylindrical air hole.