Surface phonon polariton of wurtzite GaN thin film grown on cc-plane sapphire substrate

In this paper, surface phonon polariton (SPP) of wurtzite structure gallium nitride (GaN) thin film grown on cc-plane sapphire (Al2O3) substrate is investigated by means of pp-polarized infrared attenuated total reflection (ATR) spectroscopy. The result showed that GaN exhibits a prominent SPP absorption peak with an asymmetric line shape at 697.5 cm−1. An additional weak and broad peak which corresponds to the longitudinal-optic (LO∥) phonon mode of GaN has also been observed. Besides that, no signature due to the SPP as well as the bulk polariton modes of the Al2O3 substrate can be detected from the ATR spectrum. The obtained experimental SPP mode of the GaN thin film is compared with the theoretical result derived by means of an anisotropy model. A reasonable agreement with an uncertainty of about 1% is obtained.