Study of birefringence inside nanocrystalline Zinc Oxide thin films using terahertz spectroscopy

Abstract

We present experimental characterizations of nanocrystalline Zinc Oxide (ZnO) thin films in far-infrared (terahertz) frequency region using terahertz time-domain spectroscopy. A time dependent profile, frequency dependent transmission coefficient, refractive index, absorption coefficient and optical density of ZnO thin films are measured in the terahertz regime. A birefringence is observed as a result of TO–LO phonon splitting took place in the ZnO deposited at 400 °C substrate temperature, while at low substrate temperature of 200 °C there is no sign of birefringence. Thus, it can be clearly evidenced that the presence of birefringence in ZnO is correlated with crystallinity exists inside of the thin films. Absorption behaviour of ZnO nano-crystalline thin films shows the potential use of it for future THz photonics devices. RF magnetron sputtering is the key for the deposition of nanocrystalline ZnO thin films on Si (100) substrate at different temperatures. The X-ray diffraction pattern of ZnO thin films were confirmed the formation of wurtzite hexagonal structure and nanocrystalline nature of the deposited ZnO thin films.