Substrate Effects on Structural and Optical Properties of ZnO Thin Films Deposited by Chemical Spray Pyrolysis

Abstract

ZnO thin films deposited on various substrates including glass, quartz, and ITO (Indium Tin Oxide) coated on glass substrates have been conducted by (CSP) technique. Characterization techniques of X-ray diffraction (XRD), atomic force microscopy (AFM), UV-visible, and photoluminescence (PL) spectra measurements were performed to investigate the effects of substrate on the structural and optical properties of ZnO thin films. Samples were prepared the thickness of thin films are (80 nm) and substrate temperature kept at (400oC) in all cases. Compressed nitrogen was used as a carrier gas. The XRD results indicated that the synthesized ZnO thin films have a pure wurtzite (hexagonal phase) structure. It can be seen that the highest texture coefficient was in (002) plane . So when a good crystalline substrate like quartz is used for depositing the film, the lattice matching with the deposited film material would be better. AFM measurement showed the grain size ranging from (62-86) nm. The optical studies showed that the thin film for ITO coated glass substrate higher transmittance than glass and quartz substrate. The optical band gap for ZnO thin films have two values for the same sample, and we will note the band gap of the thin films increasing with increase the crystalline of substrate. The energy gap from photoluminescence (PL) spectra is (3.369 eV) for all samples.