Effect of indium incorporation, stimulated by UHV treatment, on the chemical, optical and electronic properties of ZnO thin film

We show the importance of powerful and complementary analysis techniques XPS (X-rays Photoelectron Spectroscopy), AES (Auger Electron Spectroscopy), and UPS (UV Photoelectron Spectroscopy) associated with PL (Photoluminescence) to investigate the chemical composition, optical emission, and electronic structure of undoped ZnO (UZO) and In-doped ZnO (IZO) thin films at the contaminated and clean states. The growth process of films on the Si substrate is achieved by ultrasonic spray pyrolysis. Both samples are submitted in the same conditions to cleaning treatment (argon ion etching followed by thermal annealing in Ultra High Vacuum UHV). The XPS and AES results display the great interest of physical UHV treatment to eliminate the contamination layer and stimulate the incorporation and oxidation of indium into the ZnO matrix. The PL measurements confirm that the UHV treatment allows the incorporation of indium into the ZnO matrix and eliminates wholly the visible emission due to hydroxyl impurities and defects such as oxygen interstitial and oxygen vacancies. The UPS technique is useful to show the electronic structure of the valence band and determine the work function, Fermi level, and the ionization potential of both samples.