| AVS 61st International Symposium & Exhibition | |
| Energy Frontiers Focus Topic | Wednesday Sessions |
| Session EN+AS+EM-WeA |
| Session: | Organic-Inorganic Interfaces for Energy |
| Presenter: | Mirella Vargas, The University of Texas at El Paso |
| Authors: | M. Vargas, The University of Texas at El Paso C.V. Ramana, The University of Texas at El Paso |
| Correspondent: | Click to Email |
Tungsten oxide (WO3) is a technologically important n-type semi-conductor that is extensively studied in the fields of electronic and opto-electronic devices. Due to its unique properties such as a high work function and high-coloration efficiency, WO3 is attractive for electrochromic and memory devices including large area information displays, smart-windows, and optical heat-mirrors. Low-dimensional structures of WO3 coupled with an ideal band gap (Eg ~ 2.8 eV) have been employed as materials for the photocatalyst driven by visible light irradiation in dye-sensitized solar cells. In addition, WO3 has also become a strong contender to replace indium-doped tin oxide or ITO thin films in transparent electrode applications. The present work is focused on WO3 thin films characterized as promising transparent conducting oxide (TCO) materials by investigating doping effects on the structural, chemical, and optical properties. The incorporation of titanium (Ti) was achievable by depositing the films through co-sputtering of W and Ti metal targets. The sputtering powers to the W and Ti were kept constant at 100 W and 50 W, respectively, while varying the growth temperature (Ts) in the range of 25-500 oC. While all the samples are optically transparent, the structural quality of Ti-doped WO3 films is dependent on Ts. Ti-doped WO3 films grown at Ts<400 oC were amorphous. A temperature of 400 oC is critical to promote the structural order and formation of nanocrystalline films in the monoclinic phase. T he optical constants and their dispersion profiles determined from spectroscopic ellipsometry indicate that there is no significant inter-diffusion at the film-substrate interface for W-Ti oxide film growth of ~40 nm. The index refraction (n) at l=550 nm vary in the range of 2.15-2.40 with a gradual increase in growth temperature. Nitrogen (N2) incorporation was made through a post-deposition anneal in an ammonia environment on WO3 films. The un-doped WO3 films grown by variable growth temperature will be annealed at high temperatures for various rates to accommodate a strong N2 incorporation. The tungsten oxynitride films will be characterized by various analytical techniques to compare the doping effects of Ti and N2 on the structural, electronic, and optical properties of WO3 thin films.