Photoelecfrochemical Study of Thin Anatase 1102 Films Prepared by Metallorganic Chemical Vapor Deposition

Thin films of Ti02 have been prepared by metallorganic chemical vapor deposition. The resulting anatase films are highly resistive. By electrochemical doping, the donor density can easily be raised by two orders of magnitude, resulting in a conducting film. From optical and photocurrent measurements, an indirect bandgap of 3.26 eV is derived for poly-. crystalline anatase films. Electrolyte electroreflection reveals a direct optical transition of anatase at 3.8 eV. The anatase electrodes can be sensitized by zinc carboxyphenyl porphyrin. Infroduction Thin films of Ti02 have found widespread application. For instance, they are used as antireflection coatings,' transparent conductors,2 dielectrics,3 electrochromic films,4 and photoelectrodes.' ' Titanium dioxide is also used as a "self-cleaning " coating on windows and tiles.9 Organic pollutants on Ti02 surfaces are decomposed upon low-intensity ultraviolet (UV) radiation, and also bacteria are removed. Ti02 has an excellent chemical stability an