Some studies on semiconductorheter ojunction
systems have been made in order to improve the
photocatalytic efficiency [5]. In the studies, photocatalytic
efficiency was thought to be improved in
heterogeneous semiconductor systems because the
recombination of photogenerated charge carriers
might be suppressed due to the charge separation
into the different types of semiconductor particles;
TiO2/WO3 [6,7], CdS/TiO2 [6], TiO2/ZnO [8], and TiO2/SnO2 [9] systems have been investigated as
particle, composite film, stacks and so on. Still, the
carriers’ behavior at the interface and in each
semiconductormate rial is an open question.