The authors performed a systematic study of the structural and electrical properties of Nb:Ti O2 thin films by varying the substrate temperature (TS) and oxygen partial pressure (P O2). Niobium is found to incorporate easily and substitutionally into titanium lattice site as indicated by its low activation energy. By increasing TS, the carrier concentration (n) increases in the same way that niobium substitution fraction (s) increases, and the mobility increases as the structural quality is improved. With increasing P O2, n decreases dramatically though s does not change considerably. This may indicate that a large number of p -type native defects form, which "kill" the electrons produced by the Nb donors. © 2007 American Institute of Physics.