IR emission and electrical conductivity of Nd/Nb-codoped TiOx (1.5 < x < 2) thin films grown by pulsed-laser deposition

Abstract

The effect of the co-doping with Nd and Nb on electrical and optical properties of TiOx films is reported. The role of oxygen vacancies on the physical properties is also evidenced. The films are grown by pulsed-laser deposition onto (001) sapphire and (100) silicon substrates. The substrate temperature was fixed at 700°C. To obtain either stoichiometric (TiO2) or highly oxygen deficient (TiOx with x<1.6) thin films, the oxygen partial pressure was adjusted at 10−1 and 10−6mbar, respectively. 1%Nd-1%Nb, 1%Nd-5%Nb and 5%Nd-1%Nb co-doped TiO2 were used as bulk ceramic target. Composition, structural and morphological properties of films determined by Rutherford backscattering spectroscopy, X-ray diffraction and scanning electron microscopy, are correlated to their optical (UV–vis transmission and photoluminescence) and electrical properties (resistivity at room temperature). The most intense Nd3+ emission in the IR domain is obtained for stoichiometric films. Codoping Nd-TiOx films by Nb5+ ions is found to decrease the photoluminescence efficiency. The oxygen pressure during the growth allows to tune the optical and electrical properties: insulating and highly transparent (80% in the visible range) Nd/Nb codoped TiO2 films are obtained at high oxygen pressure, while conductive and absorbent films are grown under low oxygen pressure (10−6mbar).