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

Highlights: • Nd/Nb-codoped TiO₂ PLD films are electrically insulating and transparent in the UV visible NIR spectral domain. • Nd/Nb-codoped oxygen deficient TiO_x (x ≈ 1.5) films are conductive and absorbent. • IR emission of Nd³⁺ in codoped TiO_x films is quenched due to oxygen deficiency. • High Nb-doping rate decreases the IR emission of Nd³⁺ in Nd/Nb-codoped TiO₂ films. - Abstract: The effect of the co-doping with Nd and Nb on electrical and optical properties of TiO_x 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 (TiO_x with x < 1.6) thin films, the oxygen partial pressure was adjusted at 10⁻¹ and 10⁻⁶ mbar, 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-TiO_x 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 (10⁻⁶ mbar).