Abstract

Rare-earth doping of thin films has been gaining increasing attention for optically active waveguide devices. Er-doped BaTiO₃ is of particular interest due to the possibility of combining excellent electrooptical and nonlinear optical proper ties of BaTiO₃ and the characteristic luminescence properties of Er ions. We report on structural, electrical, and photoluminescence properties of Er-doped BaTiO₃ films deposited by rf magnetron sputtering. The Er-doped films (0.5-0.7 μm thick) were deposited on MgO (001) single-crystal substrates at various temperatures (500-800 °C). Er was doped into BaTiO₃ by co-sputtering a BaTiO₃ target and an elemental Er target in reactive ambient (Ar/O₂). Er concentration was in the range of 10¹⁹-10²⁰ atoms/cm³. Deposition rate was measured to be 70 A/min. Deposited films were examined by 0/20 X-ray diffraction. (See Fig. 1). The film deposited at 500 °C is weakly oriented with a mixture of the (111)- and (001)- BaTiO₃ peaks. (The peaks at 43°, 41°, and 38.5° are MgO (002) reflections with CuKα, CuKβ, and tungsten Lβl radiations, respectively.) As the deposition temperature was increased to 600 °C, the (001)-plane peak became well-defined and also stronger than the (111) peak. At 700 °C, the film became highly (001) oriented and the (111) peak disappeared completely. The film shows only (00l)-plane peaks of BaTiO₃ in the 2θ scan range of 20-50°. As the deposition temperature was further increased to 800 °C, both the (001)- and (002)-plane peaks increased significantly. Although the (101)-BaTiO₃ peak appears at 2θ = 31°, the intensity of the peak is of a trace level, i.e., three orders of magnitude lower than that of the (002)-plane peak. Fig. 2 shows a pole figure of the film deposited at 700 °C for (202) reflections which are 45° off normal to the surface. The four fold symmetry indicates that the film has an epitaxial relationship with the MgO surface. The X-ray diffraction ϕ scan confirms the in-plane epitaxial relationship of BaTiO₃[100] ‖ MgO[100], The film deposited at 800 °C also shows the same pole figure and in-plane epitaxial relationship. This indicates that the presence of the small amount of the (101) crystallites does not affect the epitaxial relationship of the film with the MgO surface. Fig. 3 shows a room-temperature photoluminescence spectrum of the Er-doped BaTiO₃ film deposited at 800 °C. The 488 nm line of an Ar⁺ laser was used for optical pumping of Er ions. The spectrum is peaked at 1.546 μm and a side peak is observed at 1.556 μm. The wavelength region around 1.55 μm corresponds to the internal 4f transitions (⁴I_13/2 → ⁴I_15/2) of Er³⁺ ions. Fluorescence decay lifetime measurement is being carried out, and details of the measurement result will be reported. Guided-wave optic properties, such as propagation loss and refractive index, will also be reported.

© 1995 IEEE