Photoconductive Bi 12 MO 20 -type films prepared by pulsed laser deposition
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Photoconductive Bi12MO20-type films prepared by pulsed laser deposition J.E. Alfonso,a) M.J. Martín, V. Volkov,b) and C. Zaldoc) Instituto de Ciencia de Materiales de Madrid, Consejo Superior de Investigaciones Cientı´ficas, Cantoblanco, 28049 Madrid, Spain
M. Aguilo´ Laboratori de Fı´sica Aplicada i Cristal.lografia, Universitat Rovira I Virgili, 43005 Tarragona, Spain
M.F. da Silva Instituto Tecnolo´gico e Nuclear, Departa´mento de Fı´sica, Estrada Nacional n 10, 2685 Sacave´m, Portugal
J.C. Soares Centro de Fı´sica Nuclear da Universidade de Lisboa, Av. Prof. Gama Pinto 2, 1699 Lisboa, Portugal (Received 28 January 1998; accepted 2 August 1999)
Bi12TiO20 (BTO); Bi12GaxBi1−xO19.5 (BGaO); and Bi12(M1/3P2/3)O20, M ⳱ Cd, Zn, and Ni (BMPO) thin films were prepared by pulsed laser deposition using a KrF excimer laser on (100)Y-stabilized zirconia (YSZ), (100)Bi12GeO20 (BGO), and (110)Bi12SiO20 (BSO) crystalline substrates. All these films have a sillenite structure. On (100)YSZ the sillenite is oriented as {310} with the 〈130〉 direction parallel to the 〈021〉YSZ directions (〈130〉{310}BTO㛳〈021〉{100}YSZ). On (100)BGO and (110)BSO the sillenite film reproduces the substrate orientation, and the films formed are able to channel He+ particles. The optimum deposition temperatures for BTO and BGaO are 600 and 550 °C, respectively. Higher temperatures must be avoided to minimize the nucleation of Bi-deficient phases due to the diffusion of Bi into the YSZ substrates. BMPO films are polycrystalline. The lattice parameters of these films were determined. The crystalline films support guided optical modes. The refractive indices obtained for the films are close to those measured in bulk crystals, being slightly larger for films deposited on isomorphous sillenite substrates. The crystalline films deposited on YSZ are photoconductors when excited in the green and blue spectral regions.
I. INTRODUCTION
The integration of nonlinear optical media with solidstate lasers is still a challenging and incomplete task, which may yield miniaturized devices. Epitaxially grown films with a low defect concentration and good flatness are required to minimize optical losses and retain a high figure of merit in comparison with the nonlinear optical properties observed in bulk crystal. The photorefractive effect1 is a nonlinear optical effect based on the creation of a refractive index grating. This grating arises from the photoconductive and electro-
a)
Permanent address: Centro Internacional de Fı´sica, Santa Fe´ de Bogota´, Apartado Ae´reo 49490, Colombia. b) Permanent address: Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Lenisky Pr. 31, GSP-1, 117907 Moscow, Russia. c) Address all correspondence to this author. e-mail: [email protected] J. Mater. Res., Vol. 14, No. 11, Nov 1999
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optic properties of the medium. Bulk inorganic single crystals—namely, LiNbO3, KNbO3, SrBaNb2O6, BaTiO3, and the family
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