Exotic Doping for ZnO Thin Films: Possibility of Monolithic Optical Integrated Circuit
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ABSTRACT We propose the application of ZnO:X (X = Li, Mg, N, In, Al, Mn, Gd, Yb etc.) films for a monolithic Optical Integrated Circuit (OIC). Since ZnO exhibits excellent piezoelectric effect and has also electro-optic and nonlinear optic effects and the thin films are easily obtained, it has been studied as one of the important thin film wave guide materials especially for an acoustooptic device[1 ]. In terms of electro-optic and nonlinear optic effects, however, LiNbO, or LiTaO, is superior to ZnO. The most important issue of thin film waveguide using such ferroelectrics is optical losses at the film/substrate interface and the film surface, because the process window to control the surface morphology is very narrow due to their high deposition temperature. Since ZnO can be grown at extremely low temperature, the roughness at the surface and the interface is expected to be minimized. This is the absolute requirement especially for waveguide using a blue or ultraviolet laser. Recently, lasing at the wavelength of ultraviolet, ferroelectric and antiferromagnetic behaviors of ZnO doped with various exotic elements (exotic doping) have
been reported. This paper discusses the OIC application of ZnO thin films doped with exotic elements.
INTRODUCTION The optical Integrated Circuit (OIC) is one of the promising device which can control large amounts of information. A compact, blue laser source is of great interest as applied to optical data storage. Ferroelectric thin films offer several advantages over bulk materials for optical waveguides, though no device superior to bulk devices exists yet. One advantage is the larger refractive index difference between the ferroelectric layer and the cladding, which are dissimilar materials, such as LiNbO, and sapphire. Thin films, therefore, permit higher intensity per unit power in the guide, and hence larger non-linear effects, and shorter interaction lengths[2]. Although the OIC using thin films has been investigated for over 30 years, none of
317 Mat. Res. Soc. Symp. Proc. Vol. 574 ©1999 Materials Research Society
them have demonstrated reliably low loss waveguides with bulk-like electro, magneto or acousto-optic effects. Such materials should have anisotropy in crystal structure and have usually complicated structure with multiple components. For example, ferroelectric Pb, La(ZrxTi,-x)O, (PLZT) has excellent electro-optic effect (Kerr effect) and various studies on the application of optical switching have been carried out [3,4]. In this complex oxide including a volatile element, however, several issues such as surface roughness and reproducibility exist. Although the problems are improving [5], high formation temperature might be a fatal problem. On the other hand, Zinc Oxide with simple structure has variety of physical properties such as n-type semiconductor, varistor, transparent conductive film, piezoelectric effect, electro-
optic effect (Pockels effect), and acousto-optic effect. Although this material has strong crystallographic anis
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