Growth and characterization of c-axis oriented LiNbO 3 film on a transparent conducting Al:ZnO inter-layer on Si
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Monika Tomar and K. Sreenivas Department of Physics and Astrophysics, University of Delhi, Delhi-110007, India (Received 7 January 2004; accepted 3 March 2004)
C-axis oriented lithium niobate (LiNbO3) films were deposited by pulsed-laser deposition on silicon using a transparent conducting interlayer of aluminum (Al)-doped zinc oxide (ZnO). Only two x-ray diffraction reflections corresponding to (006) and (0012) planes of LiNbO3 were observed in the films deposited at a 100-mTorr oxygen pressure and a 450–500 °C substrate temperature. Presence of sharp modes corresponding to E(TO) and A(LO), and absence of any superfluous peaks mainly around 900–905 cm−1 in the Raman spectra confirmed the formation of textured LiNbO3 film. Measured value of direct current and alternate current (AC) conductivities and dielectric constant are 8.6 × 10−12 ⍀−1cm−1, 1.16 × 10−6 ⍀−1cm−1, and 29.3, respectively, at room temperature. Behavior of dielectric constant and AC conductivity with frequency and temperature are close to the reported single-crystal data.
I. INTRODUCTION
Applications for LiNbO3 thin films possessing good piezoelectric and electro-optic properties can be envisioned in a variety of integrated acousto-optic and electrooptic devices.1–6 LiNbO3 in thin-film form is an attractive choice over the bulk, because of the possibility to produce step-index profiles and dopant introduction. Additionally, high electric fields can be easily achieved at a lower voltage. It is desirable to grow LiNbO3 films with a preferred crystallographic orientation, having c-axis normal to the substrate to couple the large electro-optical and non-linear optical coefficients along this direction.4 The search for appropriate substrate materials and buffer layers that promote the desired crystallization of LiNbO3 thin films have attracted a lot of attention. Interfacing LiNbO3 films with electrode layers (that are preferably transparent and conducting) are of immense importance to probe its electro-optic properties. Wave-guiding on silicon is becoming equally important for fabricating integrated optical devices.1–6 Many reports are available on the successful growth of c-axis oriented LiNbO3 films on lattice-matched, single-crystal substrates.6,7 However, significant problems are encountered when attempts are
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2004.0322 J. Mater. Res., Vol. 19, No. 8, Aug 2004
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made to deposit LiNbO3 films on Si using various buffer layers (e.g., SiO2, Si3N4, Al2O34,8,9). Such attempts demand careful optimization of the deposition conditions. Mostly the films are either amorphous, or possess a mixed orientation with undesirable phases, LiNb3O8 or Li3NbO4 due to stoichiometric inhomogeneity. Little success has been achieved with the growth of c-axis oriented LiNbO3 films.8–10 However, their reproducibility is poor under identical growth conditions.8 Ultra-thin buffer layers of ZnO have been shown to be effective
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