Growth of High-Quality Pb(ZrxTi1-x)O3 Films by Peroxide MBE and Their Optical and Structural Characteristics
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0966-T11-17
Growth of High-Quality Pb(ZrxTi1-x)O3 Films by Peroxide MBE and Their Optical and Structural Characteristics Natalia Izyumskaya1, Vitaliy Avrutin1, Xing Gu1, Umit Ozgur1, Bo Xiao1, Tae Dong Kang2, Hosun Lee2, and Hadis Morkoc1 1 Department of Electrical and Computer Engineering, Virginia Commonwealth University, 601 West Main St., Richmond, VA, 23284 2 Deptartment of Physics, Kyung Hee University, Yong-In 446-701, Kyung Hee, Korea, Republic of ABSTRACT The growth of Pb(ZrxTi1-x)O3 (PZT) films by molecular beam epitaxy was demonstrated. Single-crystal, single-phase PZT films were grown on (001) SrTiO3 substrates at a growth temperature of 600∞C. In situ monitoring of the growth process by reflection high-energy electron diffraction revealed two dimensional growth for the PZT constituent ternaries, namely, PbTiO3 and PbZrO3, and three-dimensional growth for PZT films of intermediate compositions. Layer-by-layer growth of PZT films, however, was achieved by using a PbTiO3 buffer layer between the SrTiO3 substrate and PZT films. Optical properties of the films of the end ternaries were investigated by spectroscopic ellipsometry. Refractive index at 633 nm was found to be 2.66 for PbTiO3 and 2.40 for PbZrO3. Band gap energies of PbTiO3 and PbZrO3 were determined as 3.81 and 3.86 eV, in good agreement with theoretically calculated values. The P-E hysteresis loop of a 70nm-thick PZT film was well saturated and had a square shape. The remanent polarization and the coercive field were 83 µC/cm2 and 77 kV/cm, respectively, which are respectable. INTRODUCTION Due to their large piezoelectric coefficient, electrical polarization, and electromechanical coupling factor, ferroelectric Pb(ZrxTi1-x)O3 (or PZT) thin films are of considerable interest for a wide range of applications, such as gate material for ultrasonic sensors, motion sensors, infrared detectors, ferroelectric field effect transistors, and nonvolatile ferroelectric random access memory devices [1]. Piezoelectric and ferroelectric properties of this material prepared by a variety of techniques have been studied extensively as a function of composition. It was demonstrated that the piezoelectric coefficient, relative permittivity, and remanent polarization peaked near the morphotropic phase boundary [2]. To exploit the unique properties of PZT for device applications, high quality single-crystal PZT films are required. However, most of the studies have been performed on ceramic samples, whereas the properties of single-crystal thin films can differ drastically from those of ceramics [3] and depend strongly on film orientation [4-7]. PZT thin films have been prepared by various methods such as metal organic chemical vapor deposition (MOCVD) [4-6], rf magnetron sputtering [8-10], pulsed laser deposition [11,12], and sol-gel technique [13,14]. To the best of our knowledge,
molecular beam epitaxy (MBE), a modern growth technique providing high crystal perfection and precise control over material composition, has not been used for the PZT films up to now, al
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