Effect of Growth Conditions on Structural and Electrical Properties of Pb(Zr x Ti 1-x )O 3 layers grown by peroxide MBE
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Effect of Growth Conditions on Structural and Electrical Properties of Pb(ZrxTi1-x)O3 layers grown by peroxide MBE N. Izyumskaya1, V. Avrutin1, X. Gu1, B. Xiao1, S. Chevtchenko1, Lin Zhou2, David J. Smith2, J.-G. Yoon1,3, and H. Morkoc1 1 Department of Electrical and Computer Engineering, Virginia Commonwealth University, Richmond, VA, 23284 2 Deptartment of Physics, Arizona State University, Tempe, AZ, 85287 3 Department of Physics, University of Suwon, Kyounggi-do, 445-743, Korea, Republic of ABSTRACT Pb(ZrxTi1-x)O3 (PZT) films were grown by molecular beam epitaxy using hydrogen peroxide as a source of reactive oxygen. Phase composition as well as structural and electrical properties of the films were studied by x-ray diffractometry, scanning and transmission electron microscopy, conductive atomic force microscopy, and electrical (IV and polarization-field) measurements. The hydrogen peroxide pressure was found to control the phase composition of the films. Excess peroxide leads to PbO inclusions in PZT layers, whereas deficiency results in the TiO2 or the ZrO2 phase. The second-phase inclusions can be responsible for high leakage current in the films. Precise control over the peroxide pressure is imperative for single-phase PZT films with good ferroelectric properties.
INTRODUCTION Ferroelectric Pb(ZrxTi1-x)O3 (PZT) films have attracted considerable interest owing to their potential applications in nonvolatile random access memory devices, ferroelectric field effect transistors, motion sensors, infrared detectors, surface acoustic wave devices, microactuators, as well as a plethora of applications in non linear optics. Harnessing PZT properties, however, requires high quality single-crystal PZT films. PZT thin films have been prepared by various methods such as sol-gel [1] and hydrothermal techniques [2], metal-organic chemical vapor deposition [3], rf magnetron sputtering [4], and pulsed laser deposition [5]. Recently, we reported epitaxial growth of high-quality PbTiO3 and PZT layers by molecular beam epitaxy (MBE) [6-9]. Here, we focus on the effect of growth conditions on structural and electrical properties of PZT films grown on (001) SrTiO3 substrates by MBE, with the use of hydrogen peroxide as an oxidant. EXPERIMENTAL DETAILS The PZT layers were grown in a modified Riber 3200 MBE system with the use of 50% aqueous solution of hydrogen peroxide (H2O2) as an oxidizer. Lead (99.999% pure) and titanium (99.995% pure) were supplied from double-zone and high-temperature
effusion cells, respectively. Because of the very low equilibrium pressure of metallic Zr, a metal-organic source was used. Zirconium tetra butoxide was chosen as the precursor, and 6N-purity Ar was used as the carrier gas. The films were grown on (001) undoped and Nb-doped SrTiO3 substrates. Before loading into the chamber, the substrates were etched in a buffered NH4F-HF solution, rinsed in deionized water and dried with nitrogen. In the growth chamber the substrates were thermally cleaned at 600 °C for 20 min under an H2O2/H2O
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