Highly textured Pb(Zr 0.3 Ti 0.7 )O 3 thin films on GaN/sapphire by metalorganic chemical vapor deposition
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Highly (111) textured Pb(Zr0.3Ti0.7)O3 (PZT 30/70) films were deposited on (0001) GaN/sapphire substrates using liquid-source metalorganic chemical vapor deposition (MOCVD) technique at 520 °C and 80 nm/min. The crystallinity of as-deposited PZT films and the structure of PZT/GaN interface were evaluated by x-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM), respectively. Mitigated by geometric epitaxy and strain energy minimization, the orientation relationships of PZT on epi-GaN, determined using x-ray pole figure and selected area diffraction pattern, were as follows: out-of-plane alignment of [111] PZT//[0001] GaN, and orthogonal in-plane alignments of [112¯] PZT//[11¯00] GaN (zone axes) and [11¯0] PZT//[112¯0] GaN. The nanochemistry of the PZT (150nm)/GaN interface, studied using analytical TEM, indicated a chemically sharp interface with interdiffusion limited to a region below 5 nm. The properties of as-deposited PZT on GaN by MOCVD are briefly compared with PZT by sol-gel processing, radio-frequency sputtering, and pulsed laser deposition.
I. INTRODUCTION
Lead zirconate titanate [Pb(ZrxTi1−x)O3; or PZT] is a multifunctional oxide system that possesses dielectric, pyroelectric, piezoelectric, electro-optic, and ferroelectric properties.1–5 In the past couple of decades, the impetus for research on Si-integrated PZT films has primarily been on the development of nonvolatile ferroelectric random access memories (FeRAMs),6–10 piezoelectricbased microelectromechanical systems,11–14 and pyroelectric infrared (IR) detectors.15–17 An early report on the deposition of epitaxial (Pb, La)(Zr, Ti)O3 (PLZT) thin films on GaAs and GaP substrates for electro-optics and nonlinear optics18 was followed by the deposition of PZT films on GaAs for FeRAMs.19,20 Recently, the integration of PZT on cubic and wurtzite GaN for potential applications in microwave power and optoelectronic devices, as well as metal-ferroelectric-semiconductor field effect transistor (MFSFET) devices, has been demonstrated.18,21–26 Moreover, due to multiple advantages of wide band gap GaN as a resonator material, the ferroelectric PZT/semiconductor GaN heterostructure is being explored in radio-frequency (rf) microelectromechanical systems (MEMS) devices for insertion in rf communication systems.26–29
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Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/JMR.2006.0184 1526
http://journals.cambridge.org
J. Mater. Res., Vol. 21, No. 6, Jun 2006 Downloaded: 16 Mar 2015
To date, a variety of processing techniques including rf sputtering, pulsed laser deposition (PLD), and sol-gel have been successfully used to deposit PZT films on group III nitride semiconductors.18,23,25–29 However, for commercial-scale production of device-quality PZT thin films on GaN, a manufacturable metalorganic chemical vapor deposition (MOCVD) process must be developed, a technique that offers a number of advantages, including excellent film uniformity on large substrates, good compositional control, high dep
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