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MBE growth and properties of ZnO on sapphire and SiC substrates
Authors:M A L Johnson  Shizuo Fujita  W H Rowland  W C Hughes  J W Cook  J F Schetzina
Affiliation:(1) Department of Physics, North Carolina State University, 27695-8202 Raleigh, NC;(2) Present address: Department of Electronic Science and Engineering, Kyoto University, 606-01 Kyoto, Japan
Abstract:Molecular beam epitaxy (MBE) of ZnO on both sapphire and SiC substrates has been demonstrated. ZnO was used as a buffer layer for the epitaxial growth of GaN. ZnO is a würtzite crystal with a close lattice match (<2% mismatch) to GaN, an energy gap of 3.3 eV at room temperature, a low predicted conduction band offset to both GaN and SiC, and high electron conductivity. ZnO is relatively soft compared to the nitride semiconductors and is expected to act as a compliant buffer layer. Inductively coupled radio frequency plasma sources were used to generate active beams of nitrogen and oxygen for MBE growth. Characterization of the oxygen plasma by optical emission spectroscopy clearly indicated significant dissociation of O2 into atomic oxygen. Reflected high energy electron diffraction (RHEED) of the ZnO growth surface showed a two-dimensional growth. ZnO layers had n-type carrier concentration of 9 × 1018 cm−3 with an electron mobility of 260 cm2/V-s. Initial I-V measurements displayed ohmic behavior across the SiC/ZnO and the ZnO/GaN heterointerfaces. RHEED of GaN growth by MBE on the ZnO buffer layers also exhibited a two-dimensional growth. We have demonstrated the viability of using ZnO as a buffer layer for the MBE growth of GaN.
Keywords:GaN  molecular beam epitaxy (MBE)  oxygen plasma  reflected high energy electron diffraction  ZnO
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