Out-of-Plane and In-Plane Crystalline Orientations of Oxide Heterostructures of LSMO/ZnO
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Out-of-Plane and In-Plane Crystalline Orientations of Oxide Heterostructures of LSMO/ZnO Kenichi Uehara1, Sanapa Lakshmi Reddy2, Akira Okada1, Miyoshi Yokura1, 3, Shintaro Kobayashi4, Katsuhiko Inaba4, Tomohiko Nakajima5, Tetsuo Tsuchiya5, Kazuhiro Endo6, Tamio Endo1 1
Mie University, 1577 Kurima, Tsu, Mie 514-8507, Japan. Department of Physics, S.V.D. College, Kadapa, India. 3 Adwel R&D Co., Ltd., Ritto City, Shiga, Japan. 4 Rigaku Corp. XRL, Bunkyo-ku, Tokyo, Japan. 5 Nat. Inst. AIST, Tsukuba, Ibaraki, Japan. 6 Kanazawa Inst. Tech., Nonoichi, Ishikawa, Japan.
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ABSTRACT Hexagonal ZnO was grown on hexagonal (001) sapphire substrate, then cubic La(Sr)MnO3 (LSMO) was grown on ZnO underlayer by ion beam sputtering at substrate temperatures of 550-750°C to obtain double-layer of LSMO/ZnO. Out-of-plane (001) oriented ZnO was grown with in-plane orientation of [10-10](0001)ZnO//[11-20](0001)sapphire. Mixed phase of LSMO with out-of-plane (001), (110) and (111) orientations was grown on (001) ZnO usually. However each single phase of LSMO could be grown by controlling deposition conditions. The LSMO grains have their in-plane orientations of [110](110)LSMO //[1010](0001)ZnO and [110](111)LSMO//[11-20](0001)ZnO. INTRODUCTION Perovskite manganite La(Sr)MnO3 (LSMO) reveals versatile electrical and magnetic properties such as colossal magnetoresistance [1], and is a p-type semiconductor at higher temperatures. ZnO is a n-type widegap (3.4 eV) semiconductor which is transparent for visible light but absorbs UV light. We are trying to obtain a novel p-n heterojunction of LSMO/ZnO system which must show unique p-n characteristics modified by magnetic field, temperature and UV light. Actually the modulations of junction characteristics by light illumination and temperature change were reported on LSMO/ZnO formed by PLD [2]. It was reported that a p-n junction of ZnO nanosheet on LSMO thin film shows an excellent rectification factor (ratio of forward to reverse current) of 120 [3]. It may be easier to fabricate p-n junction using the same cubic crystalline system such as LSMO/SrTiO3. However, it is not known whether this has superior rectification or not. Further, this p-n junction may not have stronger response to the UV light compared with LSMO/ZnO, because ZnO has strong UV light absorption around 3.4 eV. A conductivity of ZnO can be widely controlled by oxygen content and doping. This is also a reason why we employ ZnO for the heterojunction. On the other hand, it is more difficult but necessary to control the crystalline orientations of these materials of LSMO/ZnO to obtain superior and controllable junction characteristics. We fabricated double-layer thin films of LSMO/ZnO/sapphire-substrate by ion beam sputtering, and the single phases of out-of-plane (001), (110) and (111) LSMO with cubic system could be obtained on (001) ZnO with hexagonal system by controlling deposition conditions. Possible inplane orientation configurations of this system are drawn in Figure 1 with values of lattice
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constants, where non-funda
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