Control of Crystal Orientation of Epitaxial Si nanowires on Si Substrate Using AAO template
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Control of Crystal Orientation of Epitaxial Si nanowires on Si Substrate Using AAO template Tomohiro Shimizu1, Qi Wang1, Chonge Wang1, Fumihiro Inoue1, Makoto Koto2, Minsung Jeon1 and Shoso Shingubara1 1 2
Faculty of System Engineering Science, Kansai University, Suita, Osaka 564-8680, JAPAN Corporate R&D headquarters, Canon inc., Ohta, Tokyo 146-8501, JAPAN
ABSTRACT Control of crystal orientation of vertically grown epitaxial Si (111) and (110) nanowire arrays on Si substrate has been demonstrated using a combination of an anodic aluminum oxide (AAO) template and vapor – liquid – solid (VLS) growth method. The crystal orientation of the nanowire was investigated by transmission electron microscopy. A growth direction of the nanowire arrays was guided perpendicular to the surface of the substrate by the AAO template, and the crystal orientation of the nanowire arrays was selected using the single crystal Si substrate properly cut in desired orientation.
INTRODUCTION Epitaxial Si nanowires grown without any template on Si substrates reported up to now have three preferred growth directions, in particular , , and depending on the diameter of the wires [1]. Based on the present knowledge the preferred growth directions of the epitaxial Si nanowire are for larger diameter than 20 nm and and for smaller diameters, if no template is used. In our previous study, growth of vertical epitaxial Si (100) nanowires on Si (100) substrates, which was not grown naturally, was realized using a combination of the anodic aluminum oxide (AAO) template, catalytic gold (Au) particles embedded in nanopores directly on the Si substrate by electroless deposition and Vapor-LiquidSolid (VLS) growth [2]. In this paper, we demonstrated control of crystal orientation of epitaxial nanowire independently from the diameter size using previous template growth method and choosing crystal orientation of Si substrate. EXPERIMENT Figure 1 shows schematic drawing of the sample preparation. At first, Al films were deposited by sputtering on H-terminated Si (111) and (110) substrates respectively for preparation of AAO/Si structure as anode. Electrical contact of the back side was made by pressing the Si substrate to a copper (Cu) block. The temperature of the Cu block was maintained at 5 oC. The Al films were anodized in an electrolyte based on oxalic acid (0.3 M H2C2O4 with deionized water) at 40 V with a two step anodization technique [3]. The first anodization was
stopped when the thickness of the rest of the Al film on the Si substrate reached about 500 nm. After selective etching of the first AAO film by wet chemical etching (30 min, 60 oC, mixture of 6 wt% phosphoric acid and 1.8 wt% chromic acid) a second anodization was performed until the whole Al film changed into AAO. Then, we slightly etched the aluminum oxide by diluted phosphoric acid (20 min, 30 oC, 5%). At this point, although the Si surface at each nanopore bottom was still covered by a Si oxide film, we obtained an AAO template, whose diameter of nanopores was wider at the bottom th
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