Self-catalyzed InP Nanowires on Patterned Si Substrates
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Self-catalyzed InP Nanowires on Patterned Si Substrates Kenichi Kawaguchi1, Hisao Sudo2, Manabu Matsuda2, Kazuya Takemoto2, Tsuyoshi Yamamoto2, and Yasuhiko Arakawa1,3 1 NanoQuine, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan. 2 Fujitsu Laboratories Ltd., 10-1 Morinosato-Wakamiya, Atsugi, 243-0197 Japan. 3 IIS, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo 153-8505, Japan. ABSTRACT Self-catalyzed growth of position-defined InP nanowires (NWs) was investigated on SiO2-mask-pattered Si substrates using metalorganic vapor-phase epitaxy. Using low growth temperatures and high group-III flow rates, pyramidal InP NWs were formed vertically on the mask openings. The diameter and tapering of the InP NWs were successfully controlled by the introduction of HCl and H2S gases during the NW growth. In addition, crystal growth of radial InP/InAsP/InP quantum wells on the sidewall of the InP NWs was performed on Si substrates. INTRODUCTION InP-related NWs are attractive as a base structure for near-infrared optical devices [1][3]. InP NWs are formed by using bottom-up growth methods such as vapor-liquid-solid (VLS) method or selective-area growth method. The VLS growth method using metal catalytic particles allows us to grow NWs with low process temperatures. The selective-area growth using SiO2 masks is suitable for controlling the position of NWs. As a technique combining both methods, VLS growth of position-controlled InP NWs using a SiO2-mask patterned InP substrate with Au catalysts has been reported [4], [5]. Using HCl gas introduction during the NW growth as a controlling method of the NW shape, position-defined InP NWs aligned as 2-D array were demonstrated using low growth temperature of around 400°C [5]. The crystal phase of such arrayed VLS-InP NWs can be controlled to wurtzite (WZ) crystal phase, using S-doping by H2S [5]. Moreover, it was reported that this position-defined InP NW array on patterned InP substrates can be used as a template for forming optically-active heterostructure NWs [6] and light-emitting NW devices [7]. Thus, fabrication technique of InP-related NW for optical device application has been favorably developed on InP substrates. From the practical point of view, the successful implementation of such VLS InP NWs onto Si substrates is important, since it will pave the way to the realization of monolithic integration with other Si-based devices such as silicon photonics and/or CMOS. For the NW growth, however, changing substrates is expected to cause some differences. The most crucial thing is the selection of metal catalysts. Although Au is one of the best metal catalysts for the VLS growth of InP NWs, Au forms deep-level centers when it is incorporated into Si. Therefore, Au should not be used for the NW catalyst if we integrate monolithically the NW devices with other devices on Si substrates in the future. As a way of VLS-InP NW growth without Au catalysts, self-catalyzed VLS growth mode originated from In particles has been reported on bare Si substrates [8],
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