Characteristics of Ge-AlN core-shell microneedles Kyoung Hwa Kim 1 , Suhyun Mun 1 , Seonwoo Park 1 , JeongBin Heo 1 , MinGyeong Jo 1 , Jae Hak Lee 1, 2 , Hyung Soo Ahn 1, * Min Yang 1 , Young Tea Chun 1 , Won Jae Lee 3 , Sang-Mo Koo 4, * 1 Department of Nano Semiconductor, Korea Maritime and Ocean University, Busan 49112, South Korea. 2 LNBS Co., Ltd. Busan 48731, South Korea. 3 Department of Advanced Materials Engineering, Dong-Eui University, Busan 47340, South Korea. 4 Department of Electronic Materials Engineering, Kwangwoon University, Seoul 01897, South Korea. E-mail: kimkh@kmou.ac.kr The core-shell structure in semiconductors is crucial for device applications, as it allows for the formation of stacked nanostructures and nano-composites that induce changes in material properties. Therefore, the development of core-shell bonding techniques using arbitrary materials is highly important [1]. In this study, we propose a new mechanism for the formation of Ge-AlN core-shell microneedles by AlN nanowires using the mixed-source HVPE method. A Ge-AlN core-shell microneedles with a droplet size of approximately 100μm was formed on a hexagonal microneedles with a length of 400 μm and a maximum width of 55 μm. FE-SEM images confirmed that Ge droplets were formed on the surface of the initial AlN nanowires, and the droplets played a role as a source for forming Ge-AlN core-shell microneedles. EDS measurement showed that both the droplet and the microneedle contained Ge, Al, and N components. Cross-sectional EDS mapping showed that the shell was composed of 95.62 at.% Al, while the core was composed of 98.15 at.% Ge. We found that the formation of the Ge-AlN core-shell microneedle was different from the typical core-shell formation, as the core was filled after the shell was formed. The core grew along the length direction due to the absorption of Ge atoms inside the shell, and gradually expanded in the lateral direction to fill the shell. The Raman spectrum of the Ge-AlN core- shell microneedle showed an E 2g mode at 293.7 cm -1 , which is not observed in cubic Ge. The E 2g mode shift was 2.4 cm -1 along the full length of the microneedle, indicating the stable growth of a bulk -like Ge-AlN core-shell microneedle. Therefore, we propose that the Ge-AlN core-shell structure, which is not in the nano-size regime, could provide a new possibilities for next-generation high-speed electronic and optoelectronic devices. Acknowledgment This research was supported by the Korea Evaluation Institute of Industrial Technology (KEIT) grant funded by the Korea government (MOTIE) (RS-2022-00154720, Technology Innovation Program Development of next-generation power semiconductor based on Si-on-SiC structure). References 1. Lauhon, L. J., Gudiksen, M. S., Wang, D., &Lieber, C. M. Epitaxial core-shell and core-multishell nanowire heterostructures. Nature 420, 57−61 (2002).
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