MOCVD Growth of Two-Dimensional InSe Exhibiting High Electron Mobility

To keep pace with Moore's Law [1], transistors must shrink in size while maintaining exceptional performance. On the one hand, there is a fundamental limitation for 3D semiconductor-based transistor gates in miniaturization, as their size is limited to a few nanometers due to the rapid performance degradation, mainly due to increased surface scattering effects [2]. On the other hand, 2D materials have become a fascinating field of research since the preparation and investigation of graphene receiving the Noble Prize for Physics in 2010 [3]. In fact, some of these thin 2D materials are semiconductors with high field effect mobilities and could replace common 3D semiconductors as gate materials with improved miniaturization [2].<br/>However, the new transistor materials must not only have the right intrinsic properties, but their synthesis and processing must also be cost-effective, reliable, and scalable. To address these challenges, metal organic chemical vapor deposition (MOCVD) has been a growth method of choice.<br/>In particular, group III chalcogenides, such as indium selenide (InSe) [4] or gallium sulfide (GaS) [5], can be grown with metal-organic precursors established in the III-V laser industry, which decompose at low temperatures and are free of oxygen. In this study, we focus on layered InSe, which is known to exhibit high field effect mobility [6,7]. Its application for logic devices has been demonstrated [7]. However, a major challenge of InSe growth is its rich phase diagram, which leads to undesired phases of In_xSe_y [8,9].<br/>Sensitive adjustment of the supplied ratio of di-iso-propyl selenium (DiPSe) and tri-methyl indium (TMIn) allows us to grow single phase InSe homogeneously on 2" c-plane sapphire as verified by Raman spectroscopy. The number of layers grown depends on the growth time. We show by atomic force microscopy (AFM) that the growth starts from small nuclei that grow together to form a coalesced single layer film. After the first layer is closed, the growth behavior changes. This change is attributed to a different environment for precursor decomposition at the surface, underlining the importance of surface chemistry. The second layer contains InSe triangles up to 2 µm in size. In addition to AFM and Raman, we also use diffraction-based methods such as Scanning transmission electron microscopy (STEM) and in-plane X-ray diffraction (XRD) to develop a growth model.<br/>Terahertz time domain spectroscopy studies of MOCVD grown InSe indicate high carrier mobility in the range of 1000 cm2/(Vs) as expected from the literature [4,6].<br/>The talk will summarize our current understanding of 2D InSe growth and its properties and discuss some improvements, including the fabrication of heterostructures of InSe and other van der Waals materials.<br/><br/><b>References: </b><br/>[1] Moore, Gordon E., IEEE solid-state circuits society newsletter 11.3 (2006): 33-35. https://doi.org/10.1109/N-SSC.2006.4785860<br/>[2] Su, Sheng-Kai, et al., Small Structures 2.5 (2021): 2000103. https://doi.org/10.1002/sstr.202000103<br/>[3] Novoselov, Kostya S., et al., science 306.5696 (2004): 666-669. https://doi.org/10.1126/science.1102896<br/>[4] Song, Seunguk, et al., Matter 6.10 (2023): 3483-3498. https://doi.org/10.1016/j.matt.2023.07.012<br/>[5] Maßmeyer, Oliver, et al., Small (2024): 2402155. https://doi.org/10.1002/smll.202402155<br/>[6] Arora, Himani, and Artur Erbe, InfoMat 3.6 (2021): 662-693. https://doi.org/10.1002/inf2.12160<br/>[7] Feng, Wei, et al., Advanced materials 26.38 (2014): 6587-6593. https://doi.org/10.1002/adma.201402427<br/>[8] Zhang, Xiaotian, et al., Journal of Crystal Growth 533 (2020): 125471. https://doi.org/10.1016/j.jcrysgro.2019.125471<br/>[9] Okamoto, H. "In-Se (indium-selenium)." Journal of phase equilibria 19.4 (1998): 400-400. https://doi.org/10.1361/105497198770342175