Applied Materials Today 20 (2020) 100734 Contents lists available at ScienceDirect Applied Materials Today journal homepage: www.elsevier.com/locate/apmt Epitaxial growth of In 2 Se 3 on monolayer transition metal dichalcogenide single crystals for high performance photodetectors Pranab K Mohapatra a , Kamalakannan Ranganathan a,† , Lital Dezanashvili a,† , Lothar Houben b , Ariel Ismach a,∗ a Department of Materials Science and Engineering, Tel Aviv University, Ramat Aviv, Tel Aviv, 6997801, Israel b Chemical Research Support, Weizmann Institute of Science, Rehovot 76100, Israel a r t i c l e i n f o Article history: Received 16 April 2020 Revised 9 June 2020 Accepted 17 June 2020 Available online xxx a b s t r a c t One of the most intriguing properties of layered materials is their ability to form inherently ultra-thin atomically sharp vertical interfaces and hybrid layered compounds, in moderate environment conditions, which are ideal platforms for both, scientific research and many applications. Here, we present the se- lective van der Waals epitaxial formation of β -In 2 Se 3 on transition metal dichalcogenides (TMDCs). This is achieved in a two-step chemical vapor deposition (CVD) process, in which first, the monolayer TMDC, is synthesized and then the β -In 2 Se 3 is grown on top of it. The thickness of the second phase can be controlled by the growth conditions, while the crystal size is dictated by the MoS 2 single-crystal do- main size. High-resolution transmission electron microscope (HRTEM) studies reveal a clean and sharp interface, while selected area diffraction (SAED) demonstrates a clear registry between both phases. The hybrid layered-compound exhibit better electrical transport than the intrinsic indium-selenide layer. The high crystallinity of In 2 Se 3 grown on MoS 2 yield fast response among the CVD-derived In 2 Se 3 -based pho- todetectors with rise/fall times of 4/7 ms, photoresponsivity of up to ~23 A/W and specific detectivity of ~5 × 10 11 . Our methodology allows high quality thin In 2 Se 3 layers to be formed via van der Waals epitaxy on TMDCs, forming complex vertical heterostructures for optoelectronic applications. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction Research in 2D materials has been intense in the last decade due to the unique scientific and technological opportunities such materials offer [1–5]. Among these, the possibility to achieve epi- taxial growth, even when the mismatch between the 2D epilayer and the substrate is large, as was pioneered by Koma and co- workers [6], when coined the term “van der Waals (vdW) epitaxy” to describe the oriented growth of layered materials (on other 2D materials or 3D crystals). This is possible due to the unique bond anisotropy in layered compounds that enables large strain relax- ation. However, these studies were done in ultra-high vacuum con- ditions, which may have inhibited further research and its imple- mentation for the assembly of functional devices. Great achievements were made in the last years on the synthe- sis of intrinsic 2D materials, in which, chemical vapor deposition (CVD) [2,5,7–11] and metal-organic CVD (MOCVD) [12–14] are con- sidered the leading methodologies to achieve large-scale growth of ∗ Corresponding author. E-mail address: aismach@tauex.tau.ac.il (A. Ismach). † These authors contributed equally to this work high quality ultra-thin films. Despite the great advance, the ratio- nal growth of atomic-layers over large areas still represent a signif- icant challenge in the field. One of the most important parameters in materials in general is their grain size, as it usually has signif- icant impact on its physical and chemical properties. The domain size in 2D material films is of similar relevance and often, hard to control. Epitaxial growth has the advantage of leading to high- quality thin films without the need to achieve a severe control over the nucleation density, since all the domains are equally oriented. Therefore, finding a suitable substrate for the vdW epitaxial growth is of high importance. The success in growing 2D materials via CVD and MOCVD methodologies, sparked new studies based on such methodologies to grow 2D hybrid layered compounds via vdW epi- taxy. The vast majority of this research was concentrated on the TMDC family, graphene and h-BN [15–19]. However, many other layered compounds offer very rich physical and chemical proper- ties as well, such as the In-, Ga- and Sn- chalcogenides [20] and the indium selenide phases in particular [21–25]. Less research has been done on the growth as well the rational formation of hybrid- layered structures of this type of materials [14,25–29]. β -In 2 Se 3 is an interesting member of the group IIIA−VIA lay- ered material and is typically n-type semiconductor with a rel- https://doi.org/10.1016/j.apmt.2020.100734 2352-9407/© 2020 Elsevier Ltd. All rights reserved.