Towards large-scale, high crystalline quality and defect controlled van der Waals semiconductors

Place: Conference room, IMDEA Nanociencia.

Abstract: 

Two-dimensional (2D) crystals “beyond graphene” have sparked immense interest in recent years, due to their excellent tunability, efficient light-matter coupling and miniaturization capabilities [1]. However, urgent efforts are necessary for the understanding of the impact on their functionalities of mid-gap defects. Layered van der Waals (vdW) crystals are realized by stacking 2D materials with thicknesses between monolayer and bulk, and their high-quality and large-scale epitaxial growth remains an unexplored field that can be exploited for the development of novel semiconductor device technologies. Here, we discuss recent research that addresses these challenges by combining exfoliation or molecular beam epitaxy (MBE) with advanced microscopic, spectroscopic and electrical characterizations supported by density functional theory calculations. We focus on 2D gallium monochalcogenides (group III-VI), an emerging class of layered semiconductors with low in-plane symmetry that gained traction in “more-than-Moore”, next generation optoelectronic and renewable energy device applications but shows high reactivity in ambient conditions [2, 3]. In order to study the pristine information of air sensitive materials, we present a cutting edge UHV cluster tool for the synthesis of vdW crystals and their heterostructures. The system consists of an MBE connected via automated UHV transfer channel to an analytical chamber with in-situ optical confocal spectroscopy (photoluminescence and Raman) at lattice temperatures 300 K to ~10 K. Our results highlight fabrication methods for single crystal 2D anisotropic semiconductors and explores ways to control unstable phases of matter, both highly relevant for the realization of 2D layered films based multifunctional devices.

 [1] A. K. Geim, and I. V. Grigorieva, Nature 499 (2013) 419.

[2] Cai, et al., Appl. Phys. Rev. 6 (2019) 041312.

[3] E. Zallo, et al., npj 2D Mater Appl 7 (2023) 19.