Rapidly resolving bilayer stacking orientation in industrially compatible MOCVD-grown MoS₂ films through second harmonic generation imaging

Abstract

Atomically thin semiconductor films grown by metal organic chemical vapor deposition (MOCVD) will be crucial for the integration of two-dimensional (2D) materials into semiconductor devices produced at scale. However, the development of wafer-scale growth techniques has outpaced the development of corresponding metrology to assess film quality of 2D transition metal dichalcogenide (TMD) films. One particularly difficult issue is that the stacking sequence when overgrowing TMD films is not uniquely defined, with different possible orientations for the second layer. Determining this stacking order of individual grains when growing additional layers over a closed monolayer is an outstanding challenge for such films. Here, we use second harmonic generation (SHG) microscopy to assess the size, dispersion, and stacking orientation of bilayer grains in MOCVD-grown MoS2 films. We correlate several microscopy techniques—bright-field white-light microscopy imaging, atomic force microscopy, photoluminescence mapping, and SHG microscopy—to show that SHG can uniquely map the stacking orientation of bilayer nucleates in these films. We expect this to drive the development of further metrology based on SHG for semiconductor applications, especially in the development of 2D material specific tools.