Stability of Structural and Optical Properties of the Two-Dimensional WSe2 Monolayer at the Formation of a Spintronic Heterostructure for THz Emitters

Two-dimensional semiconductor transition-metal dichalcogenides (TMDs) are now considered promising active components of spintronic terahertz emitters due to their strong spin-orbit coupling and a unique ability to effectively filter spin-polarized electrons. However, electronic and optical properties of two-dimensional materials appreciably depend on the type of substrate used and the features of the technological process for producing spintronic THz heterostructures, which directly affects the functional characteristics of devices. In this work, a comprehensive investigation is performed to study the effect of the sapphire substrate and standard deposition stages on monolayer WSe2 as part of the Al2O3/2D–WSe2/Co terahertz emitter. The structural quality, optical characteristics, and the presence of mechanical strain in the WSe2 monolayer are analyzed using photoluminescence and Raman spectroscopy methods. Secondary-ion mass spectrometry is used to perform layer-by-layer chemical analysis of the structure and reveal interlayer diffusion. It is shown that the spintronic emitter fabrication process does not alter key properties of TMDs, which confirms that standard technological procedures preserve the functionality of two-dimensional semiconductor.