Abstract <p>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.</p>