Wafer‐Scale Two‐Dimensional Semiconductors for Deep UV Sensing

2D semiconductors (2SEM) can transform many sectors, from information and communication technology to healthcare. To date, top‐down approaches to their fabrication, such as exfoliation of bulk crystals by “scotch‐tape,” are widely used, but have limited prospects for precise engineering of functionalities and scalability. Here, a bottom‐up technique based on epitaxy is used to demonstrate high‐quality, wafer‐scale 2SEM based on the wide band gap gallium selenide (GaSe) compound. GaSe layers of well‐defined thickness are developed using a bespoke facility for the epitaxial growth and in situ studies of 2SEM. The dominant centrosymmetry and stacking of the individual van der Waals layers are verified by theory and experiment; their optical anisotropy and resonant absorption in the UV spectrum are exploited for photon sensing in the technological UV‐C spectral range, offering a scalable route to deep‐UV optoelectronics. A bespoke facility for the epitaxial growth and in‐situ characterization of 2D semiconductors is used for wafer scale growth of a novel γ'‐GaSe polymorph. Theory and experiment verify the optical anisotropy and resonant UV absorption of the layers. These properties are exploited for photon sensing in the UV‐C spectral range, offering a scalable route to deep‐UV optoelectronics.