Wafer-Scale Two-dimensional Semiconductors for Deep UV Sensing

Two-dimensional semiconductors (2SEM) can transform many sectors, from Information and Communication Technology (ICT) to healthcare. To date, top-down approaches to the 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 epi-taxy 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 (EPI2SEM). 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