Scalable Two-Dimensional Semiconductors—From Photo-Gating to Deep UV Optoelectronics

Two-dimensional semiconductors (2SEM) offer opportunities to advance modern science and technologies. However, transforming the semiconductor landscape requires high-quality materials with well-defined electronic properties, which are still difficult to control and scale. Here, these challenges are addressed by integration of growth, scanning probe microscopy and electron spectroscopy of 2SEM in ultra-high vacuum (UHV). We use a bespoke facility (EPI2SEM) for EPitaxial growth and In-situ analysis of 2SEM in UHV [1]. A centrosymmetric polymorph (D_3d) of gallium selenide (GaSe) is obtained by epitaxy onto large-area sapphire [2] and graphene/SiC [3] substrates. Epitaxial GaSe represents a scalable building block for nanoelectronics. We present two proof-of-concept devices. In our first type of device, the electric dipole at the interface of single layer GaSe and graphene is very sensitive to photogenerated charges in GaSe. The indirect nature of the band gap of GaSe and the heavy hole masses can retard band-to-band recombination and facilitate an accumulation of positive charge in GaSe, thus acting as a photogate for graphene. In the second proof of concept, the grown materials provide a platform for scalable optical sensors. The optical anisotropy and resonant absorption of GaSe in the UV spectrum are exploited for photon sensing in the UV-C spectral range, offering a scalable route to deep-UV optoelectronics [2].<br/>[1] rb.gy/iuaht8; rb.gy/sm21ti<br/>[2] M. Shiffa et al., Small 2024, 20, 2305865.<br/>[3] J. Bradford et al., unpublished 2024.