  The epitaxial growth of two-dimensional (2D) $\beta-In_2Se_3$ material was
obtained over 2-inches c-sapphire wafers using molecular beam epitaxy (MBE).
Excellent quality of thick (90 nm) and very thin films, down to two quintuple
layers (2 nm), was confirmed by x-ray diffraction (XRD), Raman spectroscopy,
and aberration-corrected scanning transmission electron microscopy (ac-STEM).
Wafer-scale fabrication of photodetectors based on five quintuple layers was
produced using photolithography and other standard semiconductor processing
methods. The photodetectors exhibit responsivity of 3 mA/W, peak specific
detectivity (D*) of $10^9$ Jones, external quantum efficiency (EQE) of 0.67 %
at 550 nm, and response-time of ~7 ms, which is faster than any result
previously reported for $\beta-In_2Se_3$ photodetectors. From the photocurrent
measurements, an optical bandgap of 1.38 eV was observed. These results on
wafer-scale deposition of 2D $In_2Se_3$, as well as its fabrication into
optoelectronic devices provide the missing link that will enable the
commercialization of 2D materials.
