  Two-dimensional (2D) materials have attracted substantial attention in
electronic and optoelectronic applications with superior advantages of being
flexible, transparent and highly tunable. Gapless graphene exhibits
ultra-broadband and fast photoresponse while the 2D semiconducting MoS2 and
GaTe unveil high sensitivity and tunable responsivity to visible light.
However, the device yield and the repeatability call for a further improvement
of the 2D materials to render large-scale uniformity. Here we report a
layer-by-layer growth of wafer-scale GaTe with a hole mobility of 28.4 cm2/Vs
by molecular beam epitaxy. The arrayed p-n junctions were developed by growing
few-layer GaTe directly on three-inch Si wafers. The resultant diodes reveal
good rectifying characteristics, photoresponse with a maximum photoresponsivity
of 2.74 A/W and a high photovoltaic external quantum efficiency up to 62%. The
photocurrent reaches saturation fast enough to capture a time constant of 22
{\mu}s and shows no sign of device degradation after 1.37 million cycles of
operation. Most strikingly, such high performance has been achieved across the
entire wafer, making the volume production of devices accessible. Finally,
several photo-images were acquired by the GaTe/Si photodiodes with a reasonable
contrast and spatial resolution, demonstrating for the first time the potential
of integrating the 2D materials with the silicon technology for novel
optoelectronic devices.
