  This paper is devoted to photocarrier transport across a two-dimensional
graphene-semiconductor Schottky junction. We study linear response to
monochromatic light with excitation energy well below the semiconductor band
gap. The operation mechanism relies on both photoelectric and thermionic
emission from graphene to a two-dimensional semiconductor under continuous
illumination and zero bias. Due to the thermalization bottleneck for low-energy
carriers in graphene, the photoelectric contribution is found to dominate the
photoresponse at near-infrared excitation frequencies and below. The extended
thermalization time provides an interesting opportunity to facilitate the
interlayer photocarrier transport bypassing the thermalization stage. As a
result, the total photoresponsivity rapidly increases with excitation
wavelength making graphene-semiconductor junctions attractive for
photodetection at the telecommunication frequency.
