  We have studied the optical properties of two-dimensional (2D) Schottky
photodiode heterojunctions made of chemical vapor deposited (CVD) graphene on
n- and p-type Silicon (Si) substrates. Much better rectification behavior is
observed from the diodes fabricated on n- Si substrates in comparison with the
devices on p-Si substrates in dark condition. Also, graphene/n-Si photodiodes
show a considerable responsivity of 270 mA/W within the silicon spectral range
in DC reverse bias condition. The present results are furthermore compared with
that of a molybdenum disulfide (MoS2)/p-type silicon photodiodes.
