Thermionic graphene/silicon Schottky infrared photodetectors

Optical communications, imaging, and biomedicine require efficient detection of infrared radiation. Growing
demand pushes for the integration of such detectors on chips. It is a challenge for conventional semiconductor
devices to meet these specs due to spectral limitations arising from their finite band gap, as well as material
incompatibilities. Single layer graphene (SLG) is compatible with complementary metal-oxide-semiconductor
(CMOS) Si technology, while its broadband (UV to THz) absorption makes the SLG/Si junction a promising
platform for photodetection. Here we model the thermionic operation of SLG/Si Schottky photodetectors, considering
SLG’s absorption, heat capacity, and carrier cooling dependence on temperature and carrier density. We
self-consistently solve coupled rate equations involving electronic and lattice temperatures, and nonequilibrium
carrier density under light illumination. We use as an example the infrared photon energy of 0.4 eV, below the
threshold for direct photoemission over the Schottky barrier, to study the photothermionic response as a function
of voltage bias, input power, pulse width, electronic injection, and relaxation rates. We find that device and
operation parameters can be optimized to reach responsivities competitive with the state of the art for any light
frequency, unlike conventional semiconductor-based devices. Our results prove that the SLG/Si junction is a
broadband photodetection platform.