Abstract
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.
Highlights
Efficient light detection in the infrared (IR) is key to a variety of applications ranging from optical communications [1,2], imaging [3], biomedicine [4,5], tomography [6], and more
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
We fist consider Single layer graphene (SLG) on a n-Si substrate illuminated by a 1.5 ps pulse at λ = 3.1 μm at peak power Pin = 108 W/cm2
Summary
Efficient light detection in the infrared (IR) is key to a variety of applications ranging from optical communications [1,2], imaging [3], biomedicine [4,5], tomography [6], and more. The lower density of states in SLG [70] compared to bulk metals leads to SLG Fermi level (EF ) shifts upon doping [71], enabling the control of the SBH beyond the classical Schottky effect [9,72] of barrier lowering [9,14], by application of an external electric field via gating [73], and/or a reverse voltage bias [74,75] This electrical tuning of SBH provides an extra degree of freedom for optimizing the PTh response in SLG/SC PDs and allows one to reach ∼100% optical absorption in SLG when the device is integrated into an optical cavity [76–80] by adjusting SLG absorption (i.e., optical loss) toward the critical coupling condition (loss rate equal to cavity decay rate) [76,77]. We provide in the Supplemental Material a detailed table of acronyms and symbols definition, which is useful for the rest of this paper
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