Abstract
Graphene, a semi-metal with a gapless band structure, has been used in mid-infrared (MIR) photodetectors (PDs) for some time. However, these detectors often suffer from low responsivity due to the intrinsically low absorption and ultra-short carrier lifetime in graphene, large dark current, and low detectivity due to the semi-metallic nature of graphene. Over the past decade, much effort has been devoted to addressing these issues. A variety of metamaterials and related concepts has been employed to improve the detector responsivity by enhancing the graphene absorption and/or the carrier collection efficiency. Here, we provide an overview of the graphene MIR PDs with and without the use of approaches for responsivity enhancement. We focus our attention on the state-of-the-art graphene MIR PDs whose performance is improved by employing metamaterials and related concepts, including band structure engineering, the photogating effect, integration with plasmonic nanostructures and waveguides, the use of asymmetric plasmons, coupled plasmon–phonon polaritons, and small-twist-angle bilayer graphene. We conclude by providing possible directions for further performance improvement of graphene MIR PDs and a discussion on future applications of these detectors.
Highlights
Photodetectors (PDs) convert photon signals into electrical signals, and are key components of modern communication and sensing technologies that play an important role in our daily lives
The development of PDs operating in the visible and near-infrared spectral ranges has reached a high level of maturity due to advances in materials, large-scale production and integration with complementary metal-oxide-semiconductor (CMOS) systems
Room-temperature PDs operating in the mid-infrared (MIR, wavelength: 2.5– 25 μm)2 spectral range are less advanced in terms of integration and pixel counts, despite the important roles that they could play in a wide range of applications, including biosensing,3 security,4
Summary
Photodetectors (PDs) convert photon signals into electrical signals, and are key components of modern communication and sensing technologies that play an important role in our daily lives. Due to its linear electronic dispersion, the Fermi level of graphene and the induced optical response can be strongly modulated via electrostatic gating, which provides an opportunity to achieve gate-tunable photoresponse, e.g. via electrical tuning of the graphene absorption Despite these appealing properties, one of the drawbacks of graphene PDs is the large dark current that traverses the graphene channel when an external bias is applied, due to the semi-metallic nature of graphene. Graphene films can be readily grown by chemical vapor deposition (CVD) methods at low cost and are environmentally friendly, which addresses the aforementioned environmental issues of conventional narrow-bandgap semiconductors These advantages of graphene make it a promising material for construction of MIR PDs. many of the early demonstrations of graphene MIR PDs suffered from low responsivity, due to the low optical absorption (< 2.3 %) and short photocarrier lifetime (sub-picosecond) of this material. We conclude with our thoughts on fruitful future research areas, including further performance enhancements and new applications
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