Current status and technological prospect of photodetectors based on two-dimensional materials

Photodetectors are an essential component in a vast number of devices and applications nowadays for they are the cornerstone component of image sensors, ambient sensors in consumer electronics, in spectrometry, biomedical imaging, food and manufacturing process monitoring, just to name a few. The biggest portion of the photodetector market is currently served by silicon (CMOS-based) photodetectors in view of their high performance, low cost, maturity and high level of integration with electronics. Applications that require photodetection in the infrared, i.e., beyond silicon's bandgap, are currently relying on exotic semiconductors such as III-V InGaAs or HgCdTe systems that can cover a spectral beyond 10 mu m. Such technologies, albeit offering high performance detectors, suffer from severe manufacturing costs and integration issues, and therefore are limited only to niche low-volume, high-value markets. This has a major impact on several applications (night vision, infrared spectrometry, infrared imaging) that would provide indispensable information to consumers and automotive industry in terms of health, safety and security. This grand challenge is one that two-dimensional (2D) materials are called for to address, and offer an opportunity to bring about a significant market value growth as well as profound socioeconomic impact. Among the various optoelectronic applications considered for 2D materials, one that has therefore attracted significant attention is that of photodetectors(1). Graphene, an atomically thin semimetallic material with extraordinarily large carrier mobility, flat broadband absorption, and electrostatically tunable carrier concentration, offers unique properties that can be leveraged for photodetection. 2D semiconductor analogs also provide very high carrier mobilities-especially taking into account their nearly atomic thin profiles-and a spectral coverage both in the visible and in the infrared wavelength range, depending upon the material selection. A common additional feature of those materials is their 'form factor' and the resulting possibility to enable high performance optoelectronic devices that are ultra-low-weight, flexible, and therefore suited for seamless integration in a variety of substrates, either rigid or flexible, single crystalline or amorphous etc.