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Photodetectors convert light signals into current or voltage outputs and are widely used for imaging, sensing, and spectroscopy. Perovskite-based photodetectors have shown high sensitivity and fast response due to the unprecedented low recombination loss in this solution processed semiconductor. Among various types of CHNHPbI morphology (film, single crystal, nanowire), single-crystalline CHNHPbI nanowires are particularly interesting for photodetection because of their reduced grain boundary, morphological anisotropy, and excellent mechanical flexibility. The concomitant disadvantage associated with the CHNHPbI nanowire photodetectors is their large surface area, which catalyzes carrier recombination and material decomposition, thus significantly degrading device performance and stability. Here we solved this key problem by introducing oleic acid soaking to passivate surface defects of CHNHPbI nanowires, which leads to a device with much improved stability and unprecedented sensitivity (measured detectivity of 2 × 10 Jones). By taking advantage of their one-dimensional geometry, we also showcased, for the first time, the linear dichroic photodetection of our CHNHPbI nanowire photodetector.

Two-dimensional materials (2DMs) have been used widely in constructing photodetectors (PDs) because of their advantages in flexible integration and ultrabroad operation wavelength range. Specifically, 2DM PDs on silicon have attracted much attention because silicon microelectronics and silicon photonics have been developed successfully for many applications. 2DM PDs meet the imperious demand of silicon photonics on low-cost, high-performance, and broadband photodetection. In this work, a review is given for the recent progresses of Si/2DM PDs working in the wavelength band from near-infrared to mid-infrared, which are attractive for many applications. The operation mechanisms and the device configurations are summarized in the first part. The waveguide-integrated PDs and the surface-illuminated PDs are then reviewed in details, respectively. The discussion and outlook for 2DM PDs on silicon are finally given.

A fast silicon-graphene hybrid plasmonic waveguide photodetectors beyond 1.55 μm is proposed and realized by introducing an ultra-thin wide silicon-on-insulator ridge core region with a narrow metal cap. With this novel design, the light absorption in graphene is enhanced while the metal absorption loss is reduced simultaneously, which helps greatly improve the responsivity as well as shorten the absorption region for achieving fast responses. Furthermore, metal-graphenemetal sandwiched electrodes are introduced to reduce the metal-graphene contact resistance, which is also helpful for improving the response speed. When the photodetector operates at 2 μm, the measured 3dB-bandwidth is >20 GHz (which is limited by the experimental setup) while the 3dB-bandwith calculated from the equivalent circuit with the parameters extracted from the measured S 11 is as high as ~100 GHz. To the best of our knowledge, it is the first time to report the waveguide photodetector at 2 μm with a 3dB-bandwidth over 20 GHz. Besides, the present photodetectors also work very well at 1.55 μm. The measured responsivity is about 0.4 A/W under a bias voltage of −0.3 V for an optical power of 0.16 mW, while the measured 3dB-bandwidth is over 40 GHz (limited by the test setup) and the 3 dB-bandwidth estimated from the equivalent circuit is also as high as ~100 GHz, which is one of the best results reported for silicon-graphene photodetectors at 1.55 μm.

Silicon photonics is being extended from the near-infrared window of 1.3-1.5 µm for optical fiber communications to the mid-infrared (mid-IR) wavelength-band of 2 µm or longer for satisfying the increasing demands in many applications. Mid-IR waveguide photodetectors on silicon have attracted intensive attention as one of the indispensable elements for various photonic systems. However, when combining traditional semiconductor materials with silicon, there are some challenges due to lattice mismatch and thermal expansion mismatch. As an alternative, two-dimensional (2D) materials provide a new and promising option for enabling active photonic devices on silicon. Here black-phosphorus (BP) thin films with optimized medium thicknesses (40 nm) are introduced as the active material for light absorption and silicon/BP hybrid ridge waveguide photodetectors at 2 µm are demonstrated with a high responsivity of 306.7 mA W −1 at a low bias voltage of 0.4 V. The 3 dB-bandwidth is up to 1.33 GHz and an experiment of a 4.0 Gbit s −1 data receiving is also demonstrated.

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is time consuming and labor intensive and is not suitable for mass production. Epitaxial growth can produce good-quality graphene while it acquires rigorous conditions and expensive fabrication systems. CVD technique is an effective way to obtain graphene monolayers with large surface areas while it still cannot meet the needs of application. Presently, the reduction of GO stands out as an important strategy for production of graphene. [9] There mainly exist four kinds of oxygen-containing functional groups on GO including hydroxyl (CO), epoxide (COC), carbonyl (CO), and carboxyl (COOH). Hydroxyl and epoxide, located on the basal plane of GO, are the major components, while carbonyl and carboxyl are minor which are distributed at the edges of GO. [10] The nature of the reduction of GO is to remove the oxygen-containing groups from GO. Thermal annealing and chemical reduction are usually used for the reduction of GO. Carboxyl groups can be slowly reduced at 100-150 °C. [11] The high temperature process can remove most of the carbonyl and carboxyl groups by forming CO or CO 2 . [12] There are numerous chemical reducing agents that can be applied for the reduction of GO, for example, borohydrides, [13] hydrohalic acid, [14] nitrogen-containing reducing agents, [15] and so on. Reduction of GO by chemical reducing reagents is based on their chemical reactions. Therefore, we can selectively reduce oxygen-containing groups by choosing specific chemical reducing agents. To date, reduction methods with wellsupported mechanisms mainly include hydrazine hydrate and sodium borohydride. Hydrazine hydrate can open the ring of epoxy groups by forming hydroxyl groups generating dehydroxylation subsequently. [10] Sodium borohydride can turn carbonyl (CO) into hydroxyl (CO) while it does not reduce carboxyl groups, which results in the increasing CO ratio after being reduced. [16] Different reduction processes result in various types and quantities of oxygen-containing groups on the reduced graphene oxide (rGO) with assorted properties, which in turn influences the final performance of materials composed of rGO. Moreover, the biological responses certainly vary depending on the oxygen-containing groups and defects on rGO. Therefore, in this work, GO films were fabricated on the titanium surfaces by cathode electrophoretic deposition, followed by the reduction processes of thermal annealing, hydrazine hydrate, and sodium borohydride chemical reduction. The reduction degrees Graphene can be obtained with the reduction of graphene oxide (GO). Various reduction methods will result in different varieties and amounts of oxygen-containing groups on the reduced graphene oxide (rGO) with diverse properties. In this work, rGO is fabricated on the titanium surfaces by the reduction process of GO through three types of reduction methods, for example, vacuum thermal annealing, hydrazine hydrate, and sodium borohydride chemical reduction. Results show that thermal annealing can remove carboxyl entirely at 600 °C for 1 h, and hydrazine...

Abstract Silicon photonics is becoming more and more attractive in the applications of optical interconnections, optical computing, and optical sensing. Although various silicon photonic devices have been developed rapidly, it is still not easy to realize active photonic devices and circuits with silicon alone due to the intrinsic limitations of silicon. In recent years, two-dimensional (2D) materials have attracted extensive attentions due to their unique properties in electronics and photonics. 2D materials can be easily transferred onto silicon and thus provide a promising approach for realizing active photonic devices on silicon. In this paper, we give a review on recent progresses towards hybrid silicon photonics devices with 2D materials, including two parts. One is silicon-based photodetectors with 2D materials for the wavelength-bands from ultraviolet (UV) to mid-infrared (MIR). The other is silicon photonic switches/modulators with 2D materials, including high-speed electro-optical modulators, high-efficiency thermal-optical switches and low-threshold all-optical modulators, etc. These hybrid silicon photonic devices with 2D materials devices provide an alternative way for the realization of multifunctional silicon photonic integrated circuits in the future.