Ultra-sensitive graphene-bismuth telluride nano-wire hybrids for infrared detection

2D materials-based photodetectors combined with ferroelectrics

Photodetectors are essential optoelectronic devices that play a critical role in modern technology by converting optical signals into electrical signals, which are one of the most important sensors of the informational devices in current 'Internet of Things' era. Two-dimensional (2D) material-based photodetectors have excellent performance, simple design and effortless fabrication processes, as well as enormous potential for fabricating highly integrated and efficient optoelectronic devices, which has attracted extensive research attention in recent years. The introduction of spontaneous polarization ferroelectric materials further enhances the performance of 2D photodetectors, moreover, companying with the reduction of power consumption. This article reviews the recent advances of materials, devices in ferroelectric-modulated photodetectors. This review starts with the introduce of the basic terms and concepts of the photodetector and various ferroelectric materials applied in 2D photodetectors, then presents a variety of typical device structures, fundamental mechanisms and potential applications under ferroelectric polarization modulation. Finally, we summarize the leading challenges currently confronting ferroelectric-modulated photodetectors and outline their future perspectives.

Pollution-free interface of 2D-MoS2/1D-CuO vdWs heterojunction for high-performance photodetector

Van der Waals heterostructures provide a new opportunity for constructing new structures and improving the performance of electronic and optoelectronic devices. However, the existing methods of constructing heterojunctions are still faced with problems such as impurity introduction, or complex preparation process and limited scope of application. Herein, a physisorption method is proposed to composite CuO nanorods on the surface of MoS2nanosheets. CuO nanorods and MoS2form type-Ⅱ heterojunctions, which promotes the separation and transport of photo-generated charge carriers. More importantly, compared with the transfer and coating methods, the physical adsorption method avoids the introduction of auxiliary materials during the whole process of constructing the heterojunction, and therefore effectively reduces the damage and pollution at the interface. The optimized MoS2/CuO heterojunction photodetector achieves a high photoresponsivity of ∼680.1 A W-1and a fast response speed of ∼29μs. The results demonstrate that the physisorption method provides a feasible approach to realize high performance photodetectors with pollution-free interfaces, and it can also be extended to the development of other low-dimensional hybrid heterojunction electronic and optoelectronic devices.

High-Performance Broad-Band Photodetection Based on Graphene-MoS2xSe2(1-x) Alloy Engineered Phototransistors

The concept of alloy engineering has emerged as a viable technique toward tuning the band gap as well as engineering the defect levels in two-dimensional transition-metal dichalcognides (TMDCs). The possibility of synthesizing these ultrathin TMDC materials through a chemical route has opened up realistic possibilities to fabricate hybrid multifunctional devices. By synthesizing nanosheets with different composites of MoS_2xSe_2(1-x) (x = 0 - 1) using simple chemical methods, we systematically investigate the photoresponse properties of three terminal hybrid devices by decorating large-area graphene with these nanosheets (x = 0, 0.5, 1) in 2D-2D configurations. Among them, the graphene-MoSSe hybrid phototransistor exhibits optoelectronic properties superior to those of its binary counterparts. The device exhibits extremely high photoresponsivity (>10⁴ A/W), low noise equivalent power (∼10^-14 W/Hz^0.5), and higher specific detectivity (∼10¹¹ jones) in the wide UV-NIR (365-810 nm) range with excellent gate tunability. The broad-band light absorption of MoSSe, ultrafast charge transport in graphene, and controllable defect engineering in MoSSe makes this device extremely attractive. Our work demonstrates the large-area scalability with the wafer-scale production of MoS_2xSe_2(1-x) alloys, having important implications toward the facile and scalable fabrication of high-performance optoelectronic devices and providing important insights into the fundamental interactions between van der Waals materials.

High-Efficiency Infrared Sensing with Optically Excited Graphene-Transition Metal Dichalcogenide Heterostructures

Binary van der Waals heterostructures of graphene (Gr) and transition metal dichalcogenide (TMDC) have evolved as a promising candidate for photodetection with very high responsivity due to the separation of photo-excited electron-hole pairs across the interface. The spectral range of optoelectronic response in such hybrids has so far been limited by the optical bandgap of the light absorbing TMDC layer. Here, the bidirectionality of interlayer charge transfer is utilized for detecting sub-band gap photons in Gr-TMDC heterostructures. A Gr/MoSe₂ heterostructure sequentially driven by visible and near infra-red (NIR) photons is employed, to demonstrate that NIR induced back transfer of charge allows fast and repeatable detection of the low energy photons (less than the optical band gap of the TMDC layer). This mechanism provides photoresponsivity as high as ≈3000 A W^-1 close to the communication wavelength. The experiment provides a new strategy for achieving highly efficient photodetection over a broad range of energies beyond the spectral bandgap with the 2D semiconductor family.

All-Optical and One-Color Rewritable Chemical Patterning on Pristine Graphene under Water

We report a facile all-optical method for spatially resolved and reversible chemical modification of a graphene monolayer. A tightly focused laser on graphene under water introduces an sp³-type chemical defect by photo-oxidation. The sp³-type defects can be reversibly restored to sp² carbon centers by the same laser with higher intensity. The photoreduction occurs due to laser-induced local heating on the graphene. These optical methods combined with a laser direct writing technique allow photowriting and erasing of a well-defined chemical pattern on a graphene canvas with a spatial resolution of about 300 nm. The pattern is visualized by Raman mapping with the same excitation laser, enabling an optical read-out of the chemical information on the graphene. Here, we successfully demonstrate all-optical Write/Read-out/Erase of chemical functionalization patterns on graphene by simply adjusting the one-color laser intensity. The all-optical method enables flexible and efficient tailoring of physicochemical properties in nanoscale for future applications.

Self-powered topological insulator Bi2Te3/Ge heterojunction photodetector driven by long-lived excitons transfer

Due to the wide spectral absorption and ultrafast electron dynamical response under optical excitation, topological insulator (TI) was proposed to have appealing application in next-generation photonic and optoelectronic devices. Whereas, the bandgap-free speciality of Dirac surface states usually leads to a quick relaxation of photoexcited carriers, making the transient excitons difficult to manipulate in isolated TIs. Growth of TI Bi₂Te₃/Ge heterostructures can promote the specific lifetime and quantity of long-lived excitons, offering the possibility of designing original near-infrared optoelectronic devices, however, the construction of TI Bi₂Te₃/Ge heterostructures has yet to be investigated. Herein, the high-quality Bi₂Te₃/Ge heterojunction with clear interface was prepared by physical vapor deposition strategy. A significant photoluminescence quenching behaviour was observed by experiments, which was attributed to the spontaneous excitation transfer of electrons at heterointerface via theoretical analysis. Then, a self-powered heterostructure photodetector was fabricated, which demonstrated a maximal detectivity of 1.3 × 10¹¹Jones, an optical responsivity of 0.97 A W^-1, and ultrafast photoresponse speed (12.1μs) under 1064 nm light illumination. This study offers a fundamental understanding of the spontaneous interfacial exciton transfer of TI-based heterostructures, and the as-fabricated photodetectors with excellent performance provided an important step to meet the increasing demand for novel optoelectronic applications in the future.

Engineering sensitivity and spectral range of photodetection in van der Waals materials and hybrids

Exploration of van der Waals heterostructures in the field of optoelectronics has produced photodetectors with very high bandwidth as well as ultra-high sensitivity. Appropriate engineering of these heterostructures allows us to exploit multiple light-to-electricity conversion mechanisms, ranging from photovoltaic, photoconductive to photogating processes. These mechanisms manifest in different sensitivity and speed of photoresponse. In addition, integrating graphene-based hybrid structures with photonic platforms provides a high gain-bandwidth product, with bandwidths ≫1 GHz. In this review, we discuss the progression in the field of photodetection in 2D hybrids. We emphasize the physical mechanisms at play in diverse architectures and discuss the origin of enhanced photoresponse in hybrids. Recent developments in 2D photodetectors based on room temperature detection, photon-counting ability, integration with Si and other pressing issues, that need to be addressed for these materials to be integrated with industrial standards have been discussed.

Photodetectors of 2D Materials from Ultraviolet to Terahertz Waves

2D materials are considered to be the most promising materials for photodetectors due to their unique optical and electrical properties. Since the discovery of graphene, many photodetectors based on 2D materials have been reported. However, the low quantum efficiency, large noise, and slow response caused by the thinness of 2D materials limit their application in photodetectors. Here, recent progress on 2D material photodetectors is reviewed, covering the spectrum from ultraviolet to terahertz waves. First the interaction of 2D materials with light is analyzed in terms of optical physics. Then the present methods to improve the performance of 2D material photodetectors are summarized, such as defect engineering, p-n junctions and hybrid detectors, and the issue of serious overestimation of the performance in reported photodetectors based on 2D materials is discussed. Next, a comparison of 2D material photodetectors with traditional commercially available detectors shows that it is difficult to balance the current 2D material photodetectors with regard to having simultaneously both high sensitivity and fast response. Finally, a possible novel EIW mechanism is suggested to advance the performance of 2D material photodetectors in the future.

Designing complex radial heterostructures of Te/Bi2Te3 and Te/Bi2-x Pb x Te3 nanowires: fundamental mechanistic insights into nanowire growth and evolution

Metal telluride/Te heterostructure nanowires are important thermoelectric materials and it is important to be able to tune these materials according to the requirement of the application. In order to do so, a good understanding of the reaction mechanism and critical observation of the evolution of the nanowire heterostructure during the course of reaction is essential. Here, single crystalline, anisotropic Te core/Bi2Te3 shell nanowires have been synthesized by a facile template-based wet chemical synthesis method. The formation and evolution mechanism of the heterostructure has been elucidated by several control reactions, detailed transmission electron microscopy imaging and composition analysis using energy dispersive spectroscopy in scanning transmission electron microscopy mode of the products of the reactions. Fundamental understanding of the formation mechanism and time-dependent evolution of the core-shell structure in the nanowire have led to successful designing of higher order heterostructures involving Te/Bi2-x Pb x Te3. Through this study, interesting insights into the crystal structure evolution, crystal growth and miscibility of PbTe and Bi2Te3 into each other is obtained.

High performance broadband photodetectors based on Sb2Te3/n-Si heterostructure

With the rapid development of optoelectronic devices, photodetectors have triggered unprecedented promise in the field of optical communication, environmental monitoring, biological imaging, chemical sensing. At the same time, there is a higher requirement for photodetectors. It is still a huge challenge for photodetectors that possess excellent performance, low cost and broad range photoresponse from ultraviolet to infrared. In this work, a facile, low cost growth of Sb₂Te₃ thin film using magnetic sputtering was performed. After rapid annealing treatment, the crystallinity of the thin film was transformed from amorphous to polycrystalline. Ultraviolet-visible-infrared absorption study of the thin film revealed broad absorption range, which is ideal for use in broadband photodetectors. Such photodetectors can find many important applications in communication, data security, environmental monitoring and defense technology etc. A prototype photodetector, consisting of Sb₂Te₃/n-Si heterostructure, was produced and characterized. The device demonstrated a significant photoelectric response at a broad spectral range of between 250 and 2400 nm. The maximum responsivity and detectivity of the device were 270 A W^-1 and 1.28 × 10¹³ Jones, respectively, under 2400 nm illumination. Therefore, the results showed the potential use of Sb₂Te₃ thin film in developing high performance broadband photodetectors.

Photo-induced electrodeposition of metallic nanostructures on graphene

Graphene, a single atomic layer of sp2 hybridized carbon, is a promising material for future devices due to its excellent optical and electrical properties. Nevertheless, for practical applications, it is essential to deposit patterned metals on graphene in the micro and nano-meter scale in order to inject electrodes or modify the 2D film electrical properties. However, conventional methods for depositing patterned metals such as lift-off or etching leave behind contamination. This contamination has been demonstrated to deteriorate the interesting properties of graphene such as its carrier mobility. Therefore, to fully exploit the unique properties of graphene, the controlled and nano-patterned deposition of metals on graphene films without the use of a sacrificial resist is of significant importance for graphene film functionalization and contact deposition. In this work, we demonstrate a practical and low-cost optical technique of direct deposition of metal nano-patterned structures without the need for a sacrificial lift-off resist. The technique relies on the laser induced reduction of metal ions on a graphene film. We demonstrate that this deposition is optically driven, and the resolution is limited only by the diffraction limit of the light source being used. Patterned metal features as small as 270 nm in diameter are deposited using light with a wavelength of 532 nm and a numerical aperture of 1.25. Deposition of different metals such as Au, Ag, Pd, Pb and Pt is shown. Additionally, change in the Fermi level of the graphene film through the nano-patterned metal is demonstrated through the electrical characterization of four probe field effect transistors.

2D material broadband photodetectors

Our review provides a comprehensive overview of the latest evolution of broadband photodetectors (BBPDs) based on 2D materials (2DMs). We begin with BBPDs built on various 2DM channels, including narrow-bandgap 2DMs, 2D topological semimetals, 2D charge density wave compounds, and 2D heterojunctions. Then, we introduce defect-engineered 2DM BBPDs, including vacancy engineering, heteroatom incorporation, and interfacial engineering. Subsequently, we summarize 2DM based mixed-dimensional (0D-2D, 1D-2D, 2D-3D, and 0D-2D-3D) BBPDs. Finally, we provide several viewpoints for the future development of this burgeoning field.