Jiuxiang Dai

Nature Reviews Methods Primers, Published online: 28 July 2022; doi:10.1038/s43586-022-00139-1

Nature Electronics, Published online: 29 July 2022; doi:10.1038/s41928-022-00798-8

Publication date: September 2022

Source: Materials Today, Volume 58

Author(s): Suchithra Padmajan Sasikala, Sung Hyun Kim, Cheolmin Park, Dong-Ha Kim, Hong Ju Jung, Juhyung Jung, Hojin Lee, Panpan Li, Hongjun Kim, Seungbum Hong, Sung-Yool Choi, Il-Doo Kim, Prem Prabhakaran, Kwang-Sup Lee, Sang Ouk Kim

Nature Communications, Published online: 26 July 2022; doi:10.1038/s41467-022-31763-w

Nature Electronics, Published online: 26 July 2022; doi:10.1038/s41928-022-00818-7

Nature Electronics, Published online: 26 July 2022; doi:10.1038/s41928-022-00814-x

Nature Communications, Published online: 26 July 2022; doi:10.1038/s41467-022-31849-5

Low-dimensional light-emitting materials have presented peculiar optical and optoelectronic properties, unlike their bulk form. The light–matter interaction of these emitters can be engineered by integrating with various planar optical cavities, which is a planar nano- and microstructure that tightly confines light. These integrations provide opportunities for realizing nanophotonic devices based on the new physics allowed by low-dimensional emitters.

Abstract

Low-dimensional light-emitting materials have been actively investigated due to their unprecedented optical and optoelectronic properties that are not observed in their bulk forms. However, the emission from low-dimensional light-emitting materials is generally weak and difficult to use in nanophotonic devices without being amplified and engineered by optical cavities. Along with studies on various planar optical cavities over the last decade, the physics of cavity–emitter interactions as well as various integration methods are investigated deeply. These integrations not only enhance the light–matter interaction of the emitters, but also provide opportunities for realizing nanophotonic devices based on the new physics allowed by low-dimensional emitters. In this review, the fundamentals, strengths and weaknesses of various planar optical resonators are first provided. Then, commonly used low-dimensional light-emitting materials such as 0D emitters (quantum dots and upconversion nanoparticles) and 2D emitters (transition-metal dichalcogenide and hexagonal boron nitride) are discussed. The integration of these emitters and cavities and the expect interplay between them are explained in the following chapters. Finally, a comprehensive discussion and outlook of nanoscale cavity-emitter integrated systems is provided.

Fundamentals of oxide semiconductors are addressed, including a brief history, the function of the constituents and defects, transport mechanisms, and reliability issues. Furthermore, recent achievements of oxide semiconductor transistors are reviewed, and their potential for monolithic 3D integration are introduced. Finally, remaining questions and future directions of oxide semiconductor devices are discussed for next-generation electronics.

Abstract

As Si has faced physical limits on further scaling down, novel semiconducting materials such as 2D transition metal dichalcogenides and oxide semiconductors (OSs) have gained tremendous attention to continue the ever-demanding downscaling represented by Moore's law. Among them, OS is considered to be the most promising alternative material because it has intriguing features such as modest mobility, extremely low off-current, great uniformity, and low-temperature processibility with conventional complementary-metal–oxide–semiconductor-compatible methods. In practice, OS has successfully replaced hydrogenated amorphous Si in high-end liquid crystal display devices and has now become a standard backplane electronic for organic light-emitting diode displays despite the short time since their invention in 2004. For OS to be implemented in next-generation electronics such as back-end-of-line transistor applications in monolithic 3D integration beyond the display applications, however, there is still much room for further study, such as high mobility, immune short-channel effects, low electrical contact properties, etc. This study reviews the brief history of OS and recent progress in device applications from a material science and device physics point of view. Simultaneously, remaining challenges and opportunities in OS for use in next-generation electronics are discussed.

High Thermal Conductivity 2D Materials

In article number 2200409, Fan Wu, He Tian, Chao-yang Xing, Gang Zhang, Tian-Ling Ren, and co-workers discuss high thermal conductivity 2D materials from theory and engineering to applications, especially on graphene and hexagonal boron nitride. The impact factors and development path of 2D materials for thermal dissipation and the engineering aspect of structural design are presented. Moreover, the future opportunities to build 2D-based heat-dissipation systems are discussed.

Author(s): Xiaoyu Xuan, Wanlin Guo, and Zhuhua Zhang

Ferroelasticity is a prominent material property analogous to ferroelectricity and ferromagnetism, but its characteristic spontaneous structural polarization has remained less studied and poorly understood. Here, we use a high-throughput computation approach in conjunction with first-principles calc…

[Phys. Rev. Lett. 129, 047602] Published Fri Jul 22, 2022

The advent of ultrashort optical pulses has provided unprecedented opportunities to probe and manipulate physical properties of quantum materials. There have been rapid growing discoveries of photoinduced new phenomena and nonlinear properties. A review on recent progress of ultrafast optical characterization and manipulation of quantum states, specifically in systems with broken-symmetry states or phase transitions, and prospects are provided.

Abstract

The advent of intense ultrashort optical pulses spanning a frequency range from terahertz to the visible has opened a new era in the experimental investigation and manipulation of quantum materials. The generation of strong optical field in an ultrashort time scale enables the steering of quantum materials nonadiabatically, inducing novel phenomenon or creating new phases which may not have an equilibrium counterpart. Ultrafast time-resolved optical techniques have provided rich information and played an important role in characterization of the nonequilibrium and nonlinear properties of solid systems. Here, some of the recent progress of ultrafast optical techniques and their applications to the detection and manipulation of physical properties in selected quantum materials are reviewed. Specifically, the new development in the detection of the Higgs mode and photoinduced nonequilibrium response in the study of superconductors by time-resolved terahertz spectroscopy are discussed.

An interesting phenomenon in that Te nanowires (NWs) behave with a negative photoresponse to positive photoresponse under enlarged optical intensities from the UV to VIS–IR region is reported. The inverse photoconductance can be attributed to the competition between the photoconductive effect and oxygen desorption effect. Moreover, the influence of the size of Te NWs and their layers is also discussed.

Abstract

As a typical p-type semiconductor, tellurium (Te) has been widely studied for the construction of photodetectors. However, only the positive photoconductance of Te-based photodetectors based on the photoconductive effect has been observed in the reported literature. Herein, an unusual but interesting phenomenon, in that tellurium nanowires (NWs) behave with negative photoresponse to positive photoresponse under enlarged optical intensities from the UV to VIS–IR region is reported. According to the experiments and simulations, adsorbed oxygen on the surface of Te NWs plays a significant role in the abnormal photoresponse. The inverse photoconductance can be attributed to the competition between the photoconductive effect and the oxygen desorption effect. Moreover, the influence of the size and layers of Te NWs is also discussed. This inverse photoconductance phenomenon is further explored by introducing the Te–Au heterojunction system. Hot-electron injection at the Te–Au heterojunction interface induces a more obvious tendency to behave with a negative photoresponse. These findings will be beneficial for potential applications of Te-NW-based photodetectors.

Nature, Published online: 20 July 2022; doi:10.1038/d41586-022-01941-3

The authors utilize a selective e-beam irradiation to pattern the doping profile of oxidized p⁺-WSe₂ field-effect transistors (FETs), overcoming the key challenge of surface charge transfer doping. Seamless lateral junction p-FETs are realized with high on/off ratio (10⁹) and saturation current (−280 μA µm⁻¹), which are crucial for designing logic circuits.

Abstract

Surface charge transfer doping (SCTD) using oxygen plasma to form a p-type dopant oxide layer on transition metal dichalcogenide (TMDs) is a promising doping technique for 2D TMDs field-effect transistors (FETs). However, patternability of SCTD is a key challenge to effectively switch FETs. Herein, a simple method to selectively pattern degenerately p-type (p⁺)-doped WSe₂ FETs via electron beam (e-beam) irradiation is reported. The effect of the selective e-beam irradiation is confirmed by the gate-tunable optical responses of seamless lateral p⁺–p diodes. The OFF state of the devices by inducing trapped charges via selective e-beam irradiation onto a desired channel area in p⁺-doped WSe₂, which is in sharp contrast to globally p⁺-doped WSe₂ FETs, is realized. Selective e-beam irradiation of the PMMA-passivated p⁺-WSe₂ enables accurate control of the threshold voltage (V _th) of WSe₂ devices by varying the pattern size and e-beam dose, while preserving the low contact resistance. By utilizing hBN as the gate dielectric, high-performance WSe₂ p-FETs with a saturation current of −280 µA µm⁻¹ and on/off ratio of 10⁹ are achieved. This study's technique demonstrates a facile approach to obtain high-performance TMD p-FETs by e-beam irradiation, enabling efficient switching and patternability toward various junction devices.

A mixed-dimensional van der Waals graphene/perovskite detector is fabricated by directly growing single-crystal hybrid perovskite on graphene. Due to the strong interface coupling, this self-driven hybrid device exhibits remarkable comprehensive performance, including a fast response speed (2.05 μs) and high responsivity (10.41 A W⁻¹) and detectivity (4.65 × 10¹² Jones).

Abstract

Mixed-dimensional (2D/3D) van der Waals (vdW) heterostructures made with complementary materials hold a lot of promise in the field of optoelectronic devices. Beyond simple mechanical stacking, directly growing the single-crystal perovskite on 2D materials to construct a high-quality vdW heterojunction can better promote carrier transport. In this work, a monolithic integrated graphene/perovskite heterojunction device is fabricated by directly growing a single-crystal hybrid perovskite on monolayer graphene. Due to the strong interface coupling, the hybrid device achieves self-powering behavior and exhibits prominent photoresponse properties with a fast response speed of up to 2.05 μs. Moreover, the responsivity and detectivity can be boosted to up to 10.41 A W⁻¹ and 4.65 × 10¹² Jones under the actuation of −3 V bias. This technique not only improves the device performance, but also provides an effective guideline for the development of next-generation directly integrated vdW optoelectronic devices.

A self-powered bifunctional perovskite photodetector that can operate in both broadband and narrowband regimes is successfully fabricated by an additive-containing spin-coating method combined with post-treatment. The bifunctional behavior is attributed to the morphology-dependent carrier recombination and separation transport capability of the perovskite film for different wavelengths of light. We employ the bifunctional behavior to achieve double encryption during signal transmission.

Abstract

Photodetectors generally operate exclusively in either the broadband or narrowband. Developing bifunctional photodetectors that can detect photons in both broadband and narrowband would bring significant versatility to the optoelectronic platform. Nevertheless, the design of bifunctional integrated devices remains challenging due to the differentiated strategies with respect to device structure and material combination. Herein, we propose introducing polyvinylpyrrolidone to increase the viscosity of the perovskite precursor solution, which introduces abundant defects and cavities into the perovskite film while maintaining a relatively low film thickness. Then, we use methylamine gas to postprocess the middle area of the film to promote directional recrystallization and densification, thereby realizing narrowband and broadband dual-function photodetection in a single device at zero bias. Both ends of the film exhibit a near-infrared peak response at 780 nm with a narrow full-width at half maximum of approximately 30 nm without an external bias. The middle broadband photodetector exhibits a high responsivity of 329 mA W⁻¹ and EQE up to 52.46% at 780 nm. We make full use of narrow-band wavelength selective detection and broadband full-spectrum detection to achieve double encryption during signal transmission. This work represents an important step toward the realization of perovskite-based multifunctional integrated devices.

Two-dimensional (2D) In₂Se₃ is a novel ferroelectric capable of fighting against the depolarization field at nanoscale. Thus, 2D In₂Se₃-based low-power consumption, high-density ferroelectric devices are promising candidates for data storage applications. This review summarizes the major advances in 2D In₂Se₃, including structures, properties, phase/switching transitions, and device performance. Prospects for its future development and research directions are also presented.

Abstract

Ferroelectric memory is a promising candidate for next-generation nonvolatile memory owing to its outstanding performance such as low power consumption, fast speed, and high endurance. However, the ferroelectricity of conventional ferroelectric materials will be eliminated by the depolarization field when the size drops to the nanometer scale. As a result, the miniaturization of ferroelectric devices was hindered, which makes ferroelectric memory unable to keep up with the development of integrated-circuit (IC) miniaturization. Recently, a two-dimensional (2D) In₂Se₃ was reported to maintain stable ferroelectricity at the ultrathin scale, which is expected to break through the bottleneck of miniaturization. Soon, devices based on 2D In₂Se₃, including the ferroelectric field-effect transistor, ferroelectric channel transistor, synaptic ferroelectric semiconductor junction, and ferroelectric memristor were demonstrated. However, a comprehensive understanding of the structures and the ferroelectric-switching mechanism of 2D In₂Se₃ is still lacking. Here, the atomic structures of different phases, the dynamic mechanism of ferroelectric switching, and the performance/functions of the latest devices of 2D In₂Se₃ are reviewed. Furthermore, the correlations among the structures, the properties, and the device performance are analyzed. Finally, several crucial problems or challenges and possible research directions are put forward. We hope that this review paper can provide timely knowledge and help for the research community to develop 2D In₂Se₃ based ferroelectric memory and computing technology for practical industrial applications.