Photothermoelectric SnTe Photodetector with Broad Spectral Response and High On/Off Ratio.

A broadband photodetector with high performance is highly desirable for the optoelectric and sensing application. Herein, we report a "photo-thermo-electric" (PTE) detector based on an ultrathin SnTe film. The (001)-oriented SnTe films with the wafer size scale are epitaxially grown on the surface of sodium chloride crystals by a scalable sputtering method. Due to the giant PTE effect under laser spot excitation on the asymmetric position between two terminals, a built-in electrical field is produced to drive bulk carriers for a self-powered photodetector, leading to a broad spectral response in the wavelength range from 404 nm to 10.6 µm far beyond the limitation of the energy band gap. Significantly, the photodetector displays a high on/off photoswitching ratio of over 105 with a suppressed dark current, which is 4-5 orders of magnitude higher than that of other reported SnTe-based detectors. Under zero external bias, the device yields the highest detectivity of ∼1.3 × 1010 cm Hz1/2 W-1 with a corresponding responsivity of ∼3.9 mA W-1 and short rising/falling times of ∼78/84 ms. Furthermore, the photodetector transferred onto the flexible template exhibits excellent mechanical flexibility over 300 bending cycles. These findings offer feasible strategies toward designing and developing low-power-consumption wearable optoelectronics with competitive performance.

Wafer-size growth of 2D layered SnSe films for UV-Visible-NIR photodetector arrays with high responsitivity.

Due to its excellent electrical and optical properties, tin selenide (SnSe), a typical candidate of two-dimensional (2D) semiconductors, has attracted great attention in the field of novel optoelectronics. However, the large-area growth of high-quality SnSe films still remains a great challenge, which limits their practical applications. Here, wafer-size SnSe ultrathin films with high uniformity and crystallization were deposited via a scalable magnetron sputtering method. The results showed that the SnSe photodetector was highly sensitive to a broad range of wavelengths in the UV-visible-NIR range, especially showing an extremely high responsivity of 277.3 A W-1 with the corresponding external quantum efficiency of 8.5 × 104% and detectivity of 7.6 × 1011 Jones. These figures of merits are among the best performances for the sputter-fabricated 2D photodetector devices. The photodetecting mechanisms based on a photogating effect induced by the trapping effect of localized defects are discussed in detail. The results indicate that the few-layered SnSe films obtained from sputtering growth have great potential in the design of high-performance photodetector arrays.

Large Lateral Photovoltaic Effect in MoS2/GaAs Heterojunction.

Molybdenum disulfide (MoS2) nanoscaled films are deposited on GaAs substrates via magnetron sputtering technique, and MoS2/GaAs heterojunctions are fabricated. The lateral photovoltaic effect (LPE) of the fabricated MoS2/GaAs heterojunctions is investigated. The results show that a large LPE can be obtained in the MoS2/n-GaAs heterojunction. The LPE exhibits a linear dependence on the position of the laser illumination and the considerably high sensitivity of 416.4 mV mm-1. This sensitivity is much larger than the values in other reported MoS2-based devices. Comparatively, the LPE in the MoS2/p-GaAs heterojunction is much weaker. The mechanisms to the LPE are unveiled by constructing the energy-band alignment of the MoS2/GaAs heterojunctions. The excellent LPE characteristics make MoS2 films combined with GaAs semiconductors promising candidates for the application of high-performance position-sensitive detectors.

Highly Enhanced H2 Sensing Performance of Few-Layer MoS2/SiO2/Si Heterojunctions by Surface Decoration of Pd Nanoparticles.

A novel few-layer MoS2/SiO2/Si heterojunction is fabricated via DC magnetron sputtering technique, and Pd nanoparticles are further synthesized on the device surface. The results demonstrate that the fabricated sensor exhibits highly enhanced responses to H2 at room temperature due to the decoration of Pd nanoparticles. For example, the Pd-decorated MoS2/SiO2/Si heterojunction shows an excellent response of 9.2 × 103% to H2, which is much higher than the values for the Pd/SiO2/Si and MoS2/SiO2/Si heterojunctions. In addition, the H2 sensing properties of the fabricated heterojunction are dependent largely on the thickness of the Pd-nanoparticle layer and there is an optimized Pd thickness for the device to achieve the best sensing characteristics. Based on the microstructure characterization and electrical measurements, the sensing mechanisms of the Pd-decorated MoS2/SiO2/Si heterojunction are proposed. These results indicate that the Pd decoration of few-layer MoS2/SiO2/Si heterojunctions presents an effective strategy for the scalable fabrication of high-performance H2 sensors.

Self-assembly of C4H-type hydrogenated graphene.

We demonstrate by molecular dynamic (MD) simulations that patterned partially hydrogenated graphene (C4H) can self-assemble at room temperature. The main driving force of the self-assembly of C4H is due to the one-sided distribution of hydrogen and the corresponding asymmetric orientation of sp(3) bonding, there exists strong electrostatic repulsion between the relatively close H atoms. The simulations show that C4H can self-assemble into various carbon nanoscroll (CNS) structures, this is mainly controlled by its geometry (size and aspect ratio). And the carbon nanotube (CNT) is a good candidate to activate and guide C4H to form CNS, whose core size can be controlled. Meanwhile, a novel CNT/C4H core/shell composite nanostructure is also formed. The theoretical results shed important light on a feasible approach to fabricate high-quality CNS and other novel nanostructures including core/shell structures, which hold great potential applications in optics, optoelectronic devices, hydrogen storage, sensors, and energy storage in supercapacitors or batteries.