Polarization-sensitive photodetection in a broad spectrum range is highly desired due to the great significance in military and civilian applications. Palladium diselenide (PdSe2), a newly explored air-stable, group 10 two-dimensional (2D) noble metal dichalcogenide with a puckered pentagonal structure, holds promise for polarization-sensitive photodetection. Herein, we report a highly polarization-sensitive, broadband, self-powered photodetector based on graphene/PdSe2/germanium heterojunction. Owing to the enhanced light absorption of the mixed-dimensional van der Waals heterojunction and the effective carrier collection with graphene transparent electrode, the photodetector exhibits superior device performance in terms of a large photoresponsivity, a high specific detectivity, a fast response speed to follow nanosecond pulsed light signal, and a broadband photosensitivity ranging from deep ultraviolet (DUV) to mid-infrared (MIR). Significantly, highly polarization-sensitive broadband photodetection with an ultrahigh polarization sensitivity of 112.2 is achieved, which represents the best result for 2D layered material-based photodetectors. Further, we demonstrated the high-resolution polarization imaging based on the heterojunction device. This work reveals the great potential of 2D PdSe2 for high-performance, air-stable, and polarization-sensitive broadband photodetectors.

Palladium diselenide (PdSe 2 ), a thus far scarcely studied group-10 transition metal dichalcogenide has exhibited promising potential in future optoelectronic and electronic devices due to unique structures and electrical properties. Here, the controllable synthesis of wafer-scale and homogeneous 2D PdSe 2 film is reported by a simple selenization approach. By choosing different thickness of precursor Pd layer, 2D PdSe 2 with thickness of 1.2-20 nm can be readily synthesized. Interestingly, with the increase in thickness, obvious redshift in wavenumber is revealed by Raman spectroscopy. Moreover, in accordance with density functional theory (DFT) calculation, optical absorption and ultraviolet photoemission spectroscopy (UPS) analyses confirm that the PdSe 2 exhibits an evolution from a semiconductor (monolayer) to semimetal (bulk). Further combination of the PdSe 2 layer with Si leads to a highly sensitive, fast, and broadband photodetector with a high responsivity (300.2 mA W −1 ) and specific detectivity (≈10 13 Jones). By decorating the device with black phosphorus quantum dots, the device performance can be further optimized. These results suggest the asselenized PdSe 2 is a promising material for optoelectronic application.

in optical radar, night vision, military surveillance, and water-quality inspection applications. [1-3] The state-of-theart infrared photodetectors, especially those working in MIR regimes, are fabricated using HgCdTe alloys, [4] InSb, [5] and quantum-wells, [6] which inevitably suffer from strict operation demands, high-cost, and environmental toxicity, thus limiting their widespread usage. [7] Alternatively, two-dimensional (2D) materials have been emerging as ideal candidates for MIR photodetection due to their unique optoelectronic properties and easy integrability. [8] One of the key advantageous features is that the out-of-plane van der Waals (vdW) interaction between layered structures without surface dangling bonds can effectively lower noise from generation-recombination by using the layered materials as main absorbers in MIR regions. [9] For instance, semi-metallic graphene with the ability to absorb light from visible to terahertz enables the design of novel graphene photonic devices that can operate well in mid-wave infrared (MWIR, 3-5 µm), and even in long-wave infrared (LWIR, 8-14 µm) spectral ranges. [10] Unfortunately, the low optical absorption and gapless nature of graphene result in the poor photoresponsivity and large dark current. [11] Although a number of alternative approaches such as integrating quantum dots (QDs), [12] introducing defective states, [13] effective surface doping, [14] and patterning nanoribbon arrays, [15] have been intensively employed to enhance the device performance, they are mainly dominated by uncontrolled processing techniques with time-consuming and complex fabrication procedures. [8] A lately rediscovered black phosphorus (BP) with a large bandgap tunability is widely used for the fabrication of high-sensitivity MIR photodetectors, but its poor air stability leads to the degradation of device performance. Meanwhile, both theoretical and experimental analyses reveal a short cutoff wavelength of ≈3.7 µm for BP-based photodetectors due to its bulk bandgap of ≈0.3 eV, which is far below the second atmospheric window of LWIR photodetection. [16] The existing dilemma stimulates the research community to explore a promising alternative with wide absorption, high air stability, and considerable carrier mobility toward longer-wavelength MIR photodetection. Mid-infrared (MIR) photodetection, covering diverse molecular vibrational regions and atmospheric transmission windows, is vital to civil and military purposes. Versatile use of MIR photodetectors is commonly dominated by HgCdTe alloys, InSb, and quantum superlattices, which are limited by strict operation demands, high-cost, and environmental toxicity. Despite the rapid advances of black phosphorus (BP)-based MIR photodetectors, these are subject to poor stability and large-area integration difficulty. Here, the van der Waals (vdW) epitaxial growth of a wafer-scale 2D platinum ditelluride (PtTe 2) layer is reported via a simple tellurium-vapor transformation approach. The 2D PtTe 2 layer possesses a unique mosaic-like c...

Group-10 layered transitional metal dichalcogenides including PtS2, PtSe2 and PtTe2 are excellent potential candidates for optoelectronic devices due to their unique properties such as high carrier mobility, tunable bandgap, stability and flexibility. Large-area platinum diselenide (PtSe2) with semiconducting characteristics is far scarcely investigated. Here, we report on the development of a high performance photodetector based on vertically aligned PtSe2-GaAs heterojunction which exhibited a broadband sensitivity from deep ultraviolet (DUV) to near infrared (NIR) light, with peak sensitivity from 650 to 810 nm. The Ilight/Idark ratio and responsivity of photodetector were 3×10 4 and 262 mA W −1 measured at 808 nm under zero bias voltage. The response speed of τr/τf were 5.5/6.5 μs, which represented the best result achieved for Group-10 TMDs based optoelectronic device thus far. According to first-principle density functional theory, the broad photoresponse ranging from visible to near infrared region is associated with the semiconducting characteristics of PtSe2 which has interstitial Se atoms within the PtSe2 layers. It was also revealed that the PtSe2/GaAs photodetector did not exhibit performance degradation after 6 weeks in air. The generality of the above good results suggests that the vertically aligned PtSe2 is an ideal material for high-performance optoelectronic systems in the future.

Two-dimensional MoS2 is a promising material for future nanoelectronics and optoelectronics. It has remained a great challenge to grow large-size crystalline and high surface coverage monolayer MoS2. In this work, we investigate the controllable growth of monolayer MoS2 evolving from triangular flakes to continuous thin films by optimizing the concentration of gaseous MoS2, which has been shown a both thermodynamic and kinetic growth factor. A single-crystal monolayer MoS2 larger than 300 μm was successfully grown by suppressing the nuclei density and supplying sufficient source. Furthermore, we present a facile process of transferring the centimeter scale MoS2 assisted with a copper thin film. Our results show the absence of observable residues or wrinkles after we transfer MoS2 from the growth substrates onto flat substrates using this technique, which can be further extended to transfer other two-dimensional layered materials.

The two-dimensional layered semiconducting tungsten disulfide (WS2) film exhibits great promising prospects in the photoelectrical applications because of its unique photoelectrical conversion property. Herein, in this paper, we report the simple and scalable fabrication of homogeneous, large-size and transferable WS2 films with tens-of-nanometers thickness through magnetron sputtering and post annealing process. The produced WS2 films with low resistance (4.2 kΩ) are used to fabricate broadband sensitive photodetectors in the ultraviolet to visible region. The photodetectors exhibit excellent photoresponse properties, with a high responsivity of 53.3 A/W and a high detectivity of 1.22 × 1011 Jones at 365 nm. The strategy reported paves new way towards the large scale growth of transferable high quality, uniform WS2 films for various important applications including high performance photodetectors, solar cell, photoelectrochemical cell and so on.

Wavy shaped PANI/graphene electrodes enable stretchable all-solid-state supercapacitors to maintain high electrochemical capacitance and mechanical strength simutaneously.

The newly discovered Group-10 transition metal dichalcogenides (TMDs) like PtSe 2 have promising applications in high-performance microelectronic and optoelectronic devices due to their high carrier mobilities, widely tunable bandages and ultrastabilities. However, the optoelectronic performance of broadband PtSe 2 photodetectors integrated with silicon remains undiscovered. Here, we report the successful preparation of large-scale, uniform and vertically grown PtSe 2 films by simple selenization method for the design of a PtSe 2 /Si nanowire array heterostructure, which exhibited a very good photoresponsivity of 12.65 A/W, a high specific detectivity of 2.5 × 10 13 Jones at −5 V and fast rise/fall times of 10.1/19.5 μs at 10 kHz without degradation while being capable of responding to high frequencies of up to 120 kHz. Our work has demonstrated the compatibility of PtSe 2 with the existing silicon technology and ultrabroad band detection ranging from deep ultraviolet to optical telecommunication wavelengths, which can largely cover the limitations of silicon detectors. Further investigation of the device revealed pronounced photovoltaic behavior at 0 V, making it capable of operating as a self-powered photodetector. Overall, this representative PtSe 2 /Si nanowire array-based photodetector offers great potential for applications in next-generation optoelectronic and electronic devices.