Group-10 Transition Metal Dichalcogenide Research Articles

Controlled and tunable growth of ambient stable 2D PtS2 thin film and its high-performance broadband photodetectors

PtS2, a group-10 transition metal dichalcogenide (TMDC), has recently attracted enormous interest owing to its tunable band gap (0.25–1.6 eV), high carrier mobility, and large current on-off ratio of the devices. In contrast to other TMDCs, the growth of PtS2 is more difficult, partly due to the nobility of Pt and partly due to the easier formation of the more stable PtS phase rather than PtS2. Herein, we investigate the effect of critical growth parameters like sulfur amount, Pt thickness and gas flow rate for the control and large area growth of PtS2 via thermal assisted conversion process in atmospheric chemical vapour deposition. The detailed characterization using Raman and X-ray photoelectron spectroscopy (XPS) suggests a controlled transition from PtS to PtS2, which can be obtained by fine tuning of these growth parameters. Furthermore, the optimized growth condition of PtS2 is highly reproducible and can be grown on varieties of substrates like SiO2/Si, sapphire, p-type Si, and even on flexible mica substrate. Finally, a high-performance PtS2 photodetector (PD) was fabricated on different substrates. The PD fabricated on SiO2/Si substrate with a detection range covering from visible to NIR region (400–1100 nm) showed a high responsivity and detectivity of 31.38 AW-1 and 3.92 × 1013 Jones, respectively, under 900 nm illumination at a low bias of 1 V. This work demonstrates an effective approach to control the growth of PtS2 on varieties of substrate for high-performance next-generation photodetector for NIR photodetection applications.

Research Process on Photodetectors based on Group-10 Transition Metal Dichalcogenides.

Rapidly evolving group-10 transition metal dichalcogenides (TMDCs) offer remarkable electronic, optical, and mechanical properties, making them promising candidates for advanced optoelectronic applications. Compared to most TMDCs semiconductors, group-10-TMDCs possess unique structures, narrow bandgap, and influential physical properties that motivate the development of broadband photodetectors, specifically infrared photodetectors. This review presents the latest developments in the fabrication of broadband photodetectors based on conventional 2D TMDCs. It mainly focuses on the recent developments in group-10 TMDCs from the perspective of the lattice structure and synthesis techniques. Recent progress in group-10 TMDCs and their heterostructures with different dimensionality of materials-based broadband photodetectors is provided. Moreover, this review accounts for the latest applications of group-10 TMDCs in the fields of nanoelectronics and optoelectronics. Finally, conclusions and outlooks are summarized to provide perspectives for next-generation broadband photodetectors based on group-10 TMDCs.

Nanosecond mid-infrared pulse generation modulated by platinum ditelluride nanosheets

We demonstrated the generation of nanosecond mid-infrared (MIR) pulse from an Er3+-doped ZrF4-BaF2-LaF3-AlF3-NaF (ZBLAN) fiber laser modulated by platinum ditelluride nanosheets experimentally. The platinum ditelluride nanosheets exhibit strong nonlinear absorption with the saturation intensity 46.5 GW cm−2 and modulation depth 27.8% at 2.8 μm wavelength, respectively. With the saturable absorber mirror fabricated by depositing the platinum ditelluride nanosheets on a gold mirror, we have obtained the stable Q-switched pulses with repetition rate of 173.4 kHz and pulse duration of 600 ns at 2.8 μm wavelength under the pump power of 5.6 W. In addition, the maximum average output power and pulse energy reach 591 mW and 3.41 μJ, respectively. The experimental results confirm that the platinum ditelluride nanosheets exhibit excellent nonlinear optical behavior towards the MIR spectral range, and may make inroads towards MIR photonics with group-10 transition-metal dichalcogenides.

In Situ Fabrication of PdSe2/GaN Schottky Junction for Polarization-Sensitive Ultraviolet Photodetection with High Dichroic Ratio.

Polarization-sensitive ultraviolet (UV) photodetection is of great technological importance for both civilian and military applications. Two-dimensional (2D) group-10 transition-metal dichalcogenides (TMDs), especially palladium diselenide (PdSe2), are promising candidates for polarized photodetection due to their low-symmetric crystal structure. However, the lack of an efficient heterostructure severely restricts their applications in UV-polarized photodetection. Here, we develop a PdSe2/GaN Schottky junction by in situ van der Waals growth for highly polarization-sensitive UV photodetection. Owing to the high-quality junction, the device exhibits an appealing UV detection performance in terms of a large responsivity of 249.9 mA/W, a high specific detectivity, and a fast response speed. More importantly, thanks to the puckered structure of the PdSe2 layer, the device is highly sensitive to polarized UV light with a large dichroic ratio up to 4.5, which is among the highest for 2D TMD material-based UV polarization-sensitive photodetectors. These findings further enable the demonstration of the outstanding polarized UV imaging capability of the Schottky junction, as well as its utility as an optical receiver for secure UV optical communication. Our work offers a strategy to fabricate the PdSe2-based heterostructure for high-performance polarization-sensitive UV photodetection.

Microwave surface transport in narrow-bandgap -MOSFETs

Group-10 transition-metal dichalcogenides are puckered van der Waals semiconductors, with a narrow bandgap, envisioned for ultra-broadband infrared (IR) detection. To assess their dynamical transport properties we investigate n-MOSFETs by using microwave admittance spectroscopy. We report on surface channel inversion-depletion-accumulation behaviors with a depletion length of , a mobility of , and a bulk bandgap of . Our 10 µm long devices have an electronic cut-off frequency in the GHz range promising a large gain-bandwidth product, competitive with that of III–V (InAs) and II–VI (HgCdTe) devices. The integration of bulk absorption and surface readout in -MOSFETs is a monolithic geometry suitable for fast IR detection in the application-rich 1– range, which includes molecular spectroscopy, atmospheric communications and thermal sensing.

Electrochemically Exfoliated Platinum Dichalcogenide Atomic Layers for High-Performance Air-Stable Infrared Photodetectors.

Platinum dichalcogenide (PtX2), an emergent group-10 transition metal dichalcogenide (TMD) has shown great potential in infrared photonic and optoelectronic applications due to its layer-dependent electronic structure with potentially suitable bandgap. However, a scalable synthesis of PtSe2 and PtTe2 atomic layers with controlled thickness still represents a major challenge in this field because of the strong interlayer interactions. Herein, we develop a facile cathodic exfoliation approach for the synthesis of solution-processable high-quality PtSe2 and PtTe2 atomic layers for high-performance infrared (IR) photodetection. As-exfoliated PtSe2 and PtTe2 bilayer exhibit an excellent photoresponsivity of 72 and 1620 mA W-1 at zero gate voltage under a 1540 nm laser illumination, respectively, approximately several orders of magnitude higher than that of the majority of IR photodetectors based on graphene, TMDs, and black phosphorus. In addition, our PtSe2 and PtTe2 bilayer device also shows a decent specific detectivity of beyond 109 Jones with remarkable air-stability (>several months), outperforming the mechanically exfoliated counterparts under the laser illumination with a similar wavelength. Moreover, a high yield of PtSe2 and PtTe2 atomic layers dispersed in solution also allows for a facile fabrication of air-stable wafer-scale IR photodetector. This work demonstrates a new route for the synthesis of solution-processable layered materials with the narrow bandgap for the infrared optoelectronic applications.

Facile synthesis of ZnO/PdSe2 core-shell heterojunction for efficient photodetector application

Palladium diselenide (PdSe2), a group-10 transition metal dichalcogenide with great optoelectronic and electrical properties due to unique structure, has gained increasing attention in the scientific community. Herein, we demonstrate an effective strategy to synthesis of ZnO/PdSe2 core–shell heterojunction nanorod arrays (HNAs) through a simple two-step method for the first time. A Pd film was deposited on ZnO NAs by an electron beam evaporation method at first. Then, the selenization process was completed by a chemical vapor deposition (CVD) method. Furthermore, the photoelectric performances of electrodes based on ZnO NAs, PdSe2 film and ZnO/PdSe2 core–shell HNAs were investigated, respectively. The ZnO/PdSe2 core–shell HNA represents better responsitivity with higher photocurrent density (1.3 mA cm−2) comparing to the ZnO NA (0.03 mA cm−2), indicating that the ZnO/PdSe2 samples are more suitable for photoelectric devices. Besides, photoelectric performance of this work is better than most of reported commercial ZnO and ZnO composite nanomaterials.

Improved Performance of Platinum Diselenide Based Surface Plasmon Resonance Biosensor Using Silicon

After the discovery of graphene in 2004, two-dimensional materials have attracted attention at large scale because of their peculiar structure and extraordinary properties. As they have large potential in future nano electronics, two-dimensional transition metal dichalcogenides has become most focus topic of study. Transition metal dichalcogenides with tunable finite band gap and significant transitional behavior are much suitable for the construction of electronic and optoelectronic devices of high-performance. However, platinum diselenide is group-10 transition metal dichalcogenides which occur naturally in one phase transition, which has been theoretically predicted as an excellent material. The proposed structure of surface plasmon resonance (SPR) -based biosensor consists of a silicon and two-dimensional nanomaterial platinum diselenide. The performance parameters of proposed biosensor (surface plasmon resonance-based) such as detection accuracy, figure of merit, sensitivity, full width at half maximum have been investigated. The sensitivity, detection accuracy, full width half maximum and figure of merit of proposed surface plasmon resonance biosensor having silver (50 nm), silicon (2 nm) and one layer of platinum diselenide with 2 nm thickness at 633 nm wavelength is 2200RIU–1 , 0.20 deg–1, 4.980 and 44.22 RIU–1 respectively. Silicon sheet is used in the middle of the Ag and platinum diselenide to prevent the oxidation of silver and enhance the sensitivity of platinum diselenide based surface plasmon resonance biosensor. The sensitivity of conventional surface plasmon resonance biosensor and the proposed surface plasmon resonance biosensor without silicon layer is 1700RIU–1 and 2000RIU–1 respectively. Surface plasmon resonance biosensor of device structure CaF2/Ag/Si/PtSe2 has higher sensitivity in comparison to device structures CaF2/Ag (conventional) and CaF2/Ag/PtSe2 (without Silicon Layer) by 29.41% and 10% respectively. Although the highest sensitivity obtained is 2620RIU–1 for 60 nm silver with 3 nm silicon layer except the platinum diselenide layer.

Direct observation of interlayer coherent acoustic phonon dynamics in bilayer and few-layer PtSe2

This work reports the real-time observation of the interlayer lattice vibrations in bilayer and few-layer PtSe2 by means of the coherent phonon method. The layer-breathing mode and standing wave mode of the interlayer vibrations are found to coexist in such a kind of group-10 transition metal dichalcogenides (TMDCs). The interlayer breathing force constant standing for perpendicular coupling (per effective atom) is derived as 7.5 N/m, 2.5 times larger than that of graphene. The interlayer shearing force constant is comparable to the interlayer breathing force constant, which indicates that PtSe2 has nearly isotropic interlayer coupling. The low-frequency Raman spectroscopy elucidates the polarization behavior of the layer-breathing mode that is assigned to have A1g symmetry. The standing wave mode shows redshift with the increasing number of layers, which successfully determines the out-of-plane sound velocity of PtSe2 experimentally. Our results manifest that the coherent phonon method is a good tool to uncover the interlayer lattice vibrations, beyond the conventional Raman spectroscopy limit. The strong interlayer interaction in group-10 TMDCs reveals their promising potential in high-frequency (∼terahertz) micro-mechanical resonators.

Optical properties of chemical vapor deposition-grown PtSe2 characterized by spectroscopic ellipsometry

PtSe2, an emerging 2D group-10 transition metal dichalcogenide (TMD), has aroused significant attention recently due to its intriguing physical properties. Here, the optical properties of chemical vapor deposition-grown PtSe2 films with different thicknesses were characterized with nondestructive spectroscopic ellipsometry and Fourier transform infrared spectroscopy. The polarized optical microscopy reveals the isotropic in-plane optical response of the continuous PtSe2 films in a scale size of at least as small as 143 × 108 µm2. The electrical transport characterization and UV-mid infrared absorption spectra reveal the coexistence of both semiconducting and metallic contents in these PtSe2 films, making PtSe2 quite different among the 2D material family. The effective refractive index (n) and the extinction coefficient (k) over a spectra range of 360–1700 nm were obtained. In contrast to other TMDs, the values of n and k of PtSe2 were found to have a strong dependence on the thickness and they decrease as the reduction of thickness. This work is conducive to provide vital parameters for further study on PtSe2 and could facilitate its application in optoelectronic devices.

Synthesis of large-scale few-layer PtS2 films by chemical vapor deposition

PtS2, a group-10 transition metal dichalcogenide, has prominent layer-depended band structure, and can enable extremely high phonon-limited mobility at room temperature. Here, we demonstrate the theoretical study on the electronic band structures of PtS2 with different thickness by using density functional theory (DFT), as well as experimental realization of large-area synthesis of few-layer PtS2 film by direct sulfurization of pre-deposited Pt. The synthetic process suggested that the reaction pressure is a key factor in the formation of high-quality PtS2 semiconducting films. Characterizations with atomic force microscopy (AFM), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS) have indicated that good film stoichiometry and uniformity have been achieved. Furthermore, field-effect transistor (FET) arrays were fabricated based on the large-scale PtS2 film, exhibiting well-uniform electrical performance with p-type transport behavior. These results can open up an attractive approach to promote the large-scale applications of PtS2 in advanced nanoelectronics and optoelectronics devices and systems.

Pressure-induced enhancement of optoelectronic properties in PtS2**Project supported by the National Key Research and Development Program of China (Grant Nos. 2018YFA0305700 and 2016YFA0401804), the National Natural Science Foundation of China (Grant Nos. 11574323, 11704387, U1632275, 11304321, 11604340, and 61774136), the Natural Science Foundation of Anhui Province, China (Grant No. 1708085QA19), and the Director’s Fund of Hefei Institutes of Physical Science,

PtS2, which is one of the group-10 transition metal dichalcogenides, attracts increasing attention due to its extraordinary properties under external modulations as predicted by theory, such as tunable bandgap and indirect-to-direct gap transition under strain; however, these properties have not been verified experimentally. Here we report the first experimental exploration of its optoelectronic properties under external pressure. We find that the photocurrent is weakly pressure-dependent below 3 GPa but increases significantly in the pressure range of 3 GPa–4 GPa, with a maximum ∼ 6 times higher than that at ambient pressure. X-ray diffraction data shows that no structural phase transition can be observed up to 26.8 GPa, which indicates a stable lattice structure of PtS2 under high pressure. This is further supported by our Raman measurements with an observation of linear blue-shifts of the two Raman-active modes to 6.4 GPa. The pressure-enhanced photocurrent is related to the indirect-to-direct/quasi-direct bandgap transition under pressure, resembling the gap behavior under compression strain as predicted theoretically.

Ultrafast and sensitive photodetector based on a PtSe2/silicon nanowire array heterojunction with a multiband spectral response from 200 to 1550\u2009nm

The newly discovered Group-10 transition metal dichalcogenides (TMDs) like PtSe2 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 PtSe2 photodetectors integrated with silicon remains undiscovered. Here, we report the successful preparation of large-scale, uniform and vertically grown PtSe2 films by simple selenization method for the design of a PtSe2/Si nanowire array heterostructure, which exhibited a very good photoresponsivity of 12.65 A/W, a high specific detectivity of 2.5 × 1013 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 PtSe2 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 PtSe2/Si nanowire array-based photodetector offers great potential for applications in next-generation optoelectronic and electronic devices.

Electrical devices from top-down structured platinum diselenide films

Platinum diselenide (PtSe2) is an exciting new member of the two-dimensional (2D) transition metal dichalcogenide (TMD) family. It has a semimetal to semiconductor transition when approaching monolayer thickness and has already shown significant potential for use in device applications. Notably, PtSe2 can be grown at low temperature making it potentially suitable for industrial usage. Here, we address thickness-dependent transport properties and investigate electrical contacts to PtSe2, a crucial and universal element of TMD-based electronic devices. PtSe2 films have been synthesized at various thicknesses and structured to allow contact engineering and the accurate extraction of electrical properties. Contact resistivity and sheet resistance extracted from transmission line method (TLM) measurements are compared for different contact metals and different PtSe2 film thicknesses. Furthermore, the transition from semimetal to semiconductor in PtSe2 has been indirectly verified by electrical characterization in field-effect devices. Finally, the influence of edge contacts at the metal–PtSe2 interface has been studied by nanostructuring the contact area using electron beam lithography. By increasing the edge contact length, the contact resistivity was improved by up to 70% compared to devices with conventional top contacts. The results presented here represent crucial steps toward realizing high-performance nanoelectronic devices based on group-10 TMDs.

Wide Spectral Photoresponse of Layered Platinum Diselenide-Based Photodiodes.

Platinum diselenide (PtSe2) is a group-10 transition metal dichalcogenide (TMD) that has unique electronic properties, in particular a semimetal-to-semiconductor transition when going from bulk to monolayer form. We report on vertical hybrid Schottky barrier diodes (SBDs) of two-dimensional (2D) PtSe2 thin films on crystalline n-type silicon. The diodes have been fabricated by transferring large-scale layered PtSe2 films, synthesized by thermally assisted conversion of predeposited Pt films at back-end-of-the-line CMOS compatible temperatures, onto SiO2/Si substrates. The diodes exhibit obvious rectifying behavior with a photoresponse under illumination. Spectral response analysis reveals a maximum responsivity of 490 mA/W at photon energies above the Si bandgap and relatively weak responsivity, in the range of 0.1-1.5 mA/W, at photon energies below the Si bandgap. In particular, the photoresponsivity of PtSe2 in infrared allows PtSe2 to be utilized as an absorber of infrared light with tunable sensitivity. The results of our study indicate that PtSe2 is a promising option for the development of infrared absorbers and detectors for optoelectronics applications with low-temperature processing conditions.

High-performance broadband heterojunction photodetectors based on multilayered PtSe2 directly grown on a Si substrate.

Two-dimensional group-10 transition metal dichalcogenides have recently attracted increasing research interest because of their unique electronic and optoelectronic properties. Herein, we present vertical hybrid heterojunctions of multilayered PtSe2 and Si, which take advantage of large-scale homogeneous PtSe2 films grown directly on Si substrates. These heterojunctions show obvious rectifying behavior and a pronounced photovoltaic effect, enabling them to function as self-driven photodetectors operating at zero bias. The photodetectors can operate in both photovoltage and photocurrent modes, with responsivity values as high as 5.26 × 106 V W-1 and 520 mA W-1 at 808 nm, respectively. The Ilight/Idark ratio, specific detectivity, and response speed are 1.5 × 105, 3.26 × 1013 Jones, and 55.3/170.5 μs, respectively. Furthermore, the heterojunctions are highly sensitive in a broad spectral region ranging from deep ultraviolet to near-infrared (NIR) (200-1550 nm). Because of the strong NIR light absorption of PtSe2, the heterojunctions exhibit photocurrent responsivities of 33.25 and 0.57 mA W-1 at telecommunication wavelengths of 1310 and 1550 nm, respectively. Considering the excellent performance of the PtSe2/Si heterojunctions, they are highly suitable for application in high-performance broadband photodetectors. The generality of the above results also signifies that the proposed in situ synthesis method has great potential for future large-scale optoelectronic device integration.