Type-I Heterostructure Based on WS2/PtS2 for High-Performance Photodetectors

High-Performance Broadband Photodetector Based on Tunneling Heterostructure MoS2/PdSe2

The two-dimensional (2D) material PdSe2 is an ideal material for preparing a high-performance broadband photodetector because of its narrow and tunable band gap. However, poor light absorption limits the application of single PdSe2. Here, a PdSe2-based van der Waals (vdWs) heterostructure MoS2/PdSe2 is selected to realize broadband photodetection after a screening of theoretical calculations. Different from most other PdSe2-based heterostructures, MoS2/PdSe2 here is a heterostructure with a type-I band alignment, where the conduction band minimum (CBM) and valence band maximum (VBM) both come from PdSe2. It exhibits high-performance broadband photodetection, for example, in the case of a 600 nm illumination, the heterostructure shows a responsivity of 51.4 A/W and a detectivity of 2.28 × 1010 cm Hz1/2 W-1; in the case of a near-infrared illumination of 900 nm, it has a responsivity of 6.11 A/W and a detectivity of 2.71 × 109 cm Hz1/2 W-1. Our analysis indicates that the good performance originates from a direct tunneling (DT) mechanism in the heterostructure, which not only reduces the recombination of carriers but also improves the carrier collection rate.

Self-Powered Broadband UV-NIR Polarization-Sensitive Photodetector Based on Unipolar van der Waals Heterostructure

van der Waals heterostructures (vdWH) composed of two-dimensional (2D) materials have demonstrated significant potential in new-generation multifunctional photodetectors. Herein, we demonstrate a self-powered broadband polarization-sensitive photodetector with high efficiency and ultrafast response speed based on 2D MoS2/Ta2NiSe5 vdWH, which is due to the unilateral depletion region formed at the n-n junction. Under 638 nm laser illumination, the as-fabricated 2D MoS2/Ta2NiSe5 vdWH photodetector exhibits remarkable photoresponse, including high responsivity (R) of 1382 A/W, large specific detectivity (D*) of 6.59 × 1013 cm Hz1/2 W-1, and impressive external quantum efficiency (EQE) of 2.7 × 105 %, together with ultrafast response time of ∼3 μs. Additionally, the device shows prominent photovoltaic effects with a short-circuit current of 27.4 nA, an open-circuit voltage of 0.28 V, and a maximum output electrical power (Pel) of 1.85 nW, respectively, as well as remarkable self-powered photodetection performance. Interestingly, the device showcases a broadband photoresponse ranging from UV-NIR both under biased and unbiased conditions. Notably, the device also exhibits a robust polarization ratio (PR) of up to 2.89. This study highlights the potential applications of self-powered, broadband, and polarization-sensitive photodetectors based on unipolar vdWH.

Two-dimensional GaN/Si heterojunctions towards high-performance UV-B photodetectors

Two-dimensional (2D) GaN with a tunable bandgap, high electron mobility, and high chemical and thermal stabilities is an ideal choice for high-performance UV-B photodetectors (PDs). However, the realization of 2D GaN based UV-B PDs faces the challenge of simultaneously achieving large-scale preparation and band engineering. In this work, novel UV-B PDs based on wafer-scale 2D GaN/Si heterojunctions have been proposed. Wafer-scale synthesis and band engineering of 2D GaN are realized via a two-step method consisting of magnetron sputtering and high temperature ammonolysis. With well-controlled thickness, the bandgap of 2D GaN is regulated to 3.6 and 4.1 eV. Impressively, novel UV-B PDs based on 2D GaN/Si heterojunctions exhibit a photoresponsivity of 2.2 A W-1 at 308 nm at 1 V, and a fast response speed with a rise/decay time of 1.3/1.1 ms, simultaneously. This work provides a resolution for high-performance UV-B PDs through the controllable growth of 2D GaN, and the proposed synthesis strategy significantly broadens the application prospects of 2D GaN in the field of UV optoelectronics.

A type-I van der Waals heterostructure formed by monolayer WS2 and trilayer PdSe2

Two-dimensional (2D) heterostructures, formed by stacking 2D semiconductors through the van der Waals force, have been extensively studied recently. However, the majority of the heterostructures discovered so far possess type-II interfaces that facilitate interlayer charge separation. Type-I interfaces, on the other hand, confine both electrons and holes in one layer, which is beneficial for optical applications that utilize electron-hole radiative recombination. So far, only a few type-I 2D heterostructures have been achieved, which has limited the construction of multilayer heterostructures with sophisticated band landscapes. Here, we report experimental evidence of a type-I interface between monolayer WS2 and trilayer PdSe2. Two-dimensional PdSe2 has emerged as a promising material for infrared optoelectronic and other applications. We fabricated the heterostructure by stacking an exfoliated monolayer WS2 flake on top of a trilayer PdSe2 film, synthesized by chemical vapor deposition. Photoluminescence spectroscopy measurements revealed that the WS2 exciton peak is significantly quenched in the heterostructure, confirming efficient excitation transfer from WS2 to PdSe2. Femtosecond transient absorption measurements with various pump/probe configurations showed that both electrons and holes photoexcited in the WS2 layer of the heterostructure can efficiently transfer to PdSe2, while neither type of carriers excited in PdSe2 can transfer to WS2. These experimental findings establish a type-I band alignment between monolayer WS2 and trilayer PdSe2. Our results further highlight PdSe2 as an important 2D material for constructing van der Waals heterostructures with emergent electronic and optoelectronic properties.

One-Step Fabrication of 0D Cs4PbBr6 Perovskite with Nonlinear Optical Properties for Ultrafast Pulse Generation

Low-dimensional lead halide perovskites demonstrate remarkable nonlinear optical characteristics attributed to their distinctive physical structures and electronic properties. Nevertheless, the investigation into their nonlinear optical properties remains in its incipient stages. This study addresses this gap by precisely controlling solvent volumes to synthesize both 0D Cs4PbBr6 and Cs4PbBr6/CsPbBr3 perovskites. Remarkably, as saturable absorbers, both pure Cs4PbBr6 and Cs4PbBr6/CsPbBr3 composites exhibit favorable nonlinear optical properties within the C-band, showcasing modulation depths of 9.22% and 16.83%, respectively. Moreover, for the first time, Cs4PbBr6 and Cs4PbBr6/CsPbBr3 composites have been successfully integrated into erbium-doped fiber lasers to realize the mode-locking operations. The utilization of the Cs4PbBr6/CsPbBr3 composites as a saturable absorber that enables the generation of conventional soliton mode-locked laser pulses with a pulse duration of 688 fs, and a repetition frequency of 10.947 MHz at a central wavelength of 1557 nm. Cs4PbBr6 is instrumental in generating laser pulses at a frequency of 10.899 MHz, producing pulse widths of 642 fs at the central wavelength of 1531.2 nm and 1.02 ps at the central wavelength of 1565.3 nm, respectively. The findings of this investigation underscore the potential utility of 0D Cs4PbBr6 and Cs4PbBr6/CsPbBr3 composites as promising materials for optical modulation within fiber laser applications.

Organic-Inorganic Rubrene/WS2 Heterostructure for Broadband Detection and Polarization Imaging

Organic single crystals exhibit improved carrier mobility, longer exciton diffusion length, anisotropic charge transport, and unique linear dichroism, while its high exciton binding energy seriously limits the free-carrier generation and photoelectric conversion efficiency. Layered van der Waals heterostructures, which integrate organic crystals with high mobility two-dimensional (2D) inorganic semiconductors, are promising for promoting exciton dissociation and boosting sensitivity by utilizing the interfacial potential and photogating effect. In this work, organic single-crystal rubrene is integrated with a few-layer WS2 to design the high-performance photodetector. The device exhibits an excellent responsivity of 1000 A W-1, and a fast speed of 180 μs, which is far superior to the individual WS2 device. Equally importantly, this device provides excellent polarization detection performance by virtue of the anisotropic properties of rubrene, and the dichroic ratios are 1.56, 1.5, and 1.7 for 375, 405, and 658 nm irradiation, respectively. Finally, several high-resolution single-pixel broadband polarization imaging was demonstrated. Our work shows that organic-inorganic heterostructure is an essential candidate for improving optoelectronics performance and has potential for polarization imaging.

Two-Dimensional GeS/SnSe2 Tunneling Photodiode with Bidirectional Photoresponse and High Polarization Sensitivity

A two-dimensional (2D) broken-gap (type-III) p-n heterojunction has a unique charge transport mechanism because of nonoverlapping energy bands. In light of this, type-III band alignment can be used in tunneling field-effect transistors (TFETs) and Esaki diodes with tunable operation and low consumption by highlighting the advantages of tunneling mechanisms. In recent years, 2D tunneling photodiodes have gradually attracted attention for novel optoelectronic performance with a combination of strong light-matter interaction and tunable band alignment. However, an in-depth understanding of the tunneling mechanisms should be further investigated, especially for developing electronic and optoelectronic applications. Here, we report a type-III tunneling photodiode based on a 2D multilayered p-GeS/n+-SnSe2 heterostructure, which is first fabricated by the mechanical exfoliation and dry transfer method. Through the Simmons approximation, its various tunneling transport mechanisms dependent on bias and light are demonstrated as the origin of excellent bidirectional photoresponse performance. Moreover, compared to the traditional p-n photodiode, the device enables bidirectional photoresponse capability, including maximum responsivity values of 43 and 8.7 A/W at Vds = 1 and -1 V, respectively, with distinctive photoactive regions from the scanning photocurrent mapping. Noticeably, benefiting from the in-plane anisotropic structure of GeS, the device exhibits an enhanced photocurrent anisotropic ratio of 9, driven by the broader depletion region at Vds = -3 V under 635 nm irradiation. Above all, the results suggest that our designed architecture can be potentially applied to CMOS imaging sensors and polarization-sensitive photodetectors.

High-Performance Broadband Image Sensing Photodetector Based on MnTe/WS2 van der Waals Epitaxial Heterostructures

Two-dimensional transition metal dichalcogenide (TMDC) heterostructure is receiving considerable attention due to its novel electronic, optoelectronic, and spintronic devices with design-oriented and functional features. However, direct design and synthesis of high-quality TMDC/MnTe heterostructures remain difficult, which severely impede further investigations of semiconductor/magnetic semiconductor devices. Herein, the synthesis of high-quality vertically stacked WS2/MnTe heterostructures is realized via a two-step chemical vapor deposition method. Raman, photoluminescence, and scanning transmission electron microscopy characterizations reveal the high-quality and atomically sharp interfaces of the WS2/MnTe heterostructure. WS2/MnTe-based van der Waals field effect transistors demonstrate high rectification behavior with rectification ratio up to 106, as well as a typical p-n electrical transport characteristic. Notably, the fabricated WS2/MnTe photodetector exhibits sensitive and broadband photoresponse ranging from UV to NIR with a maximum responsivity of 1.2 × 103 A/W, a high external quantum efficiency of 2.7 × 105%, and fast photoresponse time of ∼50 ms. Moreover, WS2/MnTe heterostructure photodetectors possess a broadband image sensing capability at room temperature, suggesting potential applications in next-generation high-performance and broadband image sensing photodetectors.

High-performance multilayer WSe2/SnS2p-n heterojunction photodetectors by two step confined space chemical vapor deposition

Two-dimensional (2D) p-n heterojunctions have attracted great attention due to their outstanding properties in electronic and optoelectronic devices, especially in photodetectors. Various types of heterojunctions have been constituted by mechanical exfoliation and stacking. However, achieving controlled growth of heterojunction structures remains a tremendous challenge. Here, we employed a two-step KI-assisted confined-space chemical vapor deposition method to prepare multilayer WSe2/SnS2p-n heterojunctions. Optical characterization results revealed that the prepared WSe2/SnS2vertical heterostructures have clear interfaces as well as vertical heterostructures. The electrical and optoelectronic properties were investigated by constructing the corresponding heterojunction devices, which exhibited good rectification characteristics and obtained a high detectivity of 7.85 × 1012Jones and a photoresponse of 227.3 A W-1under visible light irradiation, as well as a fast rise/fall time of 166/440μs. These remarkable performances are likely attributed to the ultra-low dark current generated in the depletion region at the junction and the high direct tunneling current during illumination. This work demonstrates the value of multilayer WSe2/SnS2heterojunctions for applications in high-performance photodetectors.