A self-powered, high-performance Ti3 C2 Tx MXene/GaN van der Waals heterojunction (vdWH)-based ultraviolet (UV) photodiode is reported. Such integration creates a Schottky junction depth that is larger than the UV absorption depth to sufficiently separate the photoinduced electron/hole pairs, boosting the peak internal quantum efficiency over the unity and the external quantum efficiency over 99% under weak UV light without bias. The proposed Ti3 C2 Tx /GaN vdWH UV photodiode demonstrates pronounced photoelectric performances working in self-powered mode, including a large responsivity (284 mA W-1 ), a high specific detectivity (7.06 × 1013 Jones), and fast response speed (rise/decay time of 7.55 µs/1.67 ms). Furthermore, the remarkable photovoltaic behavior leads to an impressive power conversion efficiency of 7.33% under 355 nm UV light illumination. Additionally, this work presents an easy-processing spray-deposition route for the fabrication of large-area UV photodiode arrays that exhibit highly uniform cell-to-cell performance. The MXene/GaN photodiode arrays with high-efficiency and self-powered ability show high potential for many applications, such as energy-saving communication, imaging, and sensing networks.

Self-Powered MXene/GaN van der Waals Heterojunction Ultraviolet Photodiodes with Superhigh Efficiency and Stable Current Outputs

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 (PtTe2 ) layer is reported via a simple tellurium-vapor transformation approach. The 2D PtTe2 layer possesses a unique mosaic-like crystal structure consisting of single-crystal domains with highly preferential [001] orientation along the normal direction, reducing the influence of interface defects and ensuring efficient out-of-plane carrier transportation. This characteristic, combined with the wide absorption of PtTe2 and well-designed vertical device architecture, makes the PtTe2 /Si Schottky junction photodetector capable of sensing ultra-broadband light of up to 10.6 µm with a high specific detectivity. Also, the photodetector exhibits an excellent room-temperature infrared-imaging capability. This approach provides a new design concept for high-performance, room-temperature MIR photodetection based on 2D layered materials.

Van der Waals Epitaxial Growth of Mosaic‐Like 2D Platinum Ditelluride Layers for Room‐Temperature Mid‐Infrared Photodetection up to 10.6 µm

Broadband photodetectors are of great importance for numerous optoelectronic applications. Two-dimensional (2D) tungsten disulfide (WS2), an important family member of transition-metal dichalcogenides (TMDs), has shown great potential for high-sensitivity photodetection due to its extraordinary properties. However, the inherent large bandgap of WS2 and the strong interface recombination impede the actualization of high-sensitivity broadband photodetectors. Here, we demonstrate the fabrication of an ultrabroadband WS2/Ge heterojunction photodetector through defect engineering and interface passivation. Thanks to the narrowed bandgap of WS2 induced by the vacancy defects, the effective surface modification with an ultrathin AlOx layer, and the well-designed vertical n-n heterojunction structure, the WS2/AlOx/Ge photodetector exhibits an excellent device performance in terms of a high responsivity of 634.5 mA/W, a large specific detectivity up to 4.3 × 1011 Jones, and an ultrafast response speed. Significantly, the device possesses an ultrawide spectral response spanning from deep ultraviolet (200 nm) to mid-wave infrared (MWIR) of 4.6 μm, along with a superior MWIR imaging capability at room temperature. The detection range has surpassed the WS2-based photodetectors in previous reports and is among the broadest for TMD-based photodetectors. Our work provides a strategy for the fabrication of high-performance ultrabroadband photodetectors based on 2D TMD materials.

Ultrabroadband and High-Detectivity Photodetector Based on WS2/Ge Heterojunction through Defect Engineering and Interface Passivation.

Production of large-area 2D materials for high-performance photodetectors by pulsed-laser deposition

There is an emerging need for high-sensitivity solar-blind deep ultraviolet (DUV) photodetectors with an ultra-fast response speed. Although nanoscale devices based on Ga2O3 nanostructures have been developed, their practical applications are greatly limited by their slow response speed as well as low specific detectivity. Here, the successful fabrication of two-/three-dimensional (2D/3D) graphene (Gr)/PtSe2/β-Ga2O3 Schottky junction devices for high-sensitivity solar-blind DUV photodetectors is demonstrated. Benefitting from the high-quality 2D/3D Schottky junction, the vertically stacked structure, and the superior-quality transparent graphene electrode for effective carrier collection, the photodetector is highly sensitive to DUV light illumination and achieves a high responsivity of 76.2 mA/W, a large on/off current ratio of ~ 105, along with an ultra-high ultraviolet (UV)/visible rejection ratio of 1.8 × 104. More importantly, it has an ultra-fast response time of 12 µs and a remarkable specific detectivity of ~ 1013 Jones. Finally, an excellent DUV imaging capability has been identified based on the Gr/PtSe2/β-Ga2O3 Schottky junction photodetector, demonstrating its great potential application in DUV imaging systems.

Highly sensitive solar-blind deep ultraviolet photodetector based on graphene/PtSe2/β-Ga2O3 2D/3D Schottky junction with ultrafast speed

Ultrahigh Speed and Broadband Few-Layer MoTe 2 /Si 2D-3D Heterojunction-Based Photodiodes Fabricated by Pulsed Laser Deposition

Graphene has shown great potentials for new-generation photodetectors in view of its outstanding optical and electrical properties, especially its ultra-broad range absorption. Most of graphene(Gr)/Si hybrid two-dimensional(2D)-three-dimensional(3D) photodetectors, which offer a perspective on future application in integrated optoelectronics, are still however enabled the excellent detection on visible light. Herein, we reported a self-powered Gr/Si Schottky heterojunciton with a high sensivity to communication light of 1.55 μm wavelenght by using graphene film as active area. The resultant photodetectors showed a high-speed response speed up to 5.0 μs, togther with a responsivity approaching 39.5 mAW−1, which are comparable with previous graphene-based photodetectors and superior to previous Gr/Si heterojunction. The high-performance of the schottky heterojunction can be ascribed to featuring a built-in field facilitating to separate photocarriers. Combined our results with the methodology of devcie fabrication, can be utilized as pathway for large-area integration of 1.55 μm communication light photodetectors.

High responsivity and high-speed 1.55 μm infrared photodetector from self-powered graphene/Si heterojunction

Here, we demonstrate a novel 2-D–3-D graphene (Gr)/MoS2/Si nanowires Schottky-NP bipolar van der Waals heterostructure, which allows the combination of the unique properties of 2-D layered materials with the proven merits of well-developed silicon technologies. Significantly, the resultant devices exhibit an ultrahigh response speed of 17 ns with a broad spectral response characteristic, which represents most fast response for 2-D transition metal dichalcogenide (TMD)-based photodetectors and is comparable to that of commercial Si photodetectors. A high responsivity of 0.6 A $\text{W}^{-{1}}$ and a detectivity of ${8}\times {10}^{{12}}$ Jones are also achieved. This result suggests a pathway for the fabrication of high-speed photodetectors based on TMDs.

Graphene/MoS 2 /Si Nanowires Schottky-NP Bipolar van der Waals Heterojunction for Ultrafast Photodetectors

The invention discloses a Weyl semi-metal heterojunction infrared detector and preparation method thereof. According to the detector, a bottom electrode and an insulating mask layer are arranged on the upper surface of an insulating substrate in sequence; a through hole communicating with the bottom electrode is left in the center of the mask layer; two different two-dimensional semiconductor materials are deposited in sequence on the upper surface of the bottom electrode and located in the through hole, the upper layer material has Weyl semi-metal property, and in the deposition process, thetwo-dimensional semiconductor materials are deposited layer by layer and grow along a direction vertical to the bottom electrode in sequence to form a van der Waals heterojunction; and the upper sideof the mask layer is provided with a top electrode, and the bottom electrode and the lower layer semiconductor material located in the through hole form ohmic contact and the top electrode and the upper layer Weyl semi-metal material located in the through hole form ohmic contact. The detector provided by the invention is simple in preparation technology and high in repeatability, and the prepareddevice has excellent performance of wide spectral response, high sensitivity, fast response speed, easy integration and the like.

Zhijian Lu

Papers

Ultrahigh Speed and Broadband Few-Layer MoTe 2 /Si 2D-3D Heterojunction-Based Photodiodes Fabricated by Pulsed Laser Deposition

High responsivity and high-speed 1.55 μm infrared photodetector from self-powered graphene/Si heterojunction

Graphene/MoS 2 /Si Nanowires Schottky-NP Bipolar van der Waals Heterojunction for Ultrafast Photodetectors

Weyl semi-metal heterojunction infrared detector and preparation method thereof