Sensing of ultraviolet light: a transition from conventional to self-powered photodetector

A 1T'-MoTe2/GaN van der Waals Schottky junction for self-powered UV imaging and optical communication

Schottky-type self-powered UV photodetectors are promising for next-generation imaging systems. Nevertheless, conventional device fabrication using high-energy metal deposition brings unintentional interface defects, leading to deteriorated device performance and inhomogeneities. Emerging two-dimensional (2D) metallic materials offer an alternative pathway to overcoming such limitations because of their naturally passivated surfaces and the ease of combining with mature bulk semiconductors via van der Waals (vdW) integration. Here, we report the controllable preparation of MoTe2 in the pure 1T' phase and the fabrication of a high-performance 1T'-MoTe2/GaN vdW Schottky photodiode. With the reduced interface states and suppressed dark current as low as 20 pA at zero bias, the photodiode exhibits a remarkable UV-to-visible (R350/R400) rejection ratio of 1.6 × 104, a stable photoresponsivity of ∼50 mA W-1 and a detectivity of 3.5 × 1012 Jones under 360 nm illumination. The photocurrent ON/OFF ratio reaches ∼4.9 × 106 under 10.5 mW irradiation (360 nm). In particular, the 1T'-MoTe2/GaN Schottky diode shows excellent weak-light detection capability, which could detect a 3 nW 360 nm laser and the light emission from a lighter with a pronounced Ilight/Idark ratio of ∼2. Finally, the applications of the device in self-powered UV imaging and optical communication are demonstrated. These results reveal the great prospects of 2D/3D integration in multifunctional optoelectronics, which may inspire novel 2D-related devices and expand their applications in widespread fields.

Self-powered photodetectors: a device engineering perspective

Nanoscale self-powered photodetectors that can work without any external source of energy are required for future applications. There is potential demand for these devices in areas like wireless surveillance, weather forecasting, remote monitoring, and places where the availability of power is scarce. This study provides an overview of state of the art research trends and improvements in self-powered photodetectors. A device engineering perspective for improvement in the figures of merit has been presented along with a description of additional effects like pyro-phototronic, piezo-phototronic, and surface plasmonics.

Self-Powered UV Photodetector Construction of the P(EDOS-TTh) Copolymer-Modified ZnO Nanoarray

To solve the problem that zinc oxide nanorods (ZnO NRs)-based self-powered ultraviolet (UV) photodetectors cannot obtain both higher responsiveness and shorter response time, P(EDOS-TTh) was prepared using 3,4-ethylenedioxyselenphene (EDOS) and terthiophene (TTh) as copolymers, which modify the ZnO NRs surface, and the ZnO/P(EDOS-TTh) P-N junction self-powered UV device is assembled. The effect of the number of electrochemical polymerization cycles on the UV photodetection performance of ZnO/P(EDOS-TTh) P-N heterojunction was studied by adjusting the number of electrochemical polymerization cycles at the monomer molar ratio of 1:1. Benefiting from the enhanced built-in electric field of the ZnO/P(EDOS-TTh) interface, balancing photogenerated carriers, and charge separation and transport. The results show that the contact between N-type ZnO NRs and P-type P(EDOS-TTh) is best when the number of polymerization cycles is 3, due to the fact that EDOS-TTh and ZnO NRs form excellent P-N heterojunctions with strong internal electric fields, and the devices show good pyroelectric effect and UV photodetection performance. Under 0 V bias and 0.32 mW/cm2 UV irradiation, the responsivity (R) of ZnO/P(EDOS-TTh) reaches 3.31 mA/W, the detectivity (D*) is 7.25 × 1010 Jones, and the response time is significantly shortened. The rise time is 0.086 s, which exhibited excellent photoelectric properties and stability. UV photodetection performance with high sensitivity and fast response time is achieved.

High-Performance Self-Powered Photoelectrochemical Ultraviolet Photodetectors Based on an In2O3 Nanocube Film

Ultraviolet photodetectors (UV PDs) have attracted significant attention due to their wide range of applications, such as underwater communication, biological analysis, and early fire warning systems. Indium oxide (In2O3) is a candidate for developing high-performance photoelectrochemical (PEC)-type UV PDs owing to its high UV absorption and good stability. However, the self-powered photoresponse of the previously reported In2O3-based PEC UV PDs is unsatisfactory. In this work, high-performance self-powered PEC UV PDs were constructed by using an In2O3 nanocube film (NCF) as a photoanode. In2O3 NCF photoanodes were synthesized on FTO by using hydrothermal methods with a calcining process. The influence of the electrolyte concentration, bias potential, and irradiation light on the photoresponse properties was systematically studied. In2O3 NCF PEC UV PDs exhibit outstanding self-powered photoresponses to 365 nm UV light with a high responsivity of 44.43 mA/W and fast response speed (20/30 ms) under zero bias potential, these results are superior to those of previously reported In2O3-based PEC UV PDs. The improved self-powered photoresponse is attributed to the higher photogenerated carrier separation efficiency and faster charge transport of the in-situ grown In2O3 NCF. In addition, these PDs exhibit excellent multicycle stability, maintaining the photocurrent at 98.69% of the initial value after 700 optical switching cycles. Therefore, our results prove the great promise of In2O3 in self-powered PEC UV PDs.

β-Ga2O3nanotube arrays for high-performance self-powered ultraviolet photoelectrochemical photodetectors

Self-powered ultraviolet (UV) photodetectors (PDs) are critical for future energy-efficient optoelectronic systems due to their low energy consumption and high sensitivity. In this paper, the vertically alignedβ-Ga2O3nanotube arrays (NTs) have been prepared on GaN/sapphire substrate by the thermal oxidation process combined with the dry etching technology, and applied in the UV photoelectrochemical photodetectors (PEC-PDs) for the first time. Based on the large specific surface area ofβ-Ga2O3NTs on GaN/sapphire substrates and the solid/liquid heterojunction, the PEC-PDs exhibit excellent self-powered characteristics under 255 nm (UVA) and 365 nm (UVC) light illumination. Under 255 nm (365 nm) light illumination, the maximum responsivity of 49.9 mA W-1(32.04 mA W-1) and a high detectivity of 1.58 × 1011Jones (1.01 × 1011Jones) were achieved for theβ-Ga2O3NTs photodetectors at 0 V bias. In addition, the device shows a fast rise/decay time of 8/4 ms (4/2 ms), which is superior to the level of the previously reported self-powered UV PEC-PDs. This high-performance PEC-PD has potential applications in next-generation low-energy UV detection systems.

Enhancing UV photodetection performance of an individual ZnO microwire p-n homojunction via interfacial engineering

As a typical broad bandgap semiconductor, ZnO has received considerable attention for developing optoelectronic devices in ultraviolet wavelengths, but suffers from a lack of high-quality single-crystalline p-type ZnO. Herein, we report the realization of a homojunction ultraviolet photodetector, which involves a p-type Sb-doped ZnO microwire (ZnO:Sb MW) and n-type ZnO layer. The p-type conductivity of the as-synthesized ZnO:Sb MWs was evidenced using an individual wire field-effect transistor. Due to its good rectifying ability and excellent photovoltaic effect, the constructed p-ZnO:Sb MW/n-ZnO homojunction is able to work as an ultraviolet photodetector in self-biased and reversely biased manners. By appropriately engineering the band alignment of the p-ZnO:Sb/n-ZnO homojunction via a MgO interface modification layer, the optimized photodetector exhibits performance-enhanced ultraviolet detection capabilities, such as the light on/off ratio reaching up to 1.6 × 10⁸, responsivity of over 267 mA W^-1 and specific detectivity of approximately 1.2 × 10¹⁴ Jones upon 365 nm light illumination at 0 V. The detector also produces faster response with rise/recovery times of 102 μs/3.6 ms. This study not only employed a novel method to synthesize genuine p-type ZnO with excellent stability and reproducibility, but also opened up substantial opportunities for developing high-performance ZnO homojunction optoelectronic devices.

MOF-Derived In2O3 Microrods for High-Performance Photoelectrochemical Ultraviolet Photodetectors

Ultraviolet photodetectors (UV PDs) have attracted extensive attention owing to their wide applications, such as optical communication, missile tracking, and fire warning. Wide-bandgap metal-oxide semiconductor materials have become the focus of high-performance UV PD development owing to their unique photoelectric properties and good stability. Compared with other wide-bandgap materials, studies on indium oxide (In₂O₃)-based photoelectrochemical (PEC) UV PDs are rare. In this work, we explore the photoresponse of In₂O₃-based PEC UV PDs for the first time. In₂O₃ microrods (MRs) were synthesized by a hydrothermal method with subsequent annealing. In₂O₃ MR PEC PDs have good UV photoresponse, showing a high responsivity of 21.19 mA/W and high specific detectivity of 2.03 × 10¹⁰ Jones, which surpass most aqueous-type PEC UV PDs. Moreover, In₂O₃ MR PEC PDs have good multicycle and long-term stability irradiated by 365 nm. Our results prove that In₂O₃ holds great promise in high-performance PEC UV PDs.

Self-powered p-CuI/n-GaN heterojunction UV photodetector based on thermal evaporated high quality CuI thin film

With vacuum thermal evaporation, the CuI film was deposited on quartz and n-GaN substrates, and the morphology, crystalline structure and optical properties of the CuI films were investigated. According to the XRD results, the CuI film preferentially grew along [111] crystal orientation on the GaN epilayer. With Au and Ni/Au ohmic contact electrodes fabricated on CuI and n-GaN, a prototype p-CuI/n-GaN heterojunction UV photodetector strong UV spectral selectivity was created. At 0 V and 360 nm front illumination (0.32 mW/cm²), the heterojunction photodetector displayed outstanding self-powered detection performance with the responsivity (R), specific detectivity (D*), and on/off ratio up to 75.5 mA/W, 1.27×10¹² Jones, and ∼2320, respectively. Meanwhile, the p-CuI/n-GaN heterojunction photodetector had excellent atmosphere stability.

Integration of H2V3O8 nanowires and a GaN thin film for self-powered UV photodetectors

H₂V₃O₈/GaN n-n heterojunction ultraviolet photodetectors are fabricated via a facile dip-coating method. The Schottky junction between the GaN and H₂V₃O₈ builds a built-in electric field to achieve the self-powered phenomenon. The photodetector presents a high photocurrent (0.23 μA) and a fast response speed (less than 0.3 s) at 0 V bias and under 365 nm light illumination (24.50 mW cm^-2). Furthermore, the photocurrent increases steadily as the light intensity increases from 0.53 to 24.50 mW cm^-2. The H₂V₃O₈/GaN heterojunction holds great potential to realize high-performance hybrid PDs.