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In this paper, a solar-blind ultraviolet photodetector (PD) based on the graphene/vertical Ga2O3 nanowire array heterojunction was proposed and demonstrated. To the best of our knowledge, it is the first time that vertical Ga2O3 nanowire arrays have been realized. Ga2O3 nanowires were obtained by thermally oxidizing GaN nanowires grown by molecular beam epitaxy on n-doped Si substrate. Then, a monolayer graphene film was transferred to Ga2O3 nanowires to form the graphene/vertical Ga2O3 nanowire array heterojunction and transparent electrodes. The fabricated device exhibited a responsivity (R) of 0.185 A/W and rejection ratio (R258 nm/R365 nm) of 3×104 at the bias of −5 V. Moreover, the fast response times of this PD were 9 and 8 ms for the rise and decay times under 254 nm illumination, respectively, which are attributed to the unique properties of nanowire arrays and the graphene/vertical Ga2O3 nanowire array heterojunction structure.

Due to the wide application of UV-A (320 nm–400 nm) and UV-C (200 nm–280 nm) photodetectors, dual-wavelength (UV-A/UV-C) photodetectors are promising for future markets. A dual-wavelength UV photodetector based on vertical (Al,Ga)N nanowires and graphene has been demonstrated successfully, in which graphene is used as a transparent electrode. Both UV-A and UV-C responses can be clearly detected by the device, and the rejection ratio (R254 nm/R450 nm) exceeds 35 times at an applied bias of –2 V. The short response time of the device is less than 20 ms. Furthermore, the underlying mechanism of double ultraviolet responses has also been analyzed systematically. The dual-wavelength detections could mainly result from the appropriate ratio of the thicknesses and the enough energy band difference of (Al,Ga)N and GaN sections. [ABSTRACT FROM AUTHOR]

As the key device in a UV warning system, a solid‐state UV photodetector has attracted great attention. Herein, a new UV photodetector structure based on vertical (Al, Ga)N nanowires with graphene electrode and Si substrate is designed and demonstrated. By graphene/vertical (Al, Ga)N nanowire array heterojunction, the rectifying characteristics of I–V curve are formed, and the dark current is 54 nA at −2 V bias. The fabricated device exhibits a responsivity of 0.176 mA W−1 at the bias of −2 V, as well as a stable switching characteristic. It is proposed that the photogenerated electrons and holes can reach positive and negative electrodes by diffusion or tunneling effect, even with thick AlN sections. This method can promote the implementation of low cost for UV photodetector with adjustable detection range nowadays. [ABSTRACT FROM AUTHOR]

In this paper, a solar-blind ultraviolet photodetector (PD) based on the graphene/vertical Ga2O3 nanowire array heterojunction was proposed and demonstrated. To the best of our knowledge, it is the first time that vertical Ga2O3 nanowire arrays have been realized. Ga2O3 nanowires were obtained by thermally oxidizing GaN nanowires grown by molecular beam epitaxy on n-doped Si substrate. Then, a monolayer graphene film was transferred to Ga2O3 nanowires to form the graphene/vertical Ga2O3 nanowire array heterojunction and transparent electrodes. The fabricated device exhibited a responsivity (R) of 0.185 A/W and rejection ratio (R258 nm/R365 nm) of 3×104 at the bias of −5 V. Moreover, the fast response times of this PD were 9 and 8 ms for the rise and decay times under 254 nm illumination, respectively, which are attributed to the unique properties of nanowire arrays and the graphene/vertical Ga2O3 nanowire array heterojunction structure. [ABSTRACT FROM AUTHOR]

Broadband ultraviolet (BUV) photodetectors responding to the multiband spectrum can effectively reduce false alarm rates and improve the accuracy and versatility of detection systems in various situations. A high‐responsivity BUV photodetector based on vertical Ga2O3/GaN nanowire array is proposed and demonstrated. Ga2O3/GaN nanowires are obtained by partially thermally oxidizing GaN nanowires grown by molecular beam epitaxy and used to combine with a monolayer graphene film to form graphene/Ga2O3/GaN heterojunction. Moreover, the oxidation mechanism of GaN nanowires is further investigated by the developed thermal oxidation model. The fabricated devices exhibit excellent performance with a broadband spectral response of exceeding 550 A W−1 at −5 V and a fast‐response speed in the millisecond range, which can be attributed to the optical properties of vertical nanowire array structure and the internal gain mechanism of graphene/Ga2O3/GaN heterojunction. A high‐responsivity broadband ultraviolet photodetector based on vertical Ga2O3/GaN nanowire array is proposed and demonstrated. The nanowires are obtained by partial thermal oxidation and form a graphene/Ga2O3/GaN heterojunction. The fabricated devices exhibit a great broadband spectral response with the high responsivity exceeding 550 A W−1. Meanwhile, an oxidation model is proposed to explain the crystalline transformation of GaN nanowires in thermal oxidation. [ABSTRACT FROM AUTHOR]

In the electrodes of spent lithium-ion batteries, graphite, due to its layered structure and crystalline composition, presents significant recyclable value, yet it has not been fully utilized. This study proposes a modified mechanical exfoliation method (MEM), which employs leaching-drying pretreatment to transform waste graphite into two-dimensional graphene. Three drying methods were evaluated, among which freeze drying was found to be the most conducive for exfoliation. Pneumatic drying, being basic and simple, did not exhibit any special effects that benefit exfoliation. XRD results showed that leaching restores the lamellar structure of graphite, with peak intensity (× 105) increasing from 6.5 to 8.9–10.1. XPS analysis revealed that vacuum roasting drying leads to dehydration condensation of hydroxyl groups between layers, resulting in the obtained graphite having the best dehydration effect and the lowest oxygen content, at only 1.89%, but this enhances interlayer forces, which is counterproductive for exfoliation. In contrast, freeze drying, through the volumetric expansion caused by the freezing of water, disrupts the interlayer forces, achieving an interlayer spacing of 337.5 nm, which facilitates the exfoliation of graphene. This was confirmed by TEM results. This method effectively overcomes the problem of impurity contamination in waste graphite, providing a new approach for the high-value utilization and green recycling of graphite in spent lithium batteries. [Display omitted] • Dehydration condensation of vacuum drying results in a tighter graphite layer. • Volume expansion from water freezing can break the interlayer force of graphite. • The modified MEM can remove impurities and avoid secondary contamination. • Graphite wastes in spent LIBs can be environmentally upcycled into 2D graphene. [ABSTRACT FROM AUTHOR]