Dual-wavelength visible photodetector based on vertical (In,Ga)N nanowires grown by molecular beam epitaxy

Flexible bidirectional self-powered photodetector with significantly reduced volume and accelerated response speed based on hydrogel and lift-off GaN-based nanowires

Due to the wide range of potential applications for next-generation multi-functional devices, the flexible self-powered photodetector (PD) with polarity-switchable behavior is essential but very challenging to be realized. Herein, a wearable bidirectional self-powered PD based on detached (Al,Ga)N and (In,Ga)N nanowires has been proposed and demonstrated successfully. Arising from the photovoltage-competing dynamics across (Al,Ga)N and (In,Ga)N nanowire photoelectrodes, such PD can generate the positive (33.3 mA W -1) and negative (-0.019 mA W -1) photo-responsivity under ultraviolet (UV) and visible illumination, respectively, leading to the bidirectional photocurrent behavior. Thanks to the introduction of quasi solid-state hydrogel, the PD can work without the liquid-electrolyte, thus remarkably reducing the volume from about 482 cm3 to only 0.18 cm3. Furthermore, the use of hydrogel is found to enhance response speed in the UV range by reducing the response time for more than 95%, which is mainly attributed to the increased open circuit potential and reduced ion transport distance. As the GaN connecting segment is pretty thin, the piezoelectric charges generated by stress are proposed to have only a limited effect on the photocurrent density. Therefore, both the stable on-off switching characteristics and photocurrent densities can still be achieved after being bent 400 times. With an excellent flexibility, this work creates opportunities for technological applications of bidirectional photocurrent PDs in flexible optoelectronic devices, e.g., wearable intelligent sensors.

Engineering GaN/AuNC core-shell nanowire heterojunctions by gold nanoclusters with excitation-dependent behavior for enhancing the responsivity and stability of self-driven photodetectors

Self-driven broadband photodetectors (PDs) with low-power consumption have great potential applications in the wide range of next-generation optoelectronic devices. In this study, a self-driven broadband PD responding to an ultraviolet-visible range based on gallium nitride/gold nanocluster (GaN/AuNC) core-shell nanowire heterojunctions is fabricated for the first time. By introducing the AuNCs onto the GaN nanowire surfaces, the GaN/AuNC core-shell nanowire heterojunctions can be formed efficiently. It is crucial that AuNCs have the functions of light collectors and hole conductors in heterojunctions due to the suitable energy level alignment. Under the optimized conditions of AuNCs, it is found that GaN/AuNC core-shell nanowires can significantly increase the photocurrent and responsivity of PDs, mainly resulting from the light interreflection within the heterojunctions and the effective improvement of carrier transport. Owing to the excitation-dependent emission behavior of AuNCs, the responsivity of PD with GaN/AuNC core-shell nanowire heterojunctions can be enhanced by around 330% compared with that of PD without AuNCs under visible illumination. Furthermore, GaN/AuNC hybrid nanowires with excitation-dependent fluorescence behavior can modulate the enhanced amplitude performance of broadband PDs. Owing to the high stability of AuNCs, the photocurrent of the PD with AuNCs is still quite stable after continuous operation for more than 20 000 s. Therefore, this study provides an effective method for developing new broadband PDs with high performance and low energy consumption.

Developing low-cost nanohybrids of ZnO nanorods and multi-shaped silver nanoparticles for broadband photodetectors

Photodetectors are essential elements for various applications like fiber optic communication systems, biomedical imaging, and so on. Thus, improving the performance and reducing the material costs of photodetectors would act as a motivation toward the future advancement of those applications. This study introduces the development of a nanohybrid of zinc oxide nanorods (ZnONRs) and multi-shaped silver nanoparticles MAgNPs through a simple solution process; in which ZnONRs are hybridized with MAgNPs to enable visible absorption through the surface plasmon resonance (SPR) effect. The photodetector based on ZnONRs/MAgNPs is responsive to visible light with representative wavelengths of 395, 464, 532 and 640 nm, and it exhibits high responsivity (R), photoconductive gain (G) and detectivity (D). The maximum R is calculated from the fitting curve of the responsivity-power relation with the value of 5.35 × 10³ (mA W^-1) at 395 nm excitation. The highest G and D reach 8.984 and 3.71 × 10¹⁰ Jones at that wavelength. This reveals the promise of our innovative broadband photodetector for practical usage.

Self-powered (In,Ga)N-nanowire-based photodetector with fast response speed for under-seawater detection

Due to the requirements of oceanography exploration and detection, self-powered photodetectors (PDs) with low-power consumption are essential for the next-generation optoelectronic applications. In this work, we successfully demonstrate a self-powered photoelectrochemical (PEC) PD in seawater based on the (In,Ga)N/GaN core-shell heterojunction nanowires. Compared to those of the PD in pure water, it is found that the upward and downward overshooting features of current can be the key reason contributing to the much faster response speed of the PD in seawater. Thanks to the enhanced response speed, the rise time of PD can be reduced more than 80%, and the fall time remains only 30% by applying in seawater instead of pure water. The key factors of generating these overshooting features should be the instantaneous temperature gradient, carrier accumulation and elimination on the semiconductor/electrolyte interfaces at the moments of light on and off. By the analysis of experimental results, the Na⁺ and Cl^- ions are proposed to be the main factors affecting the PD behavior in seawater, which can enhance the conductivity and accelerate the oxidation-reduction reaction significantly. This work paves an effective way to develop the new self-powered PDs for the wide applications in under-seawater detection and communication.

A Self-Powered Transparent Photodetector Based on Detached Vertical (In,Ga)N Nanowires with 360° Omnidirectional Detection for Underwater Wireless Optical Communication

Underwater wireless optical communication (UWOC) is a wireless communication technology using visible light to transmit data in an underwater environment, which has wide applications. Based on lift-off (In,Ga)N nanowires, this work has proposed and successfully demonstrated a self-powered photoelectrochemical (PEC) photodetector (PD) with excellent transmissivity. The transparent functionality of the PD is critical for 360° omnidirectional underwater detection, which was realized by detaching the (In,Ga)N nanowires from the opaque epitaxial substrates to the indium tin oxide (ITO)/glass. It was also found that the insulating SiO2 layer can enhance the photocurrent by about 12 times. The core-shell structure of the nanowires is beneficial for generating carriers and contributing to the photocurrent. Furthermore, a communication system with ASCII code is set to demonstrate the PD detection in underwater communication. This work paves an effective way to develop 360° omnidirectional PDs for the wide applications in UWOC system and underwater photodetection.