Oxygen vacancy (O-V) states are the most prevalent chemical defects in metal oxides without extrinsic dopants, which govern the regime of photoelectrochemical (PEC) kinetics. So far, although tremendous strategies are developed to overcome the negative effects from O-V, the threshold at which O-V plays a positive role has not been specifically studied. Furthermore, the kinetics of stoichiometry changes as well as their effects on the charge transport aroused from manipulating O-V distribution are still in confusion. Here, taking alpha-Ga2O3 nanorod arrays as the model, we show the evolution mechanism about the changes in O-V distribution during vacancy engineering. Since the O diffusion flow into bulk is regulated by the surface O-V-assisted migration mechanism, the surface O-V concentration decreased first and recovered slightly after a period of time. This is deviated from the common sense that the longtime O-2 annealing should bring about monotonical O-V decrease at the surface. After PEC characterization and theory calculation, the results show that O-V plays to the score in the PEC process, depending on its own spatial distribution. The optimized engineering strategy of O-V spatial distribution is proposed to establish the efficient carrier separation nanoarchitectures for high-performance UV photodetection. This work provides an insight for clarifying fundamental rules for defect engineering in the PEC field.

In this study, α-Ga2O3 nanorod arrays (NRAs) were grown using a simple and low-cost two-step hydrothermal method. Subsequently, a photoelectrochemical ultraviolet photodetector (PEC-UV PD) based on the α-Ga2O3 NRAs was fabricated, which can operate at zero bias and has a performance far superior to that of PEC-UV PDs based on the one-step hydrothermal method. Under 2 mW/cm2 illumination at 254 nm, the device achieved a responsivity of 26.59 mA/W, an external quantum efficiency of 12.98

High-efficiency hydrogen production through photoelectrochemical (PEC) water splitting has emerged as a promising solution to address current global energy challenges. III-nitride semiconductor photoelectrodes with nanostructures have demonstrated great potential in the near future due to their high light absorption, tunable direct band gap, and strong physicochemical stability. However, several issues, including surface trapping centers, surface Fermi level pinning, and surface band bending, need to be addressed. In this work, enhanced photovoltaic properties have been achieved using gallium nitride (GaN) nanowires (NWs) photoelectrodes by adopting an alkaline solution surface treatment method to reduce the surface states. It was found that surface oxides on NWs can be removed by an alkaline solution treatment without changing the surface morphology through X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and other characterization methods. These findings provide new insights to the development of high-efficiency photoelectrodes for new energy source applications.

Realizing energy-efficient devices with sustainable and independent operation is a large challenge for next-generation photodetection systems in various environments. In this study, we present a high-response and fast-speed ultraviolet photodetector (UV PD) based on the p-AlGaN/AlN/n-GaN nanowires (NWs) heterojunction, which could operate at a 0 V bias for underwater photodetection through the photoelectrochemical (PEC) process. Compared to the UV PD without AlN insertion, the detection performance would be increased to 3-5 times for underwater solar-blind UV detection under the effect of heterostructure band engineering to prevent carrier drift and recombination at 0 V bias under 255 nm illumination. Furthermore, the photoresponsivity and response speed can be further improved by a surface modification strategy to adjust the carrier transport between the nitride semiconductor and electrolyte. These promising results lay a solid foundation for the development of III-nitride high-efficiency, self-powered PEC photosynthesis devices in the future.

The optical chirality of metamaterials gives birth to distinct responses of left circularly polarized (LCP) and right circularly polarized (RCP) light, leading to asymmetric transmission and circular dichroism (CD) of circularly polarized light. In this work, meta-atom structure composed of square and semicircular combinations were designed, which exhibits extreme high ratio of transmission, reflection and CD values in blue light range. In compare to other reported structures, the structure composed of semicircular and square combinations can achieve better asymmetric transmission. At the wavelength of 460 nm, the incident LCP light can be mostly converted to RCP light, and the incident RCP light can be almost completely reflected. Furthermore, the geometric phase can be controlled by designing the orientation angle of the meta-atom, and the metamaterial can function under any linear or circular polarization and achieving the regulation of the light field. The designed metamaterial provides promising insights into the high CD and possible applications in optical integrated devices, such as anomalously refracted, focusing, and holograms, etc.

An ultraviolet-infrared (UV-IR) dual-wavelength photodetector (PD) based on a monolayer (ML) graphene/GaN heterostructure has been successfully fabricated in this work. The ML graphene was synthesized by chemical vapor deposition (CVD) and subsequently transferred onto GaN substrate using polymethylmethacrylate (PMMA). The morphological and optical properties of the as-prepared graphene and GaN were presented. The fabricated PD based on the graphene/GaN heterostructure exhibited excellent rectify behavior by measuring the current–voltage (I–V) characteristics under dark conditions, and the spectral response demonstrated that the device revealed an UV-IR dual-wavelength photoresponse. In addition, the energy band structure and absorption properties of the ML graphene/GaN heterostructure were theoretically investigated based on density functional theory (DFT) to explore the underlying physical mechanism of the two-dimensional (2D)/three-dimensional (3D) hybrid heterostructure PD device. This work paves the way for the development of innovative GaN-based dual-wavelength optoelectronic devices, offering a potential strategy for future applications in the field of advanced photodetection technology.

Flexible electronic devices have great application potential in the field of next-generation consumer electronics. In this paper, we have demonstrated that applying external bending on AlGaN-based flexible deep-ultraviolet light-emitting diodes (DUV LEDs) can modulate the electrical characteristics of the quantum-well heterostructures. The internal quantum efficiency of DUV LEDs can be significantly improved by applying external strain on the device in bend-up mode. In addition, the peak emission of the DUV LEDs can be significantly tuned by bending the device into concave or convex curvatures. This desirable feature allows a single device to be applied in different environments and fields by applying external strain.