Ultraviolet (UV) photodetectors have drawn extensive attention owing to their applications in industrial, environmental and even biological fields. Compared to UV-enhanced Si photodetectors, a new generation of wide bandgap semiconductors, such as (Al, In) GaN, diamond, and SiC, have the advantages of high responsivity, high thermal stability, robust radiation hardness and high response speed. On the other hand, one-dimensional (1D) nanostructure semiconductors with a wide bandgap, such as β-Ga2O3, GaN, ZnO, or other metal-oxide nanostructures, also show their potential for high-efficiency UV photodetection. In some cases such as flame detection, high-temperature thermally stable detectors with high performance are required. This article provides a comprehensive review on the state-of-the-art research activities in the UV photodetection field, including not only semiconductor thin films, but also 1D nanostructured materials, which are attracting more and more attention in the detection field. A special focus is given on the thermal stability of the developed devices, which is one of the key characteristics for the real applications.

Fabrication of a high-temperature deep-ultraviolet photodetector working in the solar-blind spectrum range (190-280 nm) is a challenge due to the degradation in the dark current and photoresponse properties. Herein, β-Ga2O3 multi-layered nanobelts with (l00) facet-oriented were synthesized, and were demonstrated for the first time to possess excellent mechanical, electrical properties and stability at a high temperature inside a TEM studies. As-fabricated DUV solar-blind photodetectors using (l00) facet-oriented β-Ga2O3 multi-layered nanobelts demonstrated enhanced photodetective performances, that is, high sensitivity, high signal-to-noise ratio, high spectral selectivity, high speed, and high stability, importantly, at a temperature as high as 433 K, which are comparable to other reported semiconducting nanomaterial photodetectors. In particular, the characteristics of the photoresponsivity of the β-Ga2O3 nanobelt devices include a high photoexcited current (>21 nA), an ultralow dark current (below the detection limit of 10(-14) A), a fast time response (<0.3 s), a high R(λ) (≈851 A/W), and a high EQE (~4.2 × 10(3)). The present fabricated facet-oriented β-Ga2O3 multi-layered nanobelt based devices will find practical applications in photodetectors or optical switches for high-temperature environment.

Electrochemical-coupling layer-by-layer (ECC-LbL) assembly is introduced as a novel fabrication methodology for preparing layered thin films. This method allows us to covalently immobilize functional units (e.g., porphyrin, fullerene, and fluorene) into thin films having desired thicknesses and designable sequences for both homo- and heteroassemblies while ensuring efficient layer-to-layer electronic interactions. Films were prepared using a conventional electrochemical setup by a simple and inexpensive process from which various layering sequences can be obtained, and the photovoltaic functions of a prototype p/n heterojunction device were demonstrated.

A new UV‐A photodetector based on K2Nb8O21 nanowire is successfully fabricated for the first time. The potassium niobate is synthesized using a facile molten method. The K2Nb8O21 nanowire photodetectors exhibit an excellent sensitivity and wavelength selectivity with respect to UV‐A light. Furthermore, the photodetectors show great advantages in response time compared with other sensors based on single‐oxide semiconductor nanostructures, and, especially, the responsivity is much better than that of single ZnS nanobelt photodetectors. The mechanism of conductivity is explained from the viewpoints of field emission and thermionic field emission for the change of light intensities.

We fabricate heterojunctions consisting of a single n‐type ZnO nanowire and a p‐type GaN film. The photovoltaic effect of heterojunctions exhibits open‐circuit voltages ranging from 2 to 2.7 V, and a maximum output power reaching 80 nW. Light‐emitting diodes with UV electroluminescence based on the heterojunctions are demonstrated.

A super-thin AlN layer is inserted between the intrinsic InGaN and p-InGaN in the InGaN solar cell structure to improve the photovoltaic property. The dark current is markedly decreased by more than two orders of magnitude and the short-circuit current density is increased from 0.77 mA/cm2 to 1.25 mA/cm2, leading to a doubled conversion efficiency compared to the conventional structure. Electrical transport analysis reveals that the forward electrical property is greatly improved in the range of open circuit voltage and the leakage current mechanism changes from defect related Poole-Frenkel emission to interface tunneling emission. The improvement on the electrical and photovoltaic properties is ascribed to insertion of the AlN interlayer, which not only provides a barrier to reduce tunneling for electrons, but also suppresses the nonradiative recombination.

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Electrical characteristics of leakage current paths in vertical-type n-GaN Schottky barrier diodes (SBDs) on free-standing GaN substrates are investigated by using photon emission microscopy (PEM). The PEM mapping shows that the initial failure of the SBD devices at low voltages is due to the leakage current paths from polygonal pits in the GaN epilayers. It is observed that these polygonal pits originate from carbon impurity accumulation to the dislocations with a screw-type component by microstructure analysis. For the SBD without polygonal pits, no initial failure is observed and the first leakage appeals at the edge of electrodes as a result of electric field concentration. The mechanism of leakage at pits is explained in terms of trap assisted tunneling through fitting current-voltage characteristics.