Solar-powered water evaporation — the extraction of vapour from liquid water using solar energy — provides the basis for the development of eco-friendly and cost-effective freshwater production. Liquid water consumes and carries energy, and, thus, plays an essential role in this process. As such, extensive experimental and theoretical studies have been focused on water management to achieve efficient solar vapour generation. Many innovative materials have been proposed to enable highly controllable and efficient solar-to-thermal energy conversion to address the challenges in the energy–water nexus from the microscale to the molecular level. In this Review, we summarize the fundamental principles of materials design for efficient solar-to-thermal energy conversion and vapour generation. We discuss how to integrate photothermal materials, nanostructures/microstructures and water–material interactions to improve the performance of the evaporation system via in situ utilization of solar energy. Focusing on materials science and engineering, we overview the key challenges and opportunities for nanostructured and microstructured materials in both fundamental research and practical water-purification applications. Materials engineering enables the control of water–material interactions in solar vapour generators, which aim to efficiently utilize solar energy for the cost-effective production of clean water. This Review discusses material-design principles for solar evaporators, spanning from macrostructures to molecular configurations.

Materials for solar-powered water evaporation

Ultraviolet (UV) radiation has a variety of impacts including the health of humans, the production of crops, and the lifetime of buildings. Based on the photovoltaic effect, self-powered UV photode...

Self-Powered Ultraviolet Photodetector with Superhigh Photoresponsivity (3.05 A/W) Based on the GaN/Sn:Ga2O3 pn Junction.

Due to its significant applications in many relevant fields, light detection in the solar-blind deep-ultraviolet (DUV) wavelength region is a subject of great interest for both scientific and industrial communities. The rapid advances in preparing high-quality ultrawide-bandgap (UWBG) semiconductors have enabled the realization of various high-performance DUV photodetectors (DUVPDs) with different geometries, which provide an avenue for circumventing numerous disadvantages in traditional DUV detectors. This article presents a comprehensive review of the applications of inorganic UWBG semiconductors for solar-blind DUV light detection in the past several decades. Different kinds of DUVPDs, which are based on varied UWBG semiconductors including Ga2O3, MgxZn1−xO, III-nitride compounds (AlxGa1−xN/AlN and BN), diamond, etc., and operate on different working principles, are introduced and discussed systematically. Some emerging techniques to optimize device performance are addressed as well. Finally, the existing techniques are summarized and future challenges are proposed in order to shed light on development in this critical research field.

Recent Progress in Solar-Blind Deep-Ultraviolet Photodetectors Based on Inorganic Ultrawide Bandgap Semiconductors

Solar-blind photodetectors are of great interest to a wide range of industrial, civil, environmental, and biological applications. As one of the emerging ultrawide-bandgap semiconductors, gallium oxide (Ga2O3) exhibits unique advantages over other wide-bandgap semiconductors, especially in developing high-performance solar-blind photodetectors. This paper comprehensively reviews the latest progresses of solar-blind photodetectors based on Ga2O3 materials in various forms of bulk single crystal, epitaxial films, nanostructures, and their ternary alloys. The basic working principles of photodetectors and the fundamental properties and synthesis of Ga2O3, as well as device processing developments, have been briefly summarized. A special focus is to address the physical mechanism for commonly observed huge photoconductive gains. Benefitting from the rapid development in material epitaxy and device processes, Ga2O3-based solar-blind detectors represent to date one of the most prospective solutions for UV detection technology towards versatile applications.

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Review of gallium-oxide-based solar-blind ultraviolet photodetectors

In recent years, solar-blind ultraviolet (UV) photodetectors have attracted significant attention from researchers in the field of semiconductor devices due to their indispensable properties in the fields of high-temperature event monitoring, anti-terrorism, security and ad hoc network communication. As an important member of the third-generation semiconductors, β-Ga2O3 is considered to be one of the most promising candidates for solar-blind UV detectors due to its ultra-wide band gap (∼4.9 eV), economic efficiency, high radiation resistance and excellent chemical and thermal stability. Herein, we provide a comprehensive review on Ga2O3-based solar-blind UV photodetectors, with a detailed introduction of the developmental process of material growth methods and device manufacturing in the past decade. We classify the currently reported Ga2O3-based solar-blind UV photodetectors (mainly including photoconductive detectors, heterogeneous PN junction detectors and Schottky junction detectors) and summarize their respective superiorities and potentials for improvement. Finally, considering the actual application requirements, we put forward some meaningful suggestions, including energy band engineering and homogeneous epitaxy, for the future development of Ga2O3 material growth and device manufacturing.

Gallium oxide solar-blind ultraviolet photodetectors: a review

The metastable α-phase Ga2O3 is an emerging material for developing solar-blind photodetectors and power electronic devices toward civil and military applications. Despite its superior physical properties, the high quality epitaxy of metastable phase α-Ga2O3 remains challenging. To this end, single crystalline α-Ga2O3 epilayers are achieved on nonpolar ZnO (1120) substrates for the first time and a high performance Au/α-Ga2O3/ZnO isotype heterostructure-based Schottky barrier avalanche diode is demonstrated. The device exhibits self-powered functions with a dark current lower than 1 pA, a UV/visible rejection ratio of 103 and a detectivity of 9.66 × 1012 cm Hz1/2 W–1. Dual responsivity bands with cutoff wavelengths at 255 and 375 nm are observed with their peak responsivities of 0.50 and 0.071 A W–1 at −5 V, respectively. High photoconductive gain at low bias is governed by a barrier lowing effect at the Au/Ga2O3 and Ga2O3/ZnO heterointerfaces. The device also allows avalanche multiplication processes in...

Solar-blind Photodetector with High Avalanche Gains and Bias-tunable Detecting Functionality Based on Metastable Phase α-Ga2O3/ZnO Isotype Heterostructures

Carbonized Bamboos as Excellent 3D Solar Vapor-Generation Devices

In this letter, the high-temperature performance of 4H-SiC avalanche photodiodes (APDs) working in Geiger mode is studied for the first time. At unity gain bias, the maximum quantum efficiency of the APD increases from 53.4% at 290 nm to 63.3% at 295 nm as temperature rises from room temperature to 150 °C. Meanwhile, the dark current of the APD before breakdown increases by more than two to three orders of magnitude. At a fixed gain of 1.3 × 106, the single photon counting efficiency at 280 nm only slightly drops from 6.17% to 6% in the same temperature range, whereas the dark count rate increases from 22 to 80 KHz. This letter indicates that SiC APDs have the potential to work in a high-temperature harsh environment with single photon counting capability.

High-Temperature Single Photon Detection Performance of 4H-SiC Avalanche Photodiodes

In this paper, carrier transport and gain mechanisms are exploited in the $\beta $ -Ga2O3-based metal–semiconductor–metal photodetectors with Au back-to-back Schottky contacts. The resultant devices exhibit a low dark current of $10^{{3}}$ , and a photo-to-dark current ratio of 50 at 473 K, indicative of its strong operation capability at high temperature and in harsh environments. Temperature-dependent current–voltage features reveal that the dark reverse leakage is dominated by the thermionic field emission at low electric field and Poole–Frenkel emission from a deep trap level of 0.42 eV under the conduction band at high field, respectively. These negatively charged traps positioned below the Fermi level in the vicinity of Schottky interface capture photogenerated holes and reduce the barrier height upon illumination. The temperature- and bias-dependent photoresponse features are identified in physics that the photoconductive gain as well as slow response speed is originated from the change of barrier height due to trap repopulation.

Carrier Transport and Gain Mechanisms in $\beta$ –Ga 2 O 3 -Based Metal–Semiconductor–Metal Solar-Blind Schottky Photodetectors

In this letter, we report a quasi-vertical GaN junction barrier Schottky diode on low-cost sapphire substrate. With the high quality GaN epitaxy and selective-area p-islands formed via Magnesium ion implantation at the anode region, reverse leakage in level of 10−7 A/cm2 was achieved, as well as a high on/off current ratio of 1010 and a high breakdown voltage of 838 V. Meanwhile, advantageous characteristics as expected in vertical GaN Schottky barrier diode were realized, including a low turn-on voltage of 0.5 V and fast switching performance under 400 V/10 A operation condition. Along with the improved heat dissipation via substrate thinning and packaging techniques, the diode retains a relatively low thermal resistance, enabling high current rectification level over 60 A, power efficiency up to 98.7 %, while maintaining low case temperatures.

Dong Zhou

Papers

Solar-blind Photodetector with High Avalanche Gains and Bias-tunable Detecting Functionality Based on Metastable Phase α-Ga2O3/ZnO Isotype Heterostructures

Carbonized Bamboos as Excellent 3D Solar Vapor-Generation Devices

High-Temperature Single Photon Detection Performance of 4H-SiC Avalanche Photodiodes

Carrier Transport and Gain Mechanisms in $\beta$ –Ga 2 O 3 -Based Metal–Semiconductor–Metal Solar-Blind Schottky Photodetectors

High-Voltage Quasi-Vertical GaN Junction Barrier Schottky Diode With Fast Switching Characteristics