Review of Ga2O3-based optoelectronic devices

Wide-bandgap semiconductors are expected to be applied to solid-state lighting and power devices, supporting a future energy-saving society. While GaN-based white LEDs have rapidly become widespread in the lighting industry, SiC- and GaN-based power devices have not yet achieved their popular use, like GaN-based white LEDs for lighting, despite having reached the practical phase. What are the issues to be addressed for such power devices? In addition, other wide-bandgap semiconductors such as diamond and oxides are attracting focusing interest due to their promising functions especially for power-device applications. There, however, should be many unknown phenomena and problems in their defect, surface, and interface properties, which must be addressed to fully exploit their functions. In this review, issues of wide-bandgap semiconductors to be addressed in their basic properties are examined toward their ?full bloom?.

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[Award for Best Review Paper Speech](30min.)Wide-Bandgap Semiconductor Materials: For Their Full Bloom

Electromagnetic (EM) absorbers drive the development of EM technology and advanced EM equipment. The utilization of EM energy conversion of the EM absorber to design a variety of devices is attractive and promising, especially in personal protection and healthcare. In this review article, wearable EM materials are reviewed, ranging from design strategies, EM response mechanism, EM performance improvement, to the construction of smart EM devices. For EM response mechanism, the relaxation and charge transport associated with radiation energy conversion are dissected. For wearable EM devices, two main functions are highlighted, including EM sensors to replace of human senses, as well as EM absorbers to block transmission radiation. Furthermore, the current issues and potential opportunities of the wearable EM devices are pointed out, and new directions for future prospects are proposed.

Electromagnetic absorber converting radiation for multifunction

Organic photodetectors (OPDs) have attracted continuous attention due to their outstanding advantages, such as tunability of detecting wavelength, low-cost manufacturing, compatibility with lightweight and flexible devices, as well as ease of processing. Enormous efforts on performance improvement and application of OPDs have been devoted in the past decades. In this Review, recent advances in device architectures and operation mechanisms of phototransistor, photoconductor, and photodiode based OPDs are reviewed with a focus on the strategies aiming at performance improvement. The application of OPDs in spectrally selective detection, wearable devices, and integrated optoelectronics are also discussed. Furthermore, some future prospects on the research challenges and new opportunities of OPDs are covered.

https://www.onlinelibrary.wiley.com/doi/pdf/10.1002/advs.202002418

Recent Progress in Organic Photodetectors and their Applications.

Switch type PANI/ZnO core-shell microwire heterojunction for UV photodetection

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

Patterned growth of β-Ga2O3 thin films for solar-blind deep-ultraviolet photodetectors array and optical imaging application

DOI: 10.1002/adom.201901257 flame detection, remote control, chemical and biological analysis, and secure spaceto-space communications.[3,4] In the past decade, a variety of ultrawide-bandgap (UWBG) semiconductors (e.g., ZnxMg1−xO, AlxGa1−xN, diamond, and gallium oxide (Ga2O3)) have been explored for constructing DUV photodetectors.[2–5] This class of semiconductors typically has bandgaps significantly larger than the 3.4 eV of GaN,[6] rendering them especially suitable for solar-blind DUV photodetection. Extensive studies have proven that UWBG semiconductor photodetectors can exhibit apparent advantages over traditional DUV photodetectors (e.g., photomultiplier tubes and thermal detectors), which usually have drawbacks such as being bulky and heavy, high power consumption, slow, and wavelength-independent photoresponse. Among the UWBG semiconductors, the alloys of ZnxMg1−xO and AlxGa1−xN can realize solar-blind light detection only at high Mg and Al compositions, respectively, which are inevitably accompanied with the appearance of phase segregation in ZnxMg1−xO alloy and deterioration of crystal quality in AlxGa1−xN film.[7–10] The quantum efficiency of diamond-based detectors is usually low, and their spectral response is also limited to only below 225 nm, due to the large indirect bandgap (≈5.5 eV) of diamond.[5,11] On the other hand, monoclinic Ga2O3 (β-Ga2O3), as the most stable phase of Ga2O3, has a direct wide bandgap of 4.4–5.3 eV and can be synthesized in high quality. By this token, β-Ga2O3 has proven to be excellent building block for solar-blind DUV light detection.[12–14] To date, a number of DUV photodetectors based on β-Ga2O3 in the form of either thin films or nanostructures have been successfully developed.[15–23] Benefiting from quantum confinement effect and remarkable surface/size effect, β-Ga2O3 nanostructures, in particular 1D β-Ga2O3 nanowires (NWs) or nanobelts (NBs), can exhibit attractive merits of better optical absorption, improved charge carrier transportation, and increased surface states to interact with surroundings, over their thin films’ counterpart.[3,24] Therefore, significant progresses have been made in the growth of high-quality β-Ga2O3 NWs/NBs for DUV photodetectors’ application.[25–29] For example, Feng et al. reported the synthesis of β-Ga2O3 NWs on Au-coated Si substrate by directly evaporating Ga under Photodetection in the solar-blind deep-ultraviolet (DUV) regime (200–280 nm) has received significant attention for its many critical applications in military and civil areas. In this study, a vapor–solid synthesis technique for catalyst-free growth of single-crystalline β-Ga2O3 nanowires is developed. A photodetector made of the nanowires is highly sensitive to 265 nm DUV illumination with excellent photoresponse performance. The performance parameters including Ilight/Idark ratio, responsivity, specific detectivity and response speed can attain ≈103, ≈233 A W−1, ≈8.16 × 1012 Jones, and 0.48/0.04 s, respectively. Additionally, the detector has an abrupt response cutoff wavelength at ≈290 nm with a reasonable DUV/visible (250–405 nm) rejection ratio exceeding 102. It is also found that the device can operate properly at a large applied bias of 200 V with the responsivity being enhanced to as high as ≈1680 A W−1. Moreover, such a nanowires-based photodetector can function as a DUV light image sensor with a reasonable spatial resolution. Holding the above advantages, the present DUV photodetector based on catalyst-free grown β-Ga2O3 nanowires possesses huge possibility for application in future DUV optoelectronics.

Catalyst‐Free Vapor–Solid Deposition Growth of β‐Ga2O3 Nanowires for DUV Photodetector and Image Sensor Application

https://onlinelibrary.wiley.com/doi/pdf/10.1002/adfm.201970057

Ultrawide-Bandgap Semiconductors: Recent Progress in Solar-Blind Deep-Ultraviolet Photodetectors Based on Inorganic Ultrawide Bandgap Semiconductors (Adv. Funct. Mater. 9/2019)

The invention discloses a method for growing beta-Ga2O3 nanowires without a catalyst. According to the method, a horizontal tubular furnace is adopted as a reaction device, parameters such as reactiontemperatures and gas flows are controlled, and high-quality beta-Ga2O3 nanowires are prepared through a VS (vapor solid) growth mechanism. The method is simple in process, low in cost and easy to popularize, and in addition, the obtained product is high in purity and excellent in electric and optical property.

Xing-Tong Lu

Papers

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

Patterned growth of β-Ga2O3 thin films for solar-blind deep-ultraviolet photodetectors array and optical imaging application

Catalyst‐Free Vapor–Solid Deposition Growth of β‐Ga2O3 Nanowires for DUV Photodetector and Image Sensor Application

Ultrawide-Bandgap Semiconductors: Recent Progress in Solar-Blind Deep-Ultraviolet Photodetectors Based on Inorganic Ultrawide Bandgap Semiconductors (Adv. Funct. Mater. 9/2019)

Method for growing beta-Ga2O3 nanowire without catalyst