Solar-blind UV Research Articles

Enhanced performance of high Al-content AlGaN MSM photodetectors by electrode modification using hexadecanethiol.

A metal electrode modification process for AlGaN-based metal-semiconductor-metal (MSM) photodetectors have been introduced to enhance the response of solar-blind ultraviolet (UV) light detection. The hexadecanethiol organic molecules are chemically adsorbed on the electrodes of high-Al-content Al0.6Ga0.4N MSM solar-blind UV photodetectors, which can reduce the work function of the metal electrode and change the height of the Schottky barrier. This modification process significantly increases the photocurrent and responsivity of the device compared with the referential photodetector without modification. Additionally, the adverse effects caused by the surface state and polarization of the AlGaN materials are effectively reduced, which can be beneficial for improving the electrical performances of III-nitride-based UV photodetectors.

High-Responsivity Solar-Blind Ultraviolet Photodetectors Based on Carbon Nanodots/Graphene Hybrids

The intrinsically poor optical absorption and short carrier lifetime of graphene have restricted its practical application in photodetectors. Carbon nanodots (CNDs) have received much attention due to their fascinating optical properties, environmentally friendly nature, small size, and superiority of a large optical absorptivity. Thus, in this article, a hybrid photodetector based on CNDs and graphene has been proposed for the solar-blind ultraviolet (UV) photodetection, in which CNDs were integrated with graphene to form a hybrid structure which was capable of detecting UV light with 254 nm. Here, this article also demonstrated that a high photoresponsivity of ~433.33 A/W and a detectivity of ~1.08 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> Jones can be obtained in the hybrid photodetector. UV illumination causes photogenerated electrons and holes in CNDs. Holes transfer to graphene and then recirculate many times, which originates from the high carrier mobility of graphene and the prolonged lifetime of excited electrons that remain trapped in CNDs. Our result demonstrates that the integration of graphene and CNDs shows better optical absorption and wavelength selectivity. Together with the mechanism, it paves a step for practical applications of quantum dots sensitized graphene-based photodetectors.

Indium Gallium Oxide Alloys: Electronic Structure, Optical Gap, Surface Space Charge, and Chemical Trends within Common-Cation Semiconductors.

The electronic and optical properties of (InxGa1-x)2O3 alloys are highly tunable, giving rise to a myriad of applications including transparent conductors, transparent electronics, and solar-blind ultraviolet photodetectors. Here, we investigate these properties for a high quality pulsed laser deposited film which possesses a lateral cation composition gradient (0.01 ≤ x ≤ 0.82) and three crystallographic phases (monoclinic, hexagonal, and bixbyite). The optical gaps over this composition range are determined, and only a weak optical gap bowing is found (b = 0.36 eV). The valence band edge evolution along with the change in the fundamental band gap over the composition gradient enables the surface space-charge properties to be probed. This is an important property when considering metal contact formation and heterojunctions for devices. A transition from surface electron accumulation to depletion occurs at x ∼ 0.35 as the film goes from the bixbyite In2O3 phase to the monoclinic β-Ga2O3 phase. The electronic structure of the different phases is investigated by using density functional theory calculations and compared to the valence band X-ray photoemission spectra. Finally, the properties of these alloys, such as the n-type dopability of In2O3 and use of Ga2O3 as a solar-blind UV detector, are understood with respect to other common-cation compound semiconductors in terms of simple chemical trends of the band edge positions and the hydrostatic volume deformation potential.

Reinforcement of double built-in electric fields in spiro-MeOTAD/Ga2O3/Si p–i–n structure for a high-sensitivity solar-blind UV photovoltaic detector

The spiro-MeOTAD/Ga2O3/Si p–i–n structure was developed for a high-sensitivity solar-blind UV photodetector.

Theoretical study on photoemission of two-dimensional variable-Al composition AlxGa1-xN nanorod array photocathode

With the development of the application of sun-blind ultraviolet (UV) detectors, the research of photoelectric detection devices with high-efficiency solar blind detection performance has become a hot spot. Therefore, in order to meet this demand, we have studied AlxGa1-xN photocathode with dielectric wavelength tunable properties. Since the actual measured quantum efficiency is too different from the simulation calculation results, in order to solve the secondary absorption problem of the nanorod array photocathode, we propose to use a variable-Al composition AlxGa1-xN nanorod array structure as a solution. By establishing a two-dimensional photoemission model of AlxGa1-xN nanorod array photocathode with variable-Al composition, the effect of the built-in electric field generated by variable-Al composition on the top surface quantum efficiency of nanorods was analyzed. A variable-Al composition AlxGa1-xN nanorod array photocathode structure with excellent solar blind response characteristics was obtained. Therefore, the research in this paper can provide some theoretical references for the manufacture of vacuum solar blind UV detectors with high efficiency detection performance.

In situ and tunable structuring of semiconductor-in-glass transparent composite.

SummarySemiconductor-in-glass composites are an exciting class of photonic materials for various fundamental applications. The significant challenge is the scalable elaboration of composite with the desirable combination of tunable structure, high semiconductor loading ratio, and excellent transparency. Here we report that the topological engineering strategy via hybridization of the glass network former enables to surmount the aforementioned challenge. It not only facilitates the in situ precipitation of (Ga2-xAlx)O3 domains with continuously tunable composition but also allows to simultaneously refine the grain size and enhance the crystallinity. In addition, the composites exhibit excellent transparency and can host various active dopants. We demonstrate the attractive broadband optical response of the composite and achieve the pulse laser operation in mid-infrared waveband. The findings are expected to provide a fundamental principle of in situ modification in hybrid system for generation of high-performance semiconductor-in-glass composites.

Performance analysis of MIMO communication system with NLOS UV channel

Performance analysis is carried out, of a multiple input, multiple output (MIMO) ultraviolet (UV) communication system with a non-line-of-sight (NLOS) UV channel. The achievable bit error coefficient is calculated using three spatial multiplexing methods for different bitrate values, azimuthal deviation between the directional diagrams of an optical transmitter and an optical receiver, and different noise levels. Full Text: PDF ReferencesZ. Xu, B. Sadler, "Ultraviolet communications: potential and state-of-the-art", IEEE Commun. Mag. 4667-73 (2009). CrossRef D. Han, Y. Liu, K. Zhang et al., "Theoretical and experimental research on diversity reception technology in NLOS UV communication system", Opt. Expr. 20(14), 15833 (2012). CrossRef Q. Guo, N. He, Z. He, "Research on the channel performances and transmission in UV-LED scatter communications", Study Opt. Comm. 3, 64 (2013). DirectLink G. Chen, L. Liao, Z. Li et al., "Experimental and simulated evaluation of long distance NLOS UV communication", Communication Systems, Networks and Digital Signal Processing (CSND-SP), 9th Int. Symp. on IEEE, 904-909 (2014). CrossRef M.A. El-Shimy, S. Hranilovic, "Spatial-Diversity Imaging Receivers for Non-Line-of-Sight Solar-Blind UV Communications", J. Lightwave Techn. 33(11), 2246 (2015). CrossRef G. Shaw, M. Nischan, M. Iyengar, S. Kaushik, M. Griffin, NLOS UV communication for distributed sensor systems, Proc. SPIE 412683, 96 (2000). CrossRef I.S. Konstantinov, G.S. Vasyliev, O.R. Kuzichkin, D.I. Surzhik, I.A. Kurilov, S.A. Lazarev, "AUV Link Mobile Ad-Hoc Network Examination", J. Eng. Adv. Techn. 8(5S) July 2019 CrossRef I.S. Konstantinov, G.S. Vasilyev, O.R. Kuzichkin, I.A. Kurilov, S.A. Lazarev, "Modeling and Analysis of the Characteristics of Ultraviolet Channels under Different Conditions of Radiation Propagation for the Organization of Wireless AD-HOC Network", J. Adv. Res. Dynam. Contr. Syst. 07, 1853 (2018) DirectLink I.S. Konstantinov, G.S. Vasyliev, O.R. Kuzichkin, D.I. Surzhik, I.A. Kurilov, S.A. Lazarev, "Development Of Uv Communication Channels Characteristics Modeling Algorithm In A Mobile Ad-Hoc Network", J. Adv. Res. Dynam. Contr. Syst. 11(08), 1920 (2019). CrossRef G. Chen, F. Abou-Galala, Z. Xu, B.M. Sadler, "Experimental evaluation of LED-based solar blind NLOS communication links", Opt. Expr. 16(19), 15059 (2008). CrossRef

The growth of HVPE α-Ga2O3 crystals and its solar-blind UV photodetector applications

While Ga2O3 crystals are considered as the next generation optoelectronic materials, the exploration of HVPE α-Ga2O3 crystals and their use as solar-blind UV photodetector are still insufficient. In this paper, we investigated the structural characterization of HVPE α-Ga2O3 materials and their properties as solar-blind photodetector. HVPE α-Ga2O3 exhibited excellent structural properties with relatively good crystallinity, and smooth surface morphology, without any complicated process. Raman investigations confirmed the existence of slight compressive strain in the as-grown HVPE α-Ga2O3. UV–visible spectrophotometry proved that HVPE α-Ga2O3 had an optical bandgap of 5.15 eV, evidencing the suitability of this material for application as solar-blind photodetector. Furthermore, the photodetector synthesized using HVPE α-Ga2O3 showed excellent photo-response characteristics. We believe that this study will support further development of functional oxide semiconductor materials and opto-electronic devices.

Low-temperature processed high-performance visible–transparent Ga2O3 solar blind ultraviolet photodetectors with the indium–tin–oxide electrode

High-performance visible–transparent electronics are being used as emerging technologies in next-generation ‘see-through’ devices. In this work, the high-performance fully visible–transparent metal–semiconductor-metal (MSM) interdigitated Ga2O3 solar blind ultraviolet (UV) photodetector (PD) was successfully fabricated by using the ITO electrode. The Ga2O3 film and the ITO electrode were grown on the sapphire substrate by the radio frequency magnetron sputtering method at a low temperature. It is demonstrated that the Ga2O3 film is the single crystal film with the (−201) crystal plane orientation, and its bandgap can be obtained around 4.8 eV. Compared with the control tradsitional opaque PD with the Ti/Au metal electrode, the fully visible–transparent solar blind UV PD with the ITO electrode showed a larger photocurrent of 1.8 µA and responsivity of 181.03 A W−1 at the bias voltage of 20 V. The external quantum efficiency (EQE) even reached 88 198%, and photo-to-dark current ratio achieved 4.8 × 105. Besides, the PD with the ITO electrode also had a shorter response time and good electrical stability after multiple light cycles. The fabricated fully visible–transparent Ga2O3 solar blind UV PD is among the best reported Ga2O3 UV PDs and shows the great potential for the next generation of ‘see-through’ functional devices.

High performance solar-blind UV detector based on β-Ga2O3/GaN nanowires heterojunction

Gallium nitride nanowires and β-Ga2O3 nanowires were prepared by chemical vapor deposition. A solar-blind ultraviolet detector was fabricated based on β-Ga2O3/GaN nanowires heterojunction. The UV detector exhibits excellent response properties to deep ultraviolet with wavelength of 254 nm. The device exhibits a photo-to-dark current ratio of 1.375 × 103 and a high detectivity of 1.2 × 1011 Jones at 10 V bias Therefore, the responsivity of the UV detector is 27.5 mA/W under 254 nm ultraviolet light (8 mW/cm2) at 10 V bias voltage. The detector also has the advantages of easy preparation, low dark current, high rejection ratio, fast response, good stability and repeatability. The design method of β-Ga2O3/GaN nanowires heterojunction has the advantages of novelty and simplicity, which provides a new approach to fabricate a heterojunction detector.

Research on the Theoretical Model Between Solar-blind UV and Atmospheric Temperature during Atmospheric Transmission

In recent years,solar blind ultraviolet detection has been widely used in power fault detection.Based on atmospheric temperature profile and MODTRAN,we conduct simulation analysis on the influence of atmospheric temperature on solar blind ultraviolet atmospheric transmission.And finally the relationship between atmospheric temperature and ultraviolet atmospheric transmission was obtained through wavelength analysis and curve fitting.Based on the simulation relational expression,the quantitative analysis of atmospheric temperature and atmospheric transmission can be carried out,which can promote the study of the characteristics of solar blind ultraviolet transmission in the atmosphere and improve the accuracy of corona detection.

A flexible and transparent β-Ga2O3 solar-blind ultraviolet photodetector on mica

In the present work, we report a flexible transparent β-Ga2O3 solar-blind ultraviolet (UV) photodetector (PD) fabricated on a mica substrate. A laminated a-Ga2O3/Ga/a-Ga2O3 structure is thermally annealed at 1050 °C, forming a β-Ga2O3 film incorporating Ga nanospheres. A PD based on this nanocomposite film has a spectrum response peak at 250 nm, an extremely low dark current of 0.6 pA at a 10 V bias, a very high Ilight/Idark ratio of 3 × 106, and a fast recovery speed of less than 50 ms. Robust flexibility is demonstrated by bending tests and 10 000 cycles of a fatigue test with a radius as small as 8 mm. Compared to a room-temperature-fabricated flexible amorphous Ga2O3 (a-Ga2O3) PD, the flexible β-Ga2O3 PD on mica exhibits improved solar-blind UV photoresponse characteristics. The insertion of a gallium interlayer and treatment by high-temperature post annealing are proposed to contribute to a better stoichiometry and lattice order of the β-Ga2O3 thin film, as evidenced by the pronounced Raman peaks related to the GaI(OI)2 and GaIO4 vibration modes in β-phase Ga2O3. Our research is believed to provide a simple and practical route to achieving flexible transparent β-Ga2O3 solar-blind UV PDs, as well as other devices such as flexible transparent phototransistors and power rectifiers.

Self-powered solar-blind ZnGa2O4 UV photodetector with ultra-fast response speed

A novel self-powered solar-blind ZnGa2O4 ultraviolet (UV) photodetector has been constructed by fabricating asymmetric pairs of Au Schottky electrodes on the ZnGa2O4 film. The current-voltage curve of the device exhibits an obvious rectifying characteristic with a rectification ratio of 11.3 at ±8 V. At 0 V bias, the peak responsivity of our device at 246 nm is about 22.2 mA/W with an UV–vis rejection ratio of 1.3×104, indicating the excellent self-powered solar-blind UV photodetector performance. More interestingly, the rise time and decay time of the device are only 10 ns and 30 ns, respectively, which are much faster than that of any other previously reported self-powered solar-blind UV photodetectors to the best of our knowledge. The ultra-fast response speed of the device should be attributed to the asymmetric Schottky junctions and the high crystalline quality of our ZnGa2O4 film with low trap density. Our work provides a new method to constructing high-performance self-powered solar-blind UV photodetectors.

3D-to-2D Dimensional Reduction for Exploiting a Multilayered Perovskite Ferroelectric toward Polarized-Light Detection in the Solar-Blind Ultraviolet Region.

Polarized-light detection in solar-blind ultraviolet region is indispensable for optoelectronic applications, whereas new 2D candidates targeted at solar-blind UV range remain extremely scarce. 2D hybrid perovskite ferroelectrics that combine polarization and semiconducting properties are of increasing interest. Here, using the 3D-to-2D dimensional reduction of CH3 NH3 PbCl3 , we designed a multilayered hybrid perovskite ferroelectric, (CH3 CH2 NH3 )2 (CH3 NH3 )2 Pb3 Cl10 , which shows spontaneous polarization and a high Curie temperature (390 K) comparable with that of BaTiO3 (393 K). The wide band gap (ca. 3.35 eV) and anisotropic absorbance stemming from its intrinsic 2D motif, greatly favor its polarization-sensitive activity in UV region. The device displays excellent polarization-sensitive behavior under 266 nm, along with a large dichroic ratio (ca. 1.38) and high on/off current ratio (ca. 2.3×103 ).

Y2O3: Eu3+/PMMA hybrid film as a converter for enhanced harvesting of broadband solar-blind UV light.

At present, the most common materials for solar-blind UV light detectors are wide band-gap semiconductors, which generally have high requirements and complex methods for preparation. Ordinary semiconductor materials such as silicon, TiO2, and Cu2O were industrialized, but they were excluded for direct harvest of solar-blind UV light due to their inability to absorb solar-blind light photons. Here, inorganic-organic hybrid film of Y2O3:Eu3+/PMMA was used as a spectral converter to realize the detection of broadband solar-blind UV light by ordinary semiconductor, converting broadband solar-blind UV luminescence to visible luminescence based on down-conversion process, after which the visible luminescence was detected by the Si photo-resister. The results show that hybrid film based on rare earth luminescence materials is particularly valuable for broadband solar-blind UV detection.

Effects of annealing process on the structural and photodetection properties of new thin-film solar-blind UV sensor based on Si-photonics technology

In this paper, a new heterojunction structure based on ultrathin-film ITO sputtered on non-hydrogenated amorphous-silicon (a-Si) is developed for high-detectivity solar-blind UV-photodetector (UV-PD) based on silicon (Si) photonics technology. A strategic combination of Particle Swarm Optimization (PSO) and numerical analysis is used to find out the best design offering superior optoelectronic performance. The optimized design is then elaborated using RF magnetron sputtering technique. A comprehensive investigation of the device structural and optoelectronic properties was carried out, incorporating the influence of heat treatment at temperature values ranging from 300°C to 600°C. X-Ray Diffraction (XRD) measurements indicate that the crystallinity of the sputtered layers was enhanced by increasing the annealing temperature. Significantly, photoelectrical characterization showed that the annealed ITO/a-Si UV-PD exhibits high detectivity exceeding 1013 Jones with a highly improved UV-to-Vis rejection ratio of 5.7 × 103. The ITO/a-Si heterojunction generated a built-in potential, enabling effective separation and transport of photo-induced carriers, thereby reducing recombination losses. Therefore, by well optimizing the proposed heterostructure and the annealing conditions, we were able to elaborate new highly detective, thin-film solar-blind UV-PD based on Si-photonics platform, which can be a promising alternative for future high-performance and cost-effective optoelectronic systems.

Effective light absorption by graded Al-component AlxGa1-xN nano-array photocathode with light trapping effect

Nanowire arrays (NWAs) have sufficient “light trapping effect” to more efficiently collect sunlight. Due to the excellent detection background of the solar blind band UV detector, and in order to improve the quantum efficiency of the photocathode, the core component of the detector, the graded Al-component AlxGa1-xN nanowire arrays (NWAs) photocathode with the built-in electric field is proposed. Based on the geometric optimization of wave optics, the effects of the number of layers and the thickness of the graded compositional nanowires on light absorption are also studied, and we designed three kinds of graded Al-component AlxGa1-xN nano-arrays with variable structure (nano-cylinder, truncated nano-cones, nano-cones). The results show that the conical nanowires can enhance the light-trapping ability of the solar-blind band and obtain the high sensitivity characteristics of the threshold wavelength, which effectively concentrate the light in the center of nanostructure. Therefore, we strongly recommend the introduction of conical nanostructures to address the high reflectance and carrier lifetime of short-wavelength UV detectors, which would be a beneficial innovation for graded Al-component AlxGa1-xN NWAs photocathodes.

High performance solar-blind UV detector based on Hf0.38Sn0.62O2 epitaxial film

In this work, high-quality SnO2 and Hf0.38Sn0.62O2 thin films were grown on c-plane sapphire substrates by pulsed laser deposition for a comparative study. The optical and electrical tests show that Hf doping leads to significantly increased bandgap and resistivity of the HfSnO2 alloy as compared to SnO2. Then, SnO2- and Hf0.38Sn0.62O2-based UV detectors were fabricated and compared. The Hf0.38Sn0.62O2 film-based detector exhibits an excellent performance. Its dark current is as low as 0.2 pA under 20 V, and the rise/decay response time is as short as 69 ms/50 ms. The cut-off wavelength and the rejection ratio are 290 nm and 4100, respectively. Our work demonstrates that the Hf0.38Sn0.62O2 ternary alloy compound semiconductor has great potential for applications in solar-blind ultraviolet detections.

Anti-Fog Imaging and Ship Positioning and Berthing Method Based on Solar-Blind Ultraviolet Optical Electronic Signal

The foggy environment, particularly in the dense fog, would significantly weaken the general optical imaging capability. In such condition, common optical imaging methods could hardly recognize targets and self-position in an effective manner, severely impacting ship berthing operation. Targeted at ship berthing in foggy days and based on zero background interference of solar-blind ultraviolet (UV) optical electronic signal, calibration and imaging positioning method based on solar-blind UV imagers were studied here, achieving three-dimension positioning with high precision. Direct imaging and accurate positioning for assisting in ship berthing could be realized at the same time. In this article, local positioning effect in the foggy environment was evaluated by applying solar-blind UV imaging band. The measurement results verify that accurate positioning could be achieved in the foggy environment by solar-blind UV anti-fog imaging positioning approach to satisfy demands of ship berthing in foggy days.

UV Photodetection: Atomically Thin Oxyhalide Solar‐Blind Photodetectors (Small 23/2020)

In article number 2000228, Luying Li, Tianyou Zhai, and co-workers prepare large-size BiOCl flakes with thickness down to a monolayer via salt-assisted chemical vapor deposition. The 2D BiOCl photodetectors exhibit high responsivity throughout the solar-blind range at room and high temperatures. The success in fabrication of atomically thin BiOCl photodetectors opens opportunities for their potential applications in solar-blind UV photodetection.