Solar Blind Research Articles

Effects of the Interface Properties on the Performance of UV-C Photoresistors: Gallium Oxide as Case Study.

Electrical contacts are of the greatest importance as they decisively contribute to the overall performance of photoresistors. Undoped κ-Ga2O3 is an ideal material for photoresistors with high performance in the UV-C spectral region thanks to its intrinsic solar blindness and extremely low dark current. The quality assessment of the contact/κ-Ga2O3 interface is therefore of paramount importance. The transfer length method is not applicable to undoped Ga2O3 because the interface with several metals shows a non-ohmic character, and a non-equivalent contact resistance could restrict its applicability. In this work, a new methodological procedure to evaluate the quality of contact interface and its effect on the sensing performance of UV-C photoresistors is presented, using the SnO2-x/κ-Ga2O3 contact interface as a case study. The proposed method includes a critical comparison between two-point and four-point probe measurements, over a wide range of voltages. The investigation showed that the effect of contact resistance is more pronounced at low voltages. The presented method can be easily extended to any kind of metal/semiconductor or degenerate-semiconductor/semiconductor interface.

Geometrical optimization of solar venetian blinds in residential buildings to improve the economic costs of the building and the visual comfort of the residents using the NSGA-II algorithm

The entering sunlight from the building's windows mainly affects the heating and visual comfort of the occupants. The applications of Venetian blinds are a solution to improve the heating and visual comfort of the occupants. However, reducing the sunlight that enters the space can result in a rise in the building's electricity consumption. While most studies focus on the electricity production of solar panels, present study aims to examine the effect of solar venetian blinds on the indoor visual and thermal comfort of the occupants and optimize their geometry considering different geographical specifications. In the present paper, efforts are made to numerically install solar panels on Venetian blinds and analyze the effect of changing the geometrical parameters of solar Venetian blinds and the building's window dimensions on visual comfort and net electricity. Therefore, the target functions in the present paper are an improvement percentage in the daylight glare index and an improvement percentage in the net electricity costs for the analyzed building. As a result, five cities in Iran that have different climatic conditions are targeted to model the building. EnergyPlus software is employed to conduct the energy-based calculations, and the design variables and target functions are defined using JEPLUS software. The outputs are next inserted in JEPLUS+EA software to process a multi-objective optimization using the NSGA-II algorithm. The results demonstrate that the visual comfort and net electricity can be optimized by ranges of 10–100% and 1.5–10%, respectively. Furthermore, Venetian blinds are proven to have higher reception of sun radiations and better efficiency in southern cities and they can have a more proper performance while being installed for windows of southern building wall.

Highly Sensitive Narrowband AlGaN Solar Blind Ultraviolet Photodetectors Using Polarization Induced Heterojunction Barrier

Highly Sensitive Narrowband AlGaN Solar Blind Ultraviolet Photodetectors Using Polarization Induced Heterojunction Barrier

Enhanced Responsivity of Solar Blind Ultraviolet Photodetector by PEALD Deposited Zn-Doped Ga2O3 Thin Films

Enhanced Responsivity of Solar Blind Ultraviolet Photodetector by PEALD Deposited Zn-Doped Ga₂O₃ Thin Films

Vertical asymmetric metal-semiconductor-metal photodiode based on β-Ga2O3 thin films fabricated via solution process for arc discharge detection

Arc discharge detection is a preeminent strategy for diagnosing aging of high-power electric equipment. Therefore, the timely detection of arc discharge can prevent immense disasters, such as massive fire accidents. Ultraviolet C (UVC) photodetectors (PD) are effective devices for optical arc discharge detection because of their solar blindness, which enables noise-free and highly selective arc discharge detection. In this study, we developed a solution-processed β-Ga2O3-based vertical asymmetric metal-semiconductor-metal (MSM) UVC PD as a high-performance and inexpensive UVC detector. The high bandgap of photoactive β-Ga2O3 (4.7–5.1 eV) enables selective UVC detection. The Schottky barrier heights at two different metal-semiconductor junctions (PEDOT:PSS/β-Ga2O3 and ITO/β-Ga2O3) were systematically modulated by varying the β-Ga2O3 film annealing temperature and thickness, which enabled fast photoresponse and self-powered operation, as demonstrated by various optical and electrical analyses. The optimized device exhibited a fast photoresponse (rise/fall time of 67/53 ms) and high responsivity (41 mA W−1) and detectivity (1.5×1011 Jones) in self-powered mode. The instantaneous arc discharge was successfully detected using the β-Ga2O3 based vertical MSM PD, demonstrating its feasibility for arc discharge detection. Thus, this study provides new insights into inexpensive self-powered PDs that can be implemented for the facile and prompt monitoring of aging electric equipment and prevention of potential fire accidents.

Photovoltaics literature survey (No. 181)

Photovoltaics literature survey (No. 181)

Evaluation of Building Energy Savings Achievable with an Attached Bioclimatic Greenhouse: Parametric Analysis and Solar Gain Control Techniques

Bioclimatic solar greenhouses are passive solar systems of relevant interest in the building sector, as they allow the reduction of energy needs related to air-conditioning. The aim of this work is to analyze the thermal behavior of a bioclimatic solar greenhouse attached to a residential building. It is equipped with photovoltaic solar blinds (SPBs) to manage solar inputs and produce electricity. Automated control systems are implemented to activate the vents and SPBs. The parametric performance analysis conducted using the dynamic simulation software EnergyPlus allowed the evaluation of the influence of glass type, thermal mass, size, ventilation and location. The results show how the automation of the vents allows the maximization of heat exchange throughout the year, leading to a reduction in consumption even during the summer period. Analyses conducted for some cities in the Mediterranean area show that the maximum energy saving obtained is greater than 13%; in addition, photovoltaic solar shading contributes to the production of more than 1000 kWh/year of electricity.

Building-integrated photovoltaics (BIPV): A mathematical approach to evaluate the electrical production of solar PV blinds

Lower prices for photovoltaic systems lead to the spread of building-integrated photovoltaics (BIPV). In this paper, a simple method is proposed to evaluate the electrical power produced by Solar Photovoltaic Blinds (SPB). The equations allow to assess slat mutual shading and view factors and are applicable to any slat inclination, any orientation and any geometry. The possibility that the PV layer does not entirely cover the lamella is also considered. A parametric study is performed to evaluate the impact of geometric factors on the annual yield. The paper shows that 1) The south-east (or -west) orientation provides maximum electrical production. 2) Automating closing PV blinds in summer, when room is unoccupied, allows to increase electricity production by approximately 9% for the south, east and west exposures and 16% for the north exposure. 3) There is a slat distance/width ratio that maximizes the annual electricity produced. It depends on the handling strategy and is about 0.6 for energy optimizing methods and 0.7 for standard uses. 4) Solar tracking that maximizes the radiation entering the room in winter significantly reduces electricity production. 5) The reflectivity of the back of the slats has a little influence on the annual production (up to 5%).

Effects of geometric parameters on photoemission of AlGaN nanowire array photocathode

In recent years, with the continuous development of solar blind ultraviolet photodetectors, III-V compounds are widely used as semiconductor materials. The nanowire array structure has excellent ‘light trapping effect’. However, if the distance of nanowire is too close, the secondary absorption problem of the nanowire will occur. If the distance of nanowire is too far, the number of photocarriers generated in the nanowire array per unit volume will be reduced. Meanwhile, the absorption capacity of the nanowire structure with different shapes is different. Based on this background, we studied the influence of the period and geometry of AlGaN nanowires with different Al components on the optical response properties. The finite time domain difference (FDTD) method was used to compare the quantum efficiency and collection efficiency of AlGaN nanowires with different Al components, we found that the quantum efficiency of the hexagonal nanowire array with Al component of 0.42 is as high as 45%, which is the highest in our structure. At the same time, its cutoff wavelength is at 280 nm, which has excellent solar blindness. Therefore, the study in this paper can provide some theoretical reference for the experiment and preparation of AlGaN photocathode.

Solar‐Blind Ultrathin Sn‐Doped Polycrystalline Ga2O3 UV Phototransistor for Normally Off Operation

Deep ultraviolet (DUV) photodetectors (PDs) based on ultrawide bandgap β‐Ga2O3 have great potential for aerospace, military, and civilian applications, especially because of their inherent solar blindness. An 8 nm thick Sn‐doped polycrystalline β‐Ga2O3 semiconductor is used as the channel material for a solar‐blind PD in this study. The β‐Ga2O3 channel is fully depleted by upward bending of the energy band owing to the work function difference between the highly p‐type Si (gate electrode) and β‐Ga2O3, resulting in normally off behavior with a positive threshold voltage under dark conditions. The normally off behavior is beneficial for simplicity of the gate‐driver circuitry and low power consumption under standby conditions. The fully depleted 8 nm thick polycrystalline β‐Ga2O3 exhibits high‐performance DUV detection capability of light at 215 nm: a low dark current of 29.3 pA and high photo‐to‐dark‐current ratio of ≈104 at zero gate voltage. This fully depleted n‐type β‐Ga2O3 semiconductor with a wafer‐scale substrate can expedite the realization of high‐performance and low‐power‐consumption solar‐blind PDs.

Exfoliated and bulk β-gallium oxide electronic and photonic devices

<h2>Abstract</h2> Monoclinic gallium oxide (β-Ga₂O₃) has recently attracted increasing attention due to the availability of high quality, large diameter single crystals from mature melt growth methods and its attractive material properties of wide E_G of 4.6–4.9 eV, good electron mobility (>200 cm²/Vs) and estimated E_c of ~8 MV/cm. Compared to other ultra-wide bandgap materials, the inexpensive substrates lower the manufacturing cost for β-Ga₂O₃ power devices. Applications of deep-UV detectors with solar blindness include inspection of high voltage transmission lines for corona and partial discharges, detection of fires and various defense systems. Si- and GaAs-based UV PDs are not truly solar-blind, as additional, bulky visible-light blocking filters are required. In this short review we discuss the use of bulk and exfoliated β-Ga₂O₃ for these applications and relate this to the basic surface and response of the material to high temperatures, radiation exposure and typical semiconductor processing steps. The material can easily be cleaved along the (100) surface and layers with (100)A surface termination have higher energy than the (100)B termination. The (100)B cleavage plane is the favorable one, observed experimentally.

Self-powered solar-blind ultrafast UV-C diamond detectors with asymmetric Schottky contacts

Single-crystal chemical vapour deposition (CVD) diamond samples with asymmetric Schottky contacts were used for the fabrication of vertical metal-semiconductor-metal detectors for deep ultraviolet (UV–C) radiation. Spectral photoconductivity measurements, performed in the 190 ÷ 1100 nm wavelength range, returned an ultraviolet-to-visible (UV/Vis) rejection ratio of 6.8 × 103 under photovoltaic operating conditions, ensuring solar blindness and zero power consumption at the same time. When applying bias, UV/Vis rejection ratio reached excellent values (>104) even at very low electric fields (0.01 V/μm), thanks to the excellent structural quality and the superior charge transport properties of the diamond bulk, as inferred from Raman analysis and spectral photoconductivity measurements. Mobility-lifetime (μτ) product of the photogenerated carriers was indeed measured to be about 5 × 10−3 cm2/V in the case of holes, which is the highest room-temperature μτ value ever reported for CVD diamond, enabling a response speed in the nanosecond range even at zero-bias operating conditions.

Effect of Modified Silica Materials on Polyvinyl Chloride (PVC) Substrates to Obtain Transparent and Hydrophobic Hybrid Coatings

In this research, we report a simple and inexpensive way to prepare transparent and hydrophobic hybrid coatings through deposition of different silica materials on polyvinyl chloride (PVC) substrates. The silica materials were prepared using an acid-catalyzed sol–gel method at room temperature (25 ± 2 °C), using alkoxysilanes: tetraethoxysilane (TEOS), as the silica source, and ethoxydimethylvinylsilane (DMVES), triethoxyoctylsilane (OTES), and trimethoxyhexadecylsilane (HDTMES), as modifier agents. The obtained materials were characterized (either as powders or as thin films) by Fourier-transform infrared spectroscopy (FTIR), UV/Vis spectroscopy, transmission electron microscopy (TEM), thermogravimetric analysis (TGA), atomic force microscopy (AFM), spectroscopic ellipsometry (SE), and water contact-angle measurements. UV/Vis spectra showed that the PVC substrate coated with the silica material containing TEOS/DMVES/OTES had a transmittance of about 90% in the wavelength range of 650–780 nm. The water contact angles increased from 83° for uncoated PVC substrate to ~94° for PVC substrates coated with the sol–gel silica materials. These PVC films with hybrid silica coatings can be used as the materials for outdoor applications, such as energy-generating solar panel window blinds or PVC clear Windmaster outdoor blinds.

Self-powered solar-blind α-Ga2O3 thin-film UV-C photodiode grown by halide vapor-phase epitaxy

A compact self-powered solar-blind UV-C photodiode was demonstrated using an ultra-wide bandgap (UWBG) α-Ga2O3 thin film as a wavelength-selective absorber layer. The UWBG-based Schottky junction architecture renders the use of low-performance and bulky solar-blind UV bandpass filters unnecessary. High-quality α-Ga2O3 thin films with a thickness of 1.25 µm were grown on a (0001) sapphire substrate via the halide vapor-phase epitaxy technique. The self-powered solar-blind UV-C photodetector based on the Ni/α-Ga2O3 Schottky junction exhibited excellent responsivity (1.17 × 10−4 A/W), photo-to-dark current ratio (1.12 × 105), and reproducibility, as well as fast rise/decay characteristics without persistent photoconductivity upon exposure to UV-C radiation (254 nm wavelength). The relationship between light intensity (I) and photocurrent (P) was modeled by I ∼ P0.69, indicating the high-quality of the halide vapor-phase epitaxy-grown α-Ga2O3 thin film. Upon exposure to natural sunlight, the fabricated solar-blind photodetector showed excellent solar blindness with sensitivity to UV-C radiation and did not require an external power source. Therefore, this UWBG α-Ga2O3 thin-film Schottky barrier photodiode is expected to facilitate the development of a compact and energy-independent next-generation UV-C photodetector with solar blindness.

Heteroepitaxial growth of high Mg-content single-phased W-MgZnO on ZnO matrixes in various nucleation states for solar-blind and visible-blind dual-band UV photodetectors

High Mg-content single-phase wurtzite Mg0.51Zn0.49O (W-Mg0.51Zn0.49O) films were realized by radio frequency (RF) magnetron sputtering technique on quartz (SiO2) substrates. The metal-semiconductor-metal (MSM) solar-blind (SB) and visible-blind (VB) dual-band ultraviolet (DB-UV) photodetectors (PDs) were also fabricated based on heteroepitaxial growth of W-Mg0.51Zn0.49O films on ZnO buffer layer (BL) at different nucleation states. Under 270 nm of irradiation, the Au/Mg0.51Zn0.49O/ZnO (30 min) PD exhibited an optimal external quantum efficiency (EQE, 304.4%) and specific detectivity (1012), which indicated that the ZnO BL obtained with a 30 min treatment time was most efficient to improve the detection of SB-UV wavelength. The origin of these results was attributed to the contact area and adhesion strength between MgZnO and ZnO matrices. The results showed a feasible way to obtain high Mg-content wurtzite MgZnO alloys and performance improvement through ZnO BL, which is favorable to the applicability in SB/VB DB-UV PDs.

Highly selective ozone-treated β -Ga2O3 solar-blind deep-UV photodetectors

The ultra-wide energy bandgap (4.6–4.9 eV) of the β-Ga2O3 semiconductor offers intrinsic solar blindness, which is a great advantage as the absorber material of a deep ultraviolet (UV) photodetector. Although the band-to-band excitation transition in β-Ga2O3 is allowed solely by the UV-C wavelength, the defective sites including oxygen vacancies can induce sub-bandgap absorption, resulting in high background noise. The UV-ozone treatment was performed at elevated temperatures to investigate its effect on removing these oxygen vacancies; it creates reactive oxygen radicals that can reach the β-Ga2O3 lattice and passivate the defective sites. The chemical analysis through x-ray photoelectron and micro-Raman spectroscopies revealed an increase in Ga–O bonding after UV-ozone treatment. The optoelectrical measurements on the β-Ga2O3 UV-C photodetectors showed that the UV-ozone treatment significantly decreased the response to UV-A light. Thus, the photodetector performance (photo-to-dark current ratio, responsivity, detectivity, and rejection ratio) was greatly enhanced; especially, the rejection ratio was increased to 4.56 × 108 by eight orders of magnitude after UV-ozone treatment. The remarkably improved UV-C selectivity in the β-Ga2O3 solar-blind photodetector highlights its potential of realizing truly solar-blind photodetectors using a simple UV-ozone treatment technique.

Lyman Continuum Escape Fraction from Low-mass Starbursts at z = 1.3*

Abstract We present a new constraint on the Lyman continuum (LyC) escape fraction at . We obtain deep, high sensitivity far-UV imaging with the Advanced Camera for Surveys Solar Blind Channel on the Hubble Space Telescope, targeting 11 star-forming galaxies at 1.2 &lt; z &lt; 1.4. The galaxies are selected from the 3D-HST survey to have high Hα equivalent width (EW) with an EW &gt; 190 Å, low stellar mass (M * &lt; 1010 M ⊙), and U-band magnitude of U &lt; 24.2. These criteria identify young, low metallicity star-bursting populations similar to the early star-forming galaxies believed to have reionized the universe. We do not detect any LyC signal (with a signal-to-noise ratio &gt; 3) in the individual galaxies or in the stack in the far-UV images. We place 3σ limits on the relative escape fraction of individual galaxies to be and a stacked 3σ limit of . Measuring various galaxy properties, including stellar mass, dust attenuation, and star formation rate, we show that our measured values fall within the broad range of values covered by the confirmed LyC emitters from the literature. In particular, we compare the distribution of Hα and [O III] EWs of confirmed LyC emitters and non-detections, including the galaxies in this study. Finally, we discuss if a dichotomy seen in the distribution of Hα EWs can perhaps distinguish the LyC emitters from the non-detections.

High gain, large area, and solar blind avalanche photodiodes based on Al-rich AlGaN grown on AlN substrates

We demonstrate large area (25 000 μm2) Al-rich AlGaN-based avalanche photodiodes (APDs) grown on single crystal AlN substrates operating with differential (the difference in photocurrent and dark current) signal gain of 100 000 at 90 pW (&amp;lt;1 μW cm−2) illumination with very low dark currents &amp;lt;0.1 pA at room temperature under ambient light. The high gain in large area AlGaN APDs is attributed to a high breakdown voltage at 340 V, corresponding to very high breakdown fields ∼9 MV cm−1 as a consequence of low threading and screw dislocation densities &amp;lt; 103 cm−2. The maximum charge collection efficiency of 30% was determined at 255 nm, corresponding to the bandgap of Al0.65Ga0.35N, with a response of 0.06 A/W. No response was detected for λ &amp;gt; 280 nm, establishing solar blindness of the device.

快焦比长焦距日盲紫外光学系统设计

快焦比长焦距日盲紫外光学系统设计

Toward AlGaN Focal Plane Arrays for Solar‐Blind Ultraviolet Detection

Missile approach warning (MAW) systems of airborne military platforms require ultrasensitive detection capabilities in the solar‐blind UV regime below 280 nm. Today, these needs are answered with UV photomultiplier tubes, which are bulky, complex, and require external filtering to suppress clutter signatures beyond 280 nm.This study investigates whether AlGaN focal plane array (FPA) detectors may develop into a viable alternative. The compact, lightweight, all‐solid‐state solution promises intrinsic solar blindness and excellent out‐of‐band suppression ratios realizable at affordable costs on large‐area substrates. Yet, does today's state of technology allow mastering the fabrication processes so that the electrooptical performance is sufficient to achieve the required sensitivity? Herein, three device wafers are grown by metalorganic chemical vapor deposition and subsequently processed into detector arrays with a spatial resolution of 640 × 512 pixels on a 15 μm pitch. After hybridization with an off‐the‐shelf capacitive transimpedance input amplifier (CTIA) read‐out integrated circuit (ROIC), their electrooptical performance is characterized. The characterized FPAs show a very low percentage of defective pixels, excellent linearity at high photon fluxes, and, at low flux, their already remarkable sensitivity is limited by the off‐the‐shelf CTIA ROIC. Therefore, with further improvements MAW systems based on AlGaN FPAs seem feasible.