Solar-blind Ultraviolet Detection Research Articles

Ternary compound MgTiO3 combined with graphene for solar-blind deep ultraviolet photodetection

Ternary materials have gained great popularity in the field of solar-blind ultraviolet (UV) photodetectors due to their diverse band gaps. Whereas, quality problems brought by lattice damage and phase separation appear frequently during preparation, which greatly limit the application of ternary solar-blind photoresponsive materials. MgTiO3 (MTO), a ceramic material, has extensive application in microwave capacitors and dielectric resonators but takes no place in the field of photodetectors. Faced with this situation, this study investigates the effect of annealing on the structure of MTO thin film, and fabricates a solar-blind UV detector through combining MTO with graphene, which expands the application of ternary compound MTO to the field of photodetectors. Under solar-blind UV illumination, this MTO-based detector exhibits excellent performance with an open circuit voltage as high as 1.7 V. At 0 V bias, the detector exhibits an ultrafast response speed with the rise and decay time as short as 30 ms and 25 ms, respectively. Besides, a responsivity up to 46.5 mA/W, an external quantum efficiency (EQE) up to 20.4%, and a specific detectivity (D*) up to 6.14 × 1011 Jones also prove the great performance this detector owns. All the results achieved in this work not only suggest the great potential of MTO in being applied to fabricating solar-blind UV detectors, but also provide some guidance for the development of photovoltaic detectors based on other ternary semiconductor materials.

Ultra-low dark current back-illuminated AlGaN-based solar-blind ultraviolet photodetectors with broad spectral response

A high performance AlGaN-based back-illuminated solar-blind ultraviolet (UV) p-i-n photodetectors (PDs) are fabricated on sapphire substrates. The fabricated PD exhibits ultra-low dark current of less than 0.15 pA under -5 V bias, which corresponds to a dark current density of <1.5×10-11 A/cm2. In particular, the PD shows broad spectral response from 240 nm to 285 nm with an excellent solar-blind/UV rejection ratio of more than 103. The peak responsivity at the wavelength of 275 nm reaches 0.19 A/W at -5 V, corresponding to a maximum quantum efficiency of approximately 88%. Based on the absence of any anti-reflection coating, this corresponds to nearly 100% internal quantum efficiency. In addition, the PD shows a quite fast response of 0.62 ms. To the best of our knowledge, this is the record low dark current density and broadest response band reported for the back-illuminated AlGaN-based solar-blind UV detectors.

Na+-doped lead-free double perovskite Cs2AgInCl6 for broadband solar-blind UV detection

As a new generation of photonic materials, lead-free halide double perovskite materials demonstrate strong UV-light excited broadband emission that are promising for solar-blind ultraviolet (UV) light detectors. However, their practical applications are strongly limited by the low photoluminescence quantum efficiency because of the parity-forbidden nature of electronic transitions. Herein, the idea of cation alloying into lead-free halide double perovskite is proposed to mitigate the weak electronic transition and to improve the luminescence yield. By using the hydrothermal method, a series of Cs2NaxAg1-xInCl6 microcrystals were fabricated and the influences of Na-doping on the structural evolution and optical properties are investigated. Notably, the luminescence properties can be greatly improved by introducing an alloying element. By leveraging the UV-to-visible spectral conversion capability of the developed halide crystals, we fabricated a luminescent composite film by incorporating Cs2NaxAg1-xInCl6 perovskite nanocrystals into a polymethyl methacrylate matrix. Using this composite film as a spectral converter, we successfully demonstrated a solar-blind ultraviolet light detector with broadband and efficient response. Our work provides a novel solution for broadband solar-blind UV detection that could have practical implications for commercialization of metal halide based luminescent materials.

Solar-blind ultraviolet detector based on ordered nanoporous β-Ga2O3 film

The β-Ga2O3 ultraviolet (UV) detectors work in the solar-blind (UV) band due to the ultra-wide bandgap of β-Ga2O3. In this paper, a solar-blind ultraviolet detector based on an ordered nanoporous β-Ga2O3 (ONP-β-Ga2O3) film is proposed and implemented. The local enhancement effect of the ordered nanopores on light is simulated by finite-difference time-domain method, and the period and diameter of the nanopores are optimized. Graphene is transferred on the ONP-β-Ga2O3 film and prepared as interdigital electrodes of the solar-blind ultraviolet detectors. The optimal detector has a photo-to-dark current ratio of about 4.64 × 103 at a 5 V bias, a peak response of 2.43 A W−1 at 254 nm, and a UV/visible rejection ratio of about 1081. We demonstrate that the ordered nanoporous structure can localize optical field effectively, which results in enhancement of light absorption as well as improvement of key detector parameters.

Solar-blind ultraviolet detector based on ordered nanoporous β-Ga2O3 film

Abstract The β-Ga2O3 ultraviolet (UV) detectors work in the solar-blind (UV) band due to the ultra-wide bandgap of β-Ga2O3. In this paper, a solar-blind ultraviolet detector based on an ordered nanoporous β-Ga2O3 (ONP-β-Ga2O3) film is proposed and implemented. The local enhancement effect of the ordered nanopores on light is simulated by finite-difference time-domain (FDTD) method, and the period and diameter of the nanopores are optimized. Graphene is transferred on the ONP-β-Ga2O3 film and prepared as interdigital electrodes of the solar-blind ultraviolet detectors. The optimal detector has a photo-to-dark current ratio (PDCR) of about 4.64×103 at a 5 V bias, a peak response of 2.43 A/W at 254 nm, and a UV/visible rejection ratio of about 1081. We demonstrate that the ordered nanoporous structure can localize optical field effectively. As a result, light absorption is enhanced, and response performances of the detector are improved evidently.

Solar-blind UV detection by ultra-wide-bandgap 4HCB organic single crystal semiconductor

In this work, the solar-blind ultraviolet (UV) detection performance of organic single crystals 4-hydroxycyanobenzene (4HCB) is demonstrated. The ultra-wide bandgap and low dark current make 4HCB an important candidate for this application. Detectors with two electrode configurations, i.e., sandwiched electrode (SWE) and interdigital electrode (IDE), are fabricated based on 4HCB single crystals and measured under the illumination of 254 nm-UV light. Apparently, the IDE detector exhibits a responsivity R of 14 000 μA W−1 at a bias voltage of 1000 V, which is 2000 times higher than that of the SWE detector, due to its enhanced photoconductive gain by the surface layer edge states. To explore the possibility for the space UV detection applications in the radiation environment, the effect of neutron radiation on 4HCB detector performance is revealed. The point defects introduced by fast neutrons, mainly H vacancies, dominate the variation of the Fermi energy level and electric properties; however, this effect on photodetection is limited when the neutron flux is below 1013 n cm−2.

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In this work, β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; films with different thickness are prepared on (001) sapphire substrates at room temperature by the radio frequency magnetron sputtering technology, then the samples are annealed in an Ar atmosphere at 800 ℃ for 1h. The effects of film thickness on the phase composition, surface morphology, optical property, and photoelectric detection performance are investigated using XRD, SEM, UV-Vis spectrophotometer, PL photoluminescence spectrometer, and Keithley 4200-SCS semiconductor characterization system. The results show that as the film thickness increases, the film crystallinity is improved, films with a thickness of 840 nm exhibit best quality, while those with a thickness of 1050 nm declines a little in quality. The β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; films with different thickness exhibit obvious ultraviolet light absorption in the solar-blind region with wavelengths of 200–300 nm, and the bandgap width increases with the film thickness increasing. All the β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; films show a broad UV-green light emission peaks in a wavelength range of 350–600 nm. As the film thickness increases, the intensities of the emission peaks of ultraviolet, violet, and blue light are greatly reduced, indicating that oxygen vacancy-related defects (&lt;i&gt;V&lt;/i&gt;&lt;sub&gt;O&lt;/sub&gt;, &lt;i&gt;V&lt;/i&gt;&lt;sub&gt;Ga&lt;/sub&gt;–&lt;i&gt;V&lt;/i&gt;&lt;sub&gt;O&lt;/sub&gt;) are greatly suppressed with film thickness increasing. Solar-blind ultraviolet photodetector is fabricated based on the β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; film. Its photoelectric detection performances (the photo-to-dark current ratio, responsivity, detectivity, and external quantum efficiency) also increase first and decrease then with the increase of film thickness. The β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; ultraviolet photodetector prepared by a thin film with a thickness of 840 nm exhibits a very low dark current (4.9 × 10&lt;sup&gt;–12&lt;/sup&gt; A) under a 5 V bias voltage and an ultraviolet light with a wavelength of 254 nm (600 μW/cm&lt;sup&gt;2&lt;/sup&gt;). It exhibits a high photo-to-dark current ratio of 3.2 × 10&lt;sup&gt;5&lt;/sup&gt;, and a short response time of 0.09/0.80 s (rising time) and 0.06/0.53 s ratio (falling time). Its responsivity (&lt;i&gt;R&lt;/i&gt;), detectivity (&lt;i&gt;&lt;u&gt;D&lt;/u&gt;&lt;/i&gt;&lt;sup&gt; *&lt;/sup&gt;), and the external quantum efficiency (EQE) are 1.19 mA/W, 1.9 × 10&lt;sup&gt;11&lt;/sup&gt; Jones, and 0.58%, respectively. The prepared device has quantifiable characteristics, and its photocurrent increases almost linearly with the increase of applied voltage and optical power density, and therefore can work in a linear dynamic region, which indicates that it is very suitable for fabricating the solar-blind ultra-violet detectors.

Ultrahigh EQE (38.1%) Deep‐UV Photodiode with Chemically‐Doped Graphene as Hole Transport Layer

AbstractImproving the open‐circuit voltage (VOC) is a fundamental target for photovoltaic devices to obtain high photoelectric conversion efficiency (PCE). Here, it is reported that the chemical doping of graphene hole transport layer has a significant impact on the VOC of solar‐blind ultraviolet (SBUV) photovoltaic detectors. It has been demonstrated that the external quantum efficiency (EQE) of graphene/AlGaN/SiC heterojunction photovoltaic detectors increases from 21.6% to 38.1% when the Fermi level of graphene is precisely pulled down by a simple charge transfer process. Without sacrificing response speed, the ≈75% increase in EQE together with responsivity is the result of the enhancement of VOC from 1.10 to 2.02 V. This work sheds light on the correlation between VOC and graphene Fermi level in SBUV detectors, and provides effective avenues to modulate the PCE of photovoltaics.

A Solar-Blind Ultraviolet Photodetector With Graphene/MgZnO/GaN Vertical Structure

Graphene (Gr) has high transmittance to ultraviolet (UV) light and high mobility, which can effectively collect and transfer carriers. In this work, MgZnO (MZO) films were grown on the surface of the p-GaN by magnetron sputtering. A heterojunction solar-blind UV detector with Gr/MZO/GaN structure was constructed by introducing Gr as the window layer film. The test results show that the device has excellent detection ability for solar-blind UV light. The light response cut-off edge of the device is 263 nm, under the illumination of 255 nm and the bias voltage of −5 V, the responsivity is 14.6 mA/W, the rise time is 0.79 s, the decay time is 0.2 s, and the external quantum efficiency is 71.1%. The importance of this work lies in providing a reference for the application of Gr-based photodetectors.

Fermi-Surface Modulation of Graphene Synergistically Enhances the Open-Circuit Voltage and Quantum Efficiency of Photovoltaic Solar-Blind Ultraviolet Detectors.

Increasing the open-circuit voltage (VOC) is of a great significance to achieve high photoelectric conversion efficiency in photovoltaic applications. Here, we present a simple NO2 doping strategy that can significantly modulate the VOC of graphene-based solar-blind ultraviolet photodetectors from 0.96 to 1.84 V. The intriguing result can be demonstrated by the fact that NO2 doping lowers the Fermi surface of graphene and thus enhances quasi-Fermi level splitting of the whole device under illumination. The >103% increase of both external quantum efficiency and photoresponsivity compared to before doping is the result of a 0.88 V increase in the VOC. Our work sheds light on the forming mechanism of VOC in graphene-based photovoltaic detectors and further suggests alternative pathways to enhance the VOC of photovoltaic devices with high efficiency.

Solar-blind field-assisted NEA AlGaN heterojunction nanocone array photocathode

With the abundant utilization of ultraviolet detectors, the proposal for designing vacuum photoelectron emitting devices with efficient solar blind detection performance continues to increase. To alleviate the phenomenon of “secondary absorption” where photoelectrons are absorbed by an adjacent nanocone, in general, nanocone arrays, the theoretical model of the field-assisted negative electron affinity Alx1Ga1−x1N/Alx2Ga1−x2N heterojunction nanocone array photocathode is established. The built-in electric field of the heterojunction nanocone directed from top to bottom is utilized to promote the drifting of photocurrent along the nanocone, and the external electric field induced by a silver electrode is expected to enhance the probability of electron collection. The results show that the electron collection ratio is enhanced and the electron collection efficiency of the nanocone photocathode is improved, which proves the effectiveness of the applied electric field. This work could turn into the theoretical guidance of the design and manufacture of high-performance solar-blind ultraviolet detectors.

Pt/(InGa)2O3/n-Si Heterojunction-Based Solar-Blind Ultraviolet Photovoltaic Detectors with an Ideal Absorption Cutoff Edge of 280 nm.

Ga2O3 is a popular material for research on solar-blind ultraviolet detectors. However, its absorption cutoff edge is 253 nm, which is not an ideal cutoff edge of 280 nm. In this work, by adjusting the ratio of In/Ga elements in the films, a high-quality (In0.11Ga0.89)2O3 film with an absorption cutoff edge of 280 nm was obtained, which owns a uniform surface and preferred orientation. On this basis, a solar-blind ultraviolet photovoltaic detector was constructed based on the Pt/(In0.11Ga0.89)2O3/n-Si heterojunction. When the device is exposed to 254 nm UV light, its open-circuit voltage (VOC) can reach 354 mV. Under 0 V bias, the device has a responsivity of 0.48 mA/W with a rise time of 0.47 s and a decay time of 0.37 s; under -7 V bias, the device achieves a responsivity of 16.96 mA/W with a rise time of 0.17 s and a decay time of 0.33 s. The spectral response characteristics of the device show that it has a selective response to solar-blind ultraviolet light (cutoff wavelength is 280 nm) with a rejection ratio (R254 nm/R310 nm), which is greater by more than two orders of magnitude. This work provides a good reference for adjusting the band gap of Ga2O3-based films and broadening their application fields.

Multiple-quantum-well-induced unipolar carrier transport multiplication in AlGaN solar-blind ultraviolet photodiode

AlGaN solar-blind ultraviolet (SBUV) detectors have potential application in fire monitoring, corona discharge monitoring, or biological imaging. With the promotion of application requirements, there is an urgent demand for developing a high-performance vertical detector that can work at low bias or even zero bias. In this work, we have introduced a photoconductive gain mechanism into a vertical AlGaN SBUV detector and successfully realized it in a p - i - n photodiode via inserting a multiple-quantum-well (MQW) into the depletion region. The MQW plays the role of trapping holes and increasing carrier lifetime due to its strong hole confinement effect and quantum confinement Stark effect. Hence, the electrons can go through the detector multiple times, inducing unipolar carrier transport multiplication. Experimentally, an AlGaN SBUV detector with a zero-bias peak responsivity of about 0.425 A/W at 233 nm is achieved, corresponding to an external quantum efficiency of 226%, indicating the existence of internal current gain. When compared with the device without MQW structure, the gain is estimated to be about 10 3 in magnitude. The investigation provides an alternative and effective approach to obtain high current gain in vertical AlGaN SBUV detectors at zero bias.

Performance enhancement of a self-powered solar-blind UV photodetector based on ZnGa2O4/Si heterojunction via interface pyroelectric effect

The photodetectors based on the wide bandgap semiconductor (WBS)/Si heterojunction have attracted more and more attention in recent years due to their excellent photoelectric characteristics and easy integration capabilities. In this work, we have demonstrated a self-powered solar-blind ultraviolet (UV) photodetector based on the ZnGa2O4/Si heterojunction. A typical rectification characteristic with a rectification ratio exceeding 103 within ±5 V can be obtained. At 0 V bias, the −3 dB cutoff wavelength of ∼255 nm and the UV-visible rejection ratio of ∼3 × 102 show that the device has excellent self-powered solar-blind UV detection performance. In addition, the responsivity and the response speed of ZnGa2O4/Si heterojunction can be efficiently enhanced by a transient spike current at 0 V bias when turning on and off the 254 nm UV light. The interface pyroelectric effect of the ZnGa2O4 film should be responsible for this transient spike photocurrent phenomenon. Our findings in this work pave a feasible way to realize high-performance WBS/Si heterojunction self-powered solar-blind photodetectors.

Resonance absorption and quantum efficiency of graded composition AlxGa1-xN nanowire array cathode

In order to fully utilize the energy of sunlight as much as possible, nanowire array (NWA) photocathodes have begun to be explored. The photoemission capability of the graded composition AlxGa1-xN NWA was studied to solve the problem of “secondary absorption” of escaping electrons by the adjacent nanowires of the NWA photocathode. The results show that the built-in electric field introduced by the graded composition can promote the drift and diffusion of the carriers inside the nanowire to the top surface. The single-component Al0.49Ga0.51N NWA is obtained the highest quantum efficiency at a resonance wavelength of 347 nm, which is approximately 42.81%. However, the graded composition AlxGa1-xN NWA cathode can obtain a quantum efficiency of 62.32% at 274 nm, which not only achieves an increase in quantum efficiency, but also causes a blue shift in the resonance wavelength. Furthermore, the graded composition AlxGa1-xN NWA cathode with a uniform thickness of H = 700 nm, P = 300 nm, and D = 150 nm has a resonance absorption of about 98% and a reflectance of only 1% at the resonance wavelength. The above studies all show that the graded composition AlxGa1-xN NWA cathode can be used as a future candidate core device for vacuum solar blind ultraviolet detectors.

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.

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.

Polarization-enhanced AlGaN solar-blind ultraviolet detectors

AlGaN solar-blind ultraviolet detectors have great potential in many fields, although their performance has not fully meet the requirements until now. Here, we proposed an approach to utilize the inherent polarization effect of AlGaN to improve the detector performance. AlGaN heterostructures were designed to enhance the polarization field in the absorption layer, and a high built-in field and a high electron mobility conduction channel were formed. As a result, a high-performance solar-blind ultraviolet detector with a peak responsivity of 1.42 A/W at 10 V was achieved, being 50 times higher than that of the nonpolarization-enhanced one. Moreover, an electron reservoir structure was proposed to further improve the performance. A higher peak responsivity of 3.1 A/W at 30 V was achieved because the electron reservoir structure could modulate the electron concentration in the conduction channel. The investigation presented here provided feasible approaches to improve the performance of the AlGaN detector by taking advantage of its inherent property.

Performance improvement of amorphous Ga2O3 ultraviolet photodetector by annealing under oxygen atmosphere

We have demonstrated the fast-speed and high-rejection-ratio solar-blind ultraviolet (UV) photodetectors based on amorphous Ga2O3 (a-Ga2O3) films grown by atomic layer deposition. The effect of the annealing under oxygen atmosphere on the performance of a-Ga2O3 photodetectors is investigated. By the oxygen annealing at 500 °C, the 90-10% decay time of a-Ga2O3 photodetector can be decreased to ∼150 ns, and the UV/Visible rejection ratio of the photodetector can reach as high as 2.74×105, due to the significant suppression of the visible light response. Moreover, the dark current of the 500 °C-annealed photodetector is only 9.43 pA at 10 V bias. These phenomena can be explained by the decrease in oxygen vacancy concentration of the a-Ga2O3 films after the oxygen annealing. The combination of high rejection ratios and fast operating speeds offers a viable way for facile and scalable fabrication of the oxide semiconductor solar-blind UV detectors.