The AlGaN-based deep ultraviolet light-emitting diodes（LED） with double electron blocking layers（d-EBLs） on both sides of the active region are investigated theoretically. They possess many excellent performances ...The AlGaN-based deep ultraviolet light-emitting diodes（LED） with double electron blocking layers（d-EBLs） on both sides of the active region are investigated theoretically. They possess many excellent performances compared with the conventional structure with only a single electron blocking layer, such as a higher recombination rate, improved light output power and internal quantum efficiency（IQE）. The reasons can be concluded as follows. On the one hand, the weakened electrostatic field within the quantum wells（QWs） enhances the electron–hole spatial overlap in QWs, and therefore increases the probability of radioactive recombination. On the other hand, the added n-AlGaN layer can not only prevent holes from overflowing into the n-side region but also act as another electron source, providing more electrons.展开更多
AlGaN-based ultraviolet light-emitting diodes(UV-LEDs) have attracted considerable interest due to their wide range of application fields. However, they are still suffering from low light out power and unsatisfactory ...AlGaN-based ultraviolet light-emitting diodes(UV-LEDs) have attracted considerable interest due to their wide range of application fields. However, they are still suffering from low light out power and unsatisfactory quantum efficiency.The utilization of polarization-doped technique by grading the Al content in p-type layer has demonstrated its effectiveness in improving LED performances by providing sufficiently high hole concentration. However, too large degree of grading through monotonously increasing the Al content causes strains in active regions, which constrains application of this technique, especially for short wavelength UV-LEDs. To further improve 340-nm UV-LED performances, segmentally graded Al content p-Al_xGa_(1-x)N has been proposed and investigated in this work. Numerical results show that the internal quantum efficiency and output power of proposed structures are improved due to the enhanced carrier concentrations and radiative recombination rate in multiple quantum wells, compared to those of the conventional UV-LED with a stationary Al content AlGaN electron blocking layer. Moreover, by adopting the segmentally graded p-Al_xGa_(1-x)N, band bending within the last quantum barrier/p-type layer interface is effectively eliminated.展开更多
The transport mechanisms of the reverse leakage current in the UV light-emitting diodes （380nm） are investi- gated by the temperature-dependent current-voltage measurement first. Three possible transport mechanisms,...The transport mechanisms of the reverse leakage current in the UV light-emitting diodes （380nm） are investi- gated by the temperature-dependent current-voltage measurement first. Three possible transport mechanisms, the space-limited-charge conduction, the variable-range hopping and the Poole-Frenkel emission, are proposed to explain the transport process of the reverse leakage current above 295 K, respectively. With the in-depth investigation, the former two transport mechanisms are excluded. It is found that the experimental data agree well with the Poole Frenkel emission model. Furthermore, the activation energies of the traps that cause the reverse leakage current are extracted, which are 0.05eV, 0.09eV, and 0.11 eV, respectively. This indicates that at least three types of trap states are located below the bottom of the conduction band in the depletion region of the UV LEDs.展开更多
The conventional stationary Al content Al GaN electron blocking layer(EBL) in ultraviolet light-emitting diode(UV LED) is optimized by employing a linearly graded Al Ga N inserting layer which is 2.0 nm Al_(0.3) Ga_(0...The conventional stationary Al content Al GaN electron blocking layer(EBL) in ultraviolet light-emitting diode(UV LED) is optimized by employing a linearly graded Al Ga N inserting layer which is 2.0 nm Al_(0.3) Ga_(0.7) N/5.0 nm Alx Ga_(1-x) N/8.0 nm Al_(0.3) Ga_(0.7) N with decreasing value of x. The results indicate that the internal quantum efficiency is significantly improved and the efficiency droop is mitigated by using the proposed structure. These improvements are attributed to the increase of the effective barrier height for electrons and the reduction of the effective barrier height for holes,which result in an increased hole injection efficiency and a decreased electron leakage into the p-type region. In addition,the linearly graded AlGaN inserting layer can generate more holes in EBL due to the polarization-induced hole doping and a tunneling effect probably occurs to enhance the hole transportation to the active regions, which will be beneficial to the radiative recombination.展开更多
Background:The usage of the light emitting diode(LED)has been increasingly applied in the illumination setting and electronic equipment.However,the effect of LED lights on the retina remains unclear.In this study,we o...Background:The usage of the light emitting diode(LED)has been increasingly applied in the illumination setting and electronic equipment.However,the effect of LED lights on the retina remains unclear.In this study,we observed and analyzed the impact of white LED lights at different intensities on the function and morphology of rat retinas.Methods:Thirty-six Sprague-Dawley rats weighing 150-180 g were randomly divided into six groups(n=6 in each group)including a normal control(NC)group,4 white LED groups at different light intensities(4,000,6,000,7,000,and 10,000 lux),and an ultraviolet B(UVB)lighting group(302 nm,1,000μw/cm2).After 24 hours of continuous illumination,full-field flash electroretinogram(FERG)and pathological examination were performed in each group.Results:As revealed by FERG,the impairment of retinal function gradually worsened with the increase of LED light intensity.In contrast,the UVB group had the most severe retinal function impairment.Particularly,the functional damage of rod cells and inner nuclear layer cells was the main FERG finding in each group.In the NC group,the retina had typical morphologies featured by well-defined structures,clearly visible border between the inner and outer segments,and neatly arranged inner and outer nuclear layer cells.After 24 hours of illumination,the inner and outer parts of the retina in the 4,000 lux group were still neatly arranged,along with a clear border;however,the inner and outer nuclear layers were randomly arranged,and some irregular nuclei and cells were lost.The damage of the internal and external retinal segments and the internal and external nuclear layers became more evident in the 6,000 lux group,7,000 lux group,and 10,000 lux group.The UVB group had a more obviously disordered arrangement of inner and outer nuclear layers and loss of cells.Conclusions:Continuous exposure to white LED light can cause structural and functional damage to rat retinas,and such damage is related to the intensity of illumination.Therefore,the risk of retinal damage should be considered during LED illumination,and proper LED illumination intensity may help to maintain eye health.展开更多
Vertical SnO_(2)based p-n junctions are pivotal since they built the core components in photoelectronic systems.Nevertheless,preparation of high-quality p-SnO_(2)with controllable hole mobility and concentration is st...Vertical SnO_(2)based p-n junctions are pivotal since they built the core components in photoelectronic systems.Nevertheless,preparation of high-quality p-SnO_(2)with controllable hole mobility and concentration is still a great challenge owing to the self-compensating effect and lattice distortion caused by the radius discrepancy between host and doped atoms.Herein,p type GaN:Mg grown by metal organic chemical vapor deposition is employed as hole transportation layer to construct p-n heterojunction with intrinsic n-SnO_(2)prepared by atomic layer deposition.Both material preparation techniques are compatible with current industrial mass production processes.The p-GaN/n-SnO_(2)heterojunction can be developed as solar cell,dual-color light emitting diode and self-powered,high speed ultraviolet(UV)photodetector with external quantum efficiency of 74%at 0 V bias voltage.In addition,direct recombination of donor bound excitons(D0 X)and UV emission red shifts caused by quantum confinement Stack effect are observed in SnO_(2).Since our device fabrication technique is a standard craft in photoelectronics,the study of p-GaN/n-SnO_(2)heterojunction suggests a simple and effective strategy for large scale device integration in next generation high performance photoelectronic devices.展开更多
Gafchromic external beam therapy 3(EBT3)film has widely been used in medical field applications.Principally,the EBT3 film’s color gradually changes from light green to darker color under incremental exposures by ioni...Gafchromic external beam therapy 3(EBT3)film has widely been used in medical field applications.Principally,the EBT3 film’s color gradually changes from light green to darker color under incremental exposures by ionizing or even non-ionizing ultraviolet(UV)radiation.Peak absorbance of the EBT3 film can be used to predict absorbed doses by the film.However,until today,related researches still rely on spectrometers for color analysis of EBT3 films.Hence,this paper presents a comparative analysis between results produced by the spectrometer and a much simpler light-emitting diode-photodiode based system in profiling the color changes of EBT3 films after exposure by solar UV radiation.This work has been conducted on a set of 50 EBT3 samples with incremental solar UV exposure(doses).The wavelength in the red region has the best sensitivity in profiling the color changes of EBT3 films for low solar UV exposure measurement.This study foresees the ability of blue wavelength to profile films with a large range of solar UV exposure.The LED(light emitting diode)-based optical system has produced comparable measurement accuracies to the spectrometer and thus,with a potential for replacing the need for a multipurpose spectroscopy system for simple measurement of light attenuation.展开更多
With their advantages of high efficiency,long lifetime,compact size and being free of mercury,ultraviolet light-emitting diodes(UV LEDs)are widely applied in disinfection and purification,photolithography,curing and b...With their advantages of high efficiency,long lifetime,compact size and being free of mercury,ultraviolet light-emitting diodes(UV LEDs)are widely applied in disinfection and purification,photolithography,curing and biomedical devices.However,it is challenging to assess the reliability of UV LEDs based on the traditional life test or even the accelerated life test.In this paper,radiation power degradation modeling is proposed to estimate the lifetime of UV LEDs under both constant stress and step stress degradation tests.Stochastic data-driven predic-tions with both Gamma process and Wiener process methods are implemented,and the degradation mechanisms occurring under different aging conditions are also analyzed.The results show that,compared to least squares regression in the IESNA TM-21 industry standard recommended by the Illuminating Engineering Society of North America(IESNA),the proposed stochastic data-driven methods can predict the lifetime with high accuracy and narrow confidence intervals,which confirms that they provide more reliable information than the IESNA TM-21 standard with greater robustness.展开更多
The objective of this work is to simulate a single quantum well ultraviolet light emitting diode(LED) based on AlGaN/GaN/AlGaN and AlGaN/BGaN/AlGaN, by using TCAD Silvaco simulator. The first structure has a GaN quant...The objective of this work is to simulate a single quantum well ultraviolet light emitting diode(LED) based on AlGaN/GaN/AlGaN and AlGaN/BGaN/AlGaN, by using TCAD Silvaco simulator. The first structure has a GaN quantum well taken between two layers, of n-AlGaN and p-AlGaN. The second one has a BGaN quantum well instead of GaN. We fix the concentration of the boron in BGaN to only 1% and we vary the thickness of GaN and BGaN quantum well layer from 7 to 20 nm, for the two structures. As results, we obtain respectively for GaN-LED and BGaN-LED, a maximum current of 0.52 and 0.27 mA, a maximum power spectral density of 1.935 and 6.7 W cm^(-1) eV^(-1), a maximum spontaneous emission of 3.34 × 10^(28) and 3.43 × 10^(28) s^(-1) cm^(-3) eV^(-1), and a maximum Light output power of 0.56 and 0.89 mW.展开更多
基金Project supported by the Special Strategic Emerging Industries of Guangdong Province,China(Grant No.2012A080304006)the Major Scientific and Technological Projects of Zhongshan City,Guangdong Province,China(Grant No.2014A2FC204)the Forefront of Technology Innovation and Key Technology Projects of Guangdong Province,China(Grant Nos.2014B010121001 and 2014B010119004)
文摘The AlGaN-based deep ultraviolet light-emitting diodes（LED） with double electron blocking layers（d-EBLs） on both sides of the active region are investigated theoretically. They possess many excellent performances compared with the conventional structure with only a single electron blocking layer, such as a higher recombination rate, improved light output power and internal quantum efficiency（IQE）. The reasons can be concluded as follows. On the one hand, the weakened electrostatic field within the quantum wells（QWs） enhances the electron–hole spatial overlap in QWs, and therefore increases the probability of radioactive recombination. On the other hand, the added n-AlGaN layer can not only prevent holes from overflowing into the n-side region but also act as another electron source, providing more electrons.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61874161 and 11474105)the Science and Technology Program of Guangdong Province,China(Grant Nos.2017B010127001 and 2015B010105011)+4 种基金the Education Department Project of Guangdong Province,China(Grant No.2017KZDXM022)the Science and Technology Project of Guangzhou City,China(Grant No.201607010246)the Program for Changjiang Scholars and Innovative Research Team in Universities of China(Grant No.IRT13064)the Science and Technology Project of Shenzhen City,China(Grant No.GJHZ20180416164721073)the Science and Technology Planning of Guangdong Province,China(Grant No.2015B010112002)
文摘AlGaN-based ultraviolet light-emitting diodes(UV-LEDs) have attracted considerable interest due to their wide range of application fields. However, they are still suffering from low light out power and unsatisfactory quantum efficiency.The utilization of polarization-doped technique by grading the Al content in p-type layer has demonstrated its effectiveness in improving LED performances by providing sufficiently high hole concentration. However, too large degree of grading through monotonously increasing the Al content causes strains in active regions, which constrains application of this technique, especially for short wavelength UV-LEDs. To further improve 340-nm UV-LED performances, segmentally graded Al content p-Al_xGa_(1-x)N has been proposed and investigated in this work. Numerical results show that the internal quantum efficiency and output power of proposed structures are improved due to the enhanced carrier concentrations and radiative recombination rate in multiple quantum wells, compared to those of the conventional UV-LED with a stationary Al content AlGaN electron blocking layer. Moreover, by adopting the segmentally graded p-Al_xGa_(1-x)N, band bending within the last quantum barrier/p-type layer interface is effectively eliminated.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61334002,61474091,61404097,61574110and 61574112the 111 Project of China under Grant No B12026the Scientific Research Foundation for the Returned Overseas Chinese Scholars of State Education Ministry of China under Grant No JY0600132501
文摘The transport mechanisms of the reverse leakage current in the UV light-emitting diodes （380nm） are investi- gated by the temperature-dependent current-voltage measurement first. Three possible transport mechanisms, the space-limited-charge conduction, the variable-range hopping and the Poole-Frenkel emission, are proposed to explain the transport process of the reverse leakage current above 295 K, respectively. With the in-depth investigation, the former two transport mechanisms are excluded. It is found that the experimental data agree well with the Poole Frenkel emission model. Furthermore, the activation energies of the traps that cause the reverse leakage current are extracted, which are 0.05eV, 0.09eV, and 0.11 eV, respectively. This indicates that at least three types of trap states are located below the bottom of the conduction band in the depletion region of the UV LEDs.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61874161 and 11474105)the Science and Technology Program of Guangdong Province,China(Grant No.2017B010127001)+1 种基金the Science and Technology of Shenzhen City,China(Grant No.GJHZ20180416164721073)the Education Department Funding of Guangdong Province,China(Grant No.2017KZDXM022)
文摘The conventional stationary Al content Al GaN electron blocking layer(EBL) in ultraviolet light-emitting diode(UV LED) is optimized by employing a linearly graded Al Ga N inserting layer which is 2.0 nm Al_(0.3) Ga_(0.7) N/5.0 nm Alx Ga_(1-x) N/8.0 nm Al_(0.3) Ga_(0.7) N with decreasing value of x. The results indicate that the internal quantum efficiency is significantly improved and the efficiency droop is mitigated by using the proposed structure. These improvements are attributed to the increase of the effective barrier height for electrons and the reduction of the effective barrier height for holes,which result in an increased hole injection efficiency and a decreased electron leakage into the p-type region. In addition,the linearly graded AlGaN inserting layer can generate more holes in EBL due to the polarization-induced hole doping and a tunneling effect probably occurs to enhance the hole transportation to the active regions, which will be beneficial to the radiative recombination.
基金Supported by the Guangdong Natural Science Foundation(2016A030313294).
文摘Background:The usage of the light emitting diode(LED)has been increasingly applied in the illumination setting and electronic equipment.However,the effect of LED lights on the retina remains unclear.In this study,we observed and analyzed the impact of white LED lights at different intensities on the function and morphology of rat retinas.Methods:Thirty-six Sprague-Dawley rats weighing 150-180 g were randomly divided into six groups(n=6 in each group)including a normal control(NC)group,4 white LED groups at different light intensities(4,000,6,000,7,000,and 10,000 lux),and an ultraviolet B(UVB)lighting group(302 nm,1,000μw/cm2).After 24 hours of continuous illumination,full-field flash electroretinogram(FERG)and pathological examination were performed in each group.Results:As revealed by FERG,the impairment of retinal function gradually worsened with the increase of LED light intensity.In contrast,the UVB group had the most severe retinal function impairment.Particularly,the functional damage of rod cells and inner nuclear layer cells was the main FERG finding in each group.In the NC group,the retina had typical morphologies featured by well-defined structures,clearly visible border between the inner and outer segments,and neatly arranged inner and outer nuclear layer cells.After 24 hours of illumination,the inner and outer parts of the retina in the 4,000 lux group were still neatly arranged,along with a clear border;however,the inner and outer nuclear layers were randomly arranged,and some irregular nuclei and cells were lost.The damage of the internal and external retinal segments and the internal and external nuclear layers became more evident in the 6,000 lux group,7,000 lux group,and 10,000 lux group.The UVB group had a more obviously disordered arrangement of inner and outer nuclear layers and loss of cells.Conclusions:Continuous exposure to white LED light can cause structural and functional damage to rat retinas,and such damage is related to the intensity of illumination.Therefore,the risk of retinal damage should be considered during LED illumination,and proper LED illumination intensity may help to maintain eye health.
基金National Natural Science Foundation of China,Grant/Award Number:No.61705043Natural Science Foundation of Jiangsu Province,Grant/Award Number:No.BK20160568+1 种基金Science and Technology Commission of Shanghai Municipality,Shanghai Sailing Program,Grant/Award Number:No.19YF1433300Startup Fund of ShanghaiTech University。
文摘Vertical SnO_(2)based p-n junctions are pivotal since they built the core components in photoelectronic systems.Nevertheless,preparation of high-quality p-SnO_(2)with controllable hole mobility and concentration is still a great challenge owing to the self-compensating effect and lattice distortion caused by the radius discrepancy between host and doped atoms.Herein,p type GaN:Mg grown by metal organic chemical vapor deposition is employed as hole transportation layer to construct p-n heterojunction with intrinsic n-SnO_(2)prepared by atomic layer deposition.Both material preparation techniques are compatible with current industrial mass production processes.The p-GaN/n-SnO_(2)heterojunction can be developed as solar cell,dual-color light emitting diode and self-powered,high speed ultraviolet(UV)photodetector with external quantum efficiency of 74%at 0 V bias voltage.In addition,direct recombination of donor bound excitons(D0 X)and UV emission red shifts caused by quantum confinement Stack effect are observed in SnO_(2).Since our device fabrication technique is a standard craft in photoelectronics,the study of p-GaN/n-SnO_(2)heterojunction suggests a simple and effective strategy for large scale device integration in next generation high performance photoelectronic devices.
基金This work was financially supported by the Ministry of Higher Education Malaysia-Fundamental Research Grant Scheme(Grant No.203/PFIZIK/6711491).
文摘Gafchromic external beam therapy 3(EBT3)film has widely been used in medical field applications.Principally,the EBT3 film’s color gradually changes from light green to darker color under incremental exposures by ionizing or even non-ionizing ultraviolet(UV)radiation.Peak absorbance of the EBT3 film can be used to predict absorbed doses by the film.However,until today,related researches still rely on spectrometers for color analysis of EBT3 films.Hence,this paper presents a comparative analysis between results produced by the spectrometer and a much simpler light-emitting diode-photodiode based system in profiling the color changes of EBT3 films after exposure by solar UV radiation.This work has been conducted on a set of 50 EBT3 samples with incremental solar UV exposure(doses).The wavelength in the red region has the best sensitivity in profiling the color changes of EBT3 films for low solar UV exposure measurement.This study foresees the ability of blue wavelength to profile films with a large range of solar UV exposure.The LED(light emitting diode)-based optical system has produced comparable measurement accuracies to the spectrometer and thus,with a potential for replacing the need for a multipurpose spectroscopy system for simple measurement of light attenuation.
基金The work described in this paper was partially supported by the National Natural Science Foundation of China(51805147)Shang-hai Science and Technology Development Funds(19DZ2253400)+1 种基金the Six Talent Peaks Project in Jiangsu Province(GDZB-017)the Fundamental Research Funds for the Central Universities(B200203031).
文摘With their advantages of high efficiency,long lifetime,compact size and being free of mercury,ultraviolet light-emitting diodes(UV LEDs)are widely applied in disinfection and purification,photolithography,curing and biomedical devices.However,it is challenging to assess the reliability of UV LEDs based on the traditional life test or even the accelerated life test.In this paper,radiation power degradation modeling is proposed to estimate the lifetime of UV LEDs under both constant stress and step stress degradation tests.Stochastic data-driven predic-tions with both Gamma process and Wiener process methods are implemented,and the degradation mechanisms occurring under different aging conditions are also analyzed.The results show that,compared to least squares regression in the IESNA TM-21 industry standard recommended by the Illuminating Engineering Society of North America(IESNA),the proposed stochastic data-driven methods can predict the lifetime with high accuracy and narrow confidence intervals,which confirms that they provide more reliable information than the IESNA TM-21 standard with greater robustness.
基金supported by the University of Abou-Bekr-Belkaid, Materials and Renewable Energy Research Unit, Tlemcen, Algeria
文摘The objective of this work is to simulate a single quantum well ultraviolet light emitting diode(LED) based on AlGaN/GaN/AlGaN and AlGaN/BGaN/AlGaN, by using TCAD Silvaco simulator. The first structure has a GaN quantum well taken between two layers, of n-AlGaN and p-AlGaN. The second one has a BGaN quantum well instead of GaN. We fix the concentration of the boron in BGaN to only 1% and we vary the thickness of GaN and BGaN quantum well layer from 7 to 20 nm, for the two structures. As results, we obtain respectively for GaN-LED and BGaN-LED, a maximum current of 0.52 and 0.27 mA, a maximum power spectral density of 1.935 and 6.7 W cm^(-1) eV^(-1), a maximum spontaneous emission of 3.34 × 10^(28) and 3.43 × 10^(28) s^(-1) cm^(-3) eV^(-1), and a maximum Light output power of 0.56 and 0.89 mW.
