The optical polarization characteristics of surface plasmon(SP)coupled Al Ga N-based light emitting diodes(LEDs)are investigated theoretically by analyzing the radiation recombination process and scattering process re...The optical polarization characteristics of surface plasmon(SP)coupled Al Ga N-based light emitting diodes(LEDs)are investigated theoretically by analyzing the radiation recombination process and scattering process respectively.For the Al_(0.5)Ga_(0.5)N/Al/Al_(2)O_(3)slab structure,the relative intensity of TE-polarized and TM-polarized spontaneous emission(SE)rate into the SP mode obviously depends on the thickness of the Al layer.The calculation results show that TM dominated emission will be transformed into TE dominated emission with the decrease of the Al thickness,while the emission intensities of both TE/TM polarizations will decrease significantly.In addition,compared with TM polarized emission,TE polarized emission is easier to be extracted by SP coupling.For the Al_(0.5)Ga_(0.5)N/Al nano-particle structure,the ratio of transmittance for TE/TM polarized emission can reach~3.06,while for the Al free structure,it is only 1.2.Thus,the degree of polarization of SP coupled LED can be improved by the reasonable structural design.展开更多
This paper reviews and introduces the techniques for boosting the light-extraction efficiency(LEE) of AlGaNbased deep-ultraviolet(DUV: λ < 300 nm) light-emitting diodes(LEDs) on the basis of the discussion of thei...This paper reviews and introduces the techniques for boosting the light-extraction efficiency(LEE) of AlGaNbased deep-ultraviolet(DUV: λ < 300 nm) light-emitting diodes(LEDs) on the basis of the discussion of their molecular structures and optical characteristics, focusing on organoencapsulation materials. Comparisons of various fluororesins, silicone resin, and nonorgano materials are described. The only usable organomaterial for encapsulating DUV-LEDs is currently considered to be polymerized perfluoro(4-vinyloxy-1-butene)(p-BVE)terminated with a —CF3 end group. By forming hemispherical lenses on DUV-LED dies using p-BVE having a —CF3 end group with a refractive index of about 1.35, the LEE was improved by 1.5-fold, demonstrating a cost-feasible packaging technique.展开更多
AlGaN-based materials have exhibited considerable potential for fabricating ultraviolet(UV)light-emitting diodes(LEDs)owing to their direct,wide,and adjustable energy bandgap.AlGaN-based devices have extensive appli-c...AlGaN-based materials have exhibited considerable potential for fabricating ultraviolet(UV)light-emitting diodes(LEDs)owing to their direct,wide,and adjustable energy bandgap.AlGaN-based devices have extensive appli-cability owing to their stable physico-chemical properties.With decades of research effort,significant progress has been achieved in enhancing the working efficiency of AlGaN-based LEDs by optimizing the crystalline qual-ity,doping efficiency,and device design.In this review,methods to obtain high-quality AlGaN-based materials,achieve high doping efficiency,and design UV-LED structures are summarized and discussed.Finally,the issues that need to be addressed in AlGaN-based UV-LED devices are highlighted.展开更多
This paper reports a comprehensive analysis of the origin of the electroluminescence(EL)peaks and of the thermal droop in UV-B AlGaN-based LEDs.By carrying out spectral measurements at several temperatures and current...This paper reports a comprehensive analysis of the origin of the electroluminescence(EL)peaks and of the thermal droop in UV-B AlGaN-based LEDs.By carrying out spectral measurements at several temperatures and currents,(i)we extract information on the physical origin of the various spectral bands,and(ii) we develop a novel closed-form model based on the Shockley–Read–Hall theory and on the ABC rate equation that is able to reproduce the experimental data on thermal droop caused by non-radiative recombination through deep levels.In the samples under test,the three EL bands are ascribed to the following processes:band-to-band recombination in the quantum wells(main EL peak),a parasitic intra-bandgap radiative transition in the quantum well barriers,and a second defect-related radiative process in the p-AlGaN superlattice.展开更多
We report on AlGaN-based tunnel heterojunctions grown by metalorganic vapor phase epitaxy enabling fully transparent UVC LEDs by eliminating the absorbing p-AlGaN and p-GaN layers. Furthermore, the electrical characte...We report on AlGaN-based tunnel heterojunctions grown by metalorganic vapor phase epitaxy enabling fully transparent UVC LEDs by eliminating the absorbing p-AlGaN and p-GaN layers. Furthermore, the electrical characteristics can be improved by exploiting the higher conductivity of n-AlGaN layers as well as a lower resistance of n-contacts. UVC LEDs with AlGaN:Mg/AlGaN:Si tunnel junctions exhibiting single peak emission at268 nm have been realized, demonstrating effective carrier injection into the AlGaN multiple quantum well active region. The incorporation of a low band gap interlayer enables effective tunneling and strong voltage reduction.Therefore, the interlayer thickness is systematically varied. Tunnel heterojunction LEDs with an 8 nm thick GaN interlayer exhibit continuous-wave emission powers >3 m W near thermal rollover. External quantum efficiencies of 1.4% at a DC current of 5 m A and operating voltages of 20 V are measured on-wafer. Laterally homogeneous emission is demonstrated by UV-sensitive electroluminescence microscopy images. The complete UVC LED heterostructure is grown in a single epitaxy process including in situ activation of the magnesium acceptors.展开更多
The development of semiconductors is always accompanied by the progress in controllable doping techniques.Taking AlGaN-based ultraviolet(UV)emitters as an example,despite a peak wall-plug efficiency of 15.3%at the wav...The development of semiconductors is always accompanied by the progress in controllable doping techniques.Taking AlGaN-based ultraviolet(UV)emitters as an example,despite a peak wall-plug efficiency of 15.3%at the wavelength of 275 nm,there is still a huge gap in comparison with GaN-based visible light-emitting diodes(LEDs),mainly attributed to the inefficient doping of AlGaN with increase of the Al composition.First,p-doping of Al-rich AlGaN is a long-standing challenge and the low hole concentration seriously restricts the carrier injection efficiency.Although p-GaN cladding layers are widely adopted as a compromise,the high injection barrier of holes as well as the inevitable loss of light extraction cannot be neglected.While in terms of n-doping the main issue is the degradation of the electrical property when the Al composition exceeds 80%,resulting in a low electrical efficiency in sub-250 nm UV-LEDs.This review summarizes the recent advances and outlines the major challenges in the efficient doping of Al-rich AlGaN,meanwhile the corresponding approaches pursued to overcome the doping issues are discussed in detail.展开更多
基金the National Nature Science Foundation of China(Grant Nos.62004109,61874168,and 62074086)Jiangsu Provincial Double-Innovation Doctor Program,Development of antibacterial multifunctional PVC facing new material technology(Grant No.21ZH626)。
文摘The optical polarization characteristics of surface plasmon(SP)coupled Al Ga N-based light emitting diodes(LEDs)are investigated theoretically by analyzing the radiation recombination process and scattering process respectively.For the Al_(0.5)Ga_(0.5)N/Al/Al_(2)O_(3)slab structure,the relative intensity of TE-polarized and TM-polarized spontaneous emission(SE)rate into the SP mode obviously depends on the thickness of the Al layer.The calculation results show that TM dominated emission will be transformed into TE dominated emission with the decrease of the Al thickness,while the emission intensities of both TE/TM polarizations will decrease significantly.In addition,compared with TM polarized emission,TE polarized emission is easier to be extracted by SP coupling.For the Al_(0.5)Ga_(0.5)N/Al nano-particle structure,the ratio of transmittance for TE/TM polarized emission can reach~3.06,while for the Al free structure,it is only 1.2.Thus,the degree of polarization of SP coupled LED can be improved by the reasonable structural design.
文摘This paper reviews and introduces the techniques for boosting the light-extraction efficiency(LEE) of AlGaNbased deep-ultraviolet(DUV: λ < 300 nm) light-emitting diodes(LEDs) on the basis of the discussion of their molecular structures and optical characteristics, focusing on organoencapsulation materials. Comparisons of various fluororesins, silicone resin, and nonorgano materials are described. The only usable organomaterial for encapsulating DUV-LEDs is currently considered to be polymerized perfluoro(4-vinyloxy-1-butene)(p-BVE)terminated with a —CF3 end group. By forming hemispherical lenses on DUV-LED dies using p-BVE having a —CF3 end group with a refractive index of about 1.35, the LEE was improved by 1.5-fold, demonstrating a cost-feasible packaging technique.
基金supported by the National Natural Science Foundation for Distinguished Young Scholars of China(Grant No.61725403)the National Natural Science Foundation of China(Grants No.61922078,61874090 and 61974002)+4 种基金Key Research Program of CAS(Grant No.XDPB22)the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grants No.Y201945 and 2019222)the Key scien-tific and technological Program of Xiamen(Grant No.3502Z20191016)the Youth Talent Promotion Project of Chinese Institute of Electron-ics(Grant No.2020QNRC001)the Key-Area Research and Devel-opment Program of Suzhou Institute of Nano-Tech and Nano-Bionics(Grant No.20YZ10).
文摘AlGaN-based materials have exhibited considerable potential for fabricating ultraviolet(UV)light-emitting diodes(LEDs)owing to their direct,wide,and adjustable energy bandgap.AlGaN-based devices have extensive appli-cability owing to their stable physico-chemical properties.With decades of research effort,significant progress has been achieved in enhancing the working efficiency of AlGaN-based LEDs by optimizing the crystalline qual-ity,doping efficiency,and device design.In this review,methods to obtain high-quality AlGaN-based materials,achieve high doping efficiency,and design UV-LED structures are summarized and discussed.Finally,the issues that need to be addressed in AlGaN-based UV-LED devices are highlighted.
基金Bundesministerium fur Bildung und Forschung(BMBF)(03ZZ0105A,03ZZ0105B)Bundesministerium fur Wirtschaft und Energie(BMWi)(03EFCBE067)Deutsche Forschungsgemeinschaft(DFG)(CRC 787)
文摘This paper reports a comprehensive analysis of the origin of the electroluminescence(EL)peaks and of the thermal droop in UV-B AlGaN-based LEDs.By carrying out spectral measurements at several temperatures and currents,(i)we extract information on the physical origin of the various spectral bands,and(ii) we develop a novel closed-form model based on the Shockley–Read–Hall theory and on the ABC rate equation that is able to reproduce the experimental data on thermal droop caused by non-radiative recombination through deep levels.In the samples under test,the three EL bands are ascribed to the following processes:band-to-band recombination in the quantum wells(main EL peak),a parasitic intra-bandgap radiative transition in the quantum well barriers,and a second defect-related radiative process in the p-AlGaN superlattice.
基金Bundesministerium für Bildung und Forschung(BMBF)“Advanced UV for Life” Project(03ZZ0134C)Deutsche Forschungsgemeinschaft(DFG)Collaborative Research Centre “Semiconductor Nanophotonics”(CRC787 9315)
文摘We report on AlGaN-based tunnel heterojunctions grown by metalorganic vapor phase epitaxy enabling fully transparent UVC LEDs by eliminating the absorbing p-AlGaN and p-GaN layers. Furthermore, the electrical characteristics can be improved by exploiting the higher conductivity of n-AlGaN layers as well as a lower resistance of n-contacts. UVC LEDs with AlGaN:Mg/AlGaN:Si tunnel junctions exhibiting single peak emission at268 nm have been realized, demonstrating effective carrier injection into the AlGaN multiple quantum well active region. The incorporation of a low band gap interlayer enables effective tunneling and strong voltage reduction.Therefore, the interlayer thickness is systematically varied. Tunnel heterojunction LEDs with an 8 nm thick GaN interlayer exhibit continuous-wave emission powers >3 m W near thermal rollover. External quantum efficiencies of 1.4% at a DC current of 5 m A and operating voltages of 20 V are measured on-wafer. Laterally homogeneous emission is demonstrated by UV-sensitive electroluminescence microscopy images. The complete UVC LED heterostructure is grown in a single epitaxy process including in situ activation of the magnesium acceptors.
基金This work was supported by the National Key Research and Development Program of China(No.2022YFB3605100)the National Natural Science Foundation of China(Nos.62234001,61927806,61974002,62135013,and 62075081)+1 种基金the Key-Area Research and Development Program of Guangdong Province(No.2020B010172001)the Major Scientific and Technological Innovation Project(MSTIP)of Shandong Province(No.2019JZZY010209).
文摘The development of semiconductors is always accompanied by the progress in controllable doping techniques.Taking AlGaN-based ultraviolet(UV)emitters as an example,despite a peak wall-plug efficiency of 15.3%at the wavelength of 275 nm,there is still a huge gap in comparison with GaN-based visible light-emitting diodes(LEDs),mainly attributed to the inefficient doping of AlGaN with increase of the Al composition.First,p-doping of Al-rich AlGaN is a long-standing challenge and the low hole concentration seriously restricts the carrier injection efficiency.Although p-GaN cladding layers are widely adopted as a compromise,the high injection barrier of holes as well as the inevitable loss of light extraction cannot be neglected.While in terms of n-doping the main issue is the degradation of the electrical property when the Al composition exceeds 80%,resulting in a low electrical efficiency in sub-250 nm UV-LEDs.This review summarizes the recent advances and outlines the major challenges in the efficient doping of Al-rich AlGaN,meanwhile the corresponding approaches pursued to overcome the doping issues are discussed in detail.
