Although the 5G wireless network has made significant advances,it is not enough to accommodate the rapidly rising requirement for broader bandwidth in post-5G and 6G eras.As a result,emerging technologies in higher fr...Although the 5G wireless network has made significant advances,it is not enough to accommodate the rapidly rising requirement for broader bandwidth in post-5G and 6G eras.As a result,emerging technologies in higher frequencies including visible light communication(VLC),are becoming a hot topic.In particular,LED-based VLC is foreseen as a key enabler for achieving data rates at the Tb/s level in indoor scenarios using multi-color LED arrays with wavelength division multiplexing(WDM)technology.This paper proposes an optimized multi-color LED array chip for high-speed VLC systems.Its long-wavelength GaN-based LED units are remarkably enhanced by V-pit structure in their efficiency,especially in the“yellow gap”region,and it achieves significant improvement in data rate compared with earlier research.This work investigates the V-pit structure and tries to provide insight by introducing a new equivalent circuit model,which provides an explanation of the simulation and experiment results.In the final test using a laboratory communication system,the data rates of eight channels from short to long wavelength are 3.91 Gb/s,3.77 Gb/s,3.67 Gb/s,4.40 Gb/s,3.78 Gb/s,3.18 Gb/s,4.31 Gb/s,and 4.35 Gb/s(31.38 Gb/s in total),with advanced digital signal processing(DSP)techniques including digital equalization technique and bit-power loading discrete multitone(DMT)modulation format.展开更多
The optical properties of GaN-based blue light-emitting diodes(LEDs)are extremely important to study as these LEDs are utilized in a great many industries due to their excellent qualities,including high brightness,hig...The optical properties of GaN-based blue light-emitting diodes(LEDs)are extremely important to study as these LEDs are utilized in a great many industries due to their excellent qualities,including high brightness,high energy efficiency,low energy consumption,and rapid reaction time.In this paper,Silvaco TCAD simulation software is used to do two-dimensional modeling and simulation of a GaN-based blue single quantum well vertical structure LED,with an emphasis on varied forward voltages,In components in InGaN,and quantum well thickness.The volt-ampere characteristic curve is compared and evaluated,as well as the energy band structure,carrier concentration,radiation recombination efficiency,electroluminescence spectrum,and internal current density distribution.The results show that when the forward voltage is 3.5V and the thickness of the quantum well is constant,the luminescence spectrum will show a red shift with the increase of the In content in the quantum well,and the luminescence spectrum will also show a red shift when the thickness of the quantum well is increased.However,when the quantum well thickness and In component are kept constant,the luminescence spectrum appears a red shift with increasing forward voltage.展开更多
GaN-based yellow light-emitting diodes(LEDs) on Si substrates are aged at a direct current density of 50 A/cm^2 for500 h. After the aging process, it can be found that the LEDs have a stable electrical property but th...GaN-based yellow light-emitting diodes(LEDs) on Si substrates are aged at a direct current density of 50 A/cm^2 for500 h. After the aging process, it can be found that the LEDs have a stable electrical property but their light output power is decayed by 4.01% at 35 A/cm^2. Additionally, the aging mechanism of GaN-based yellow LED is analyzed. It is found that the decay of light output power may be attributed to the following two reasons: one is the increase of Shockley–Rrad–Hall recombination and the other is the change of the transport path of holes via V-pits after aging, which may induce the radiative recombination current to decrease. In this paper, not only the aging mechanism of GaN-based yellow LED is investigated, but also a new possible research direction in LED aging is given.展开更多
Progress with GaN-based light emitting diodes (LEDs) that incorporate nanostructures is reviewed, especially the re- cent achievements in our research group. Nano-patterned sapphire substrates have been used to grow...Progress with GaN-based light emitting diodes (LEDs) that incorporate nanostructures is reviewed, especially the re- cent achievements in our research group. Nano-patterned sapphire substrates have been used to grow an A1N template layer for deep-ultraviolet (DUV) LEDs. One efficient surface nano-texturing technology, hemisphere-cones-hybrid nanostruc- tures, was employed to enhance the extraction efficiency of InGaN flip-chip LEDs. Hexagonal nanopyramid GaN-based LEDs have been fabricated and show electrically driven color modification and phosphor-free white light emission because of the linearly increased quantum well width and indium incorporation from the shell to the core. Based on the nanostruc- tures, we have also fabricated surface plasmon-enhanced nanoporous GaN-based green LEDs using AAO membrane as a mask. Benefitting from the strong lateral SP coupling as well as good electrical protection by a passivation layer, the EL intensity of an SP-enhanced nanoporous LED was significantly enhanced by 380%. Furthermore, nanostructures have been used for the growth of GaN LEDs on amorphous substrates, the fabrication of stretchable LEDs, and for increasing the 3-dB modulation bandwidth for visible light communication.展开更多
GaN-based irregular multiple quantum well (IMQW) structures assembled two different types of QWs emitting complementary wavelengths for dichromatic white light-emitting diodes (LEDs) are optimized in order to obta...GaN-based irregular multiple quantum well (IMQW) structures assembled two different types of QWs emitting complementary wavelengths for dichromatic white light-emitting diodes (LEDs) are optimized in order to obtain near white light emissions. The hole distributions and spontaneous emission spectra of the IMQW structures are analysed in detail by fully considering the effects of strain, well-coupling, valence band-mixing and polarization effect through employing a newly developed theoretical model from the k. p theory. Several structure parameters such as well material component, well width, layout of the wells and the thickness of harrier between different types of QWs are employed to analyse how these parameters together with the polarization effect influence the electronic and the optical properties of IMQW structure. Numerical results show that uniform hole distributions in different types of QWs are obtained when the number of the QWs emitting blue light is two, the number of the QWs emitting yellow light is one and the barrier between different types of QWs is 8nm in thickness. The near white light emission is realized using GaN-based IMQW structure with appropriate design parameters and injection level.展开更多
Design, fabrication and characterizations of GaN-based blue micro light emitting diode (LED) arrays are reported. The GaN micro-LED array consists of 320×256 pixels with a pitch size of 30μm. Each pixel is 25...Design, fabrication and characterizations of GaN-based blue micro light emitting diode (LED) arrays are reported. The GaN micro-LED array consists of 320×256 pixels with a pitch size of 30μm. Each pixel is 25×25μm^2 in size, which is designed for backside emission and high density flip-chip packaging. The selected LED pixels being tested exhibit good uniformity in terms of turn-on voltage and reverse leakage current. The efficiency droop behavior and reliability behavior under high forward current stress are also studied. The micro-LED pixel shows improved reliability, which is likely caused by enhanced heat dissipation.展开更多
GaN-based multiple quantum well light-emitting diodes (LEDs) with conventional and superlattice barriers have been investigated numerically. Simulation results demonstrate using InGaN/GaN superlattices as barriers c...GaN-based multiple quantum well light-emitting diodes (LEDs) with conventional and superlattice barriers have been investigated numerically. Simulation results demonstrate using InGaN/GaN superlattices as barriers can effectively enhance performances of the GaN-Based LEDs, mainly owing to the improvement of hole injection and transport among the MQW active region. Meanwhile, the improved electron capture decreases the electron leakage and alleviates the efficiency droop. The weak polarization field induced by the superlattice structure strengthens the intensity of the emission spectrum and leads to a blue-shift relative to the conventional one.展开更多
GaN/InGaN lighting-emitting diodes with different mesa structures are studied. The current-voltage characteristics, light output power, luminous efficiency, and peak wavelength of the GaN/InGaN lighting-emitting diode...GaN/InGaN lighting-emitting diodes with different mesa structures are studied. The current-voltage characteristics, light output power, luminous efficiency, and peak wavelength of the GaN/InGaN lighting-emitting diodes with different mesa patterns are compared. It shows that the current-voltage characteristics of the chips with more mesa areas are im- proved greatly by reducing the current crowding. With higher injection current the light output powers of GaN-based LED with more mesa areas are enhanced. And the chips with more P-electrode area have a smaller red shift and a little bit blue shift due to the reduction of the current crowding.展开更多
A correlation model between micro plasma noise and gamma irradiation of GaN-based LED is built.The reverse bias I-V characteristics and micro-plasma noise were measured in it, before and after Gamma irradiation. It is...A correlation model between micro plasma noise and gamma irradiation of GaN-based LED is built.The reverse bias I-V characteristics and micro-plasma noise were measured in it, before and after Gamma irradiation. It is found that even after 30 krad Gamma irradiation, the GaN-based LED has soft breakdown failure. The reverse soft breakdown region current local instability of this device before irradiation is analyzed by the microplasma noise method. The results were obtained that if the GaN-based LED contained micro-plasma defects, it will fail after low doses(30 krad) of gamma irradiation. The results clearly reflect the micro-plasma defects induced carriers fluctuation noise and the local instability of GaN-based LED reverse bias current.展开更多
The transmitting light in GaN-based LED with 30 nm thickness metal film grating is investigated. We proposed a basic grating structure model to enhance light intensity in GaN material, which was simpler and cheaper. W...The transmitting light in GaN-based LED with 30 nm thickness metal film grating is investigated. We proposed a basic grating structure model to enhance light intensity in GaN material, which was simpler and cheaper. We calculated and analyzed the structure with different parameters, and studied the numerical simulation results of Ag-films/Al-films/Au-films. With a simple A1 or Ag basic grating structure, the 7.4-7.6 times intensity of 550 nm light can be obtained easily, and the enhancement efficiency is better than others.展开更多
基金This research was funded by the National Key Research and Development Program of China(2022YFB2802803)the Natural Science Foundation of China Project(No.61925104,No.62031011,No.62201157,No.62074072).
文摘Although the 5G wireless network has made significant advances,it is not enough to accommodate the rapidly rising requirement for broader bandwidth in post-5G and 6G eras.As a result,emerging technologies in higher frequencies including visible light communication(VLC),are becoming a hot topic.In particular,LED-based VLC is foreseen as a key enabler for achieving data rates at the Tb/s level in indoor scenarios using multi-color LED arrays with wavelength division multiplexing(WDM)technology.This paper proposes an optimized multi-color LED array chip for high-speed VLC systems.Its long-wavelength GaN-based LED units are remarkably enhanced by V-pit structure in their efficiency,especially in the“yellow gap”region,and it achieves significant improvement in data rate compared with earlier research.This work investigates the V-pit structure and tries to provide insight by introducing a new equivalent circuit model,which provides an explanation of the simulation and experiment results.In the final test using a laboratory communication system,the data rates of eight channels from short to long wavelength are 3.91 Gb/s,3.77 Gb/s,3.67 Gb/s,4.40 Gb/s,3.78 Gb/s,3.18 Gb/s,4.31 Gb/s,and 4.35 Gb/s(31.38 Gb/s in total),with advanced digital signal processing(DSP)techniques including digital equalization technique and bit-power loading discrete multitone(DMT)modulation format.
文摘The optical properties of GaN-based blue light-emitting diodes(LEDs)are extremely important to study as these LEDs are utilized in a great many industries due to their excellent qualities,including high brightness,high energy efficiency,low energy consumption,and rapid reaction time.In this paper,Silvaco TCAD simulation software is used to do two-dimensional modeling and simulation of a GaN-based blue single quantum well vertical structure LED,with an emphasis on varied forward voltages,In components in InGaN,and quantum well thickness.The volt-ampere characteristic curve is compared and evaluated,as well as the energy band structure,carrier concentration,radiation recombination efficiency,electroluminescence spectrum,and internal current density distribution.The results show that when the forward voltage is 3.5V and the thickness of the quantum well is constant,the luminescence spectrum will show a red shift with the increase of the In content in the quantum well,and the luminescence spectrum will also show a red shift when the thickness of the quantum well is increased.However,when the quantum well thickness and In component are kept constant,the luminescence spectrum appears a red shift with increasing forward voltage.
基金Project supported by the National Natural Science Foundation for Young Scientists of China(Grant Nos.61704069 and 51602141)the National Key Research and Development Program of China(Grant No.2016YFB0400601)
文摘GaN-based yellow light-emitting diodes(LEDs) on Si substrates are aged at a direct current density of 50 A/cm^2 for500 h. After the aging process, it can be found that the LEDs have a stable electrical property but their light output power is decayed by 4.01% at 35 A/cm^2. Additionally, the aging mechanism of GaN-based yellow LED is analyzed. It is found that the decay of light output power may be attributed to the following two reasons: one is the increase of Shockley–Rrad–Hall recombination and the other is the change of the transport path of holes via V-pits after aging, which may induce the radiative recombination current to decrease. In this paper, not only the aging mechanism of GaN-based yellow LED is investigated, but also a new possible research direction in LED aging is given.
基金Project supported by the National Natural Science Foundation of China(Grant No.61334009)the National High Technology Research and Development Program of China(Grant Nos.2015AA03A101 and 2014BAK02B08)+1 种基金China International Science and Technology Cooperation Program(Grant No.2014DFG62280)the"Import Outstanding Technical Talent Plan"and"Youth Innovation Promotion Association Program"of the Chinese Academy of Sciences
文摘Progress with GaN-based light emitting diodes (LEDs) that incorporate nanostructures is reviewed, especially the re- cent achievements in our research group. Nano-patterned sapphire substrates have been used to grow an A1N template layer for deep-ultraviolet (DUV) LEDs. One efficient surface nano-texturing technology, hemisphere-cones-hybrid nanostruc- tures, was employed to enhance the extraction efficiency of InGaN flip-chip LEDs. Hexagonal nanopyramid GaN-based LEDs have been fabricated and show electrically driven color modification and phosphor-free white light emission because of the linearly increased quantum well width and indium incorporation from the shell to the core. Based on the nanostruc- tures, we have also fabricated surface plasmon-enhanced nanoporous GaN-based green LEDs using AAO membrane as a mask. Benefitting from the strong lateral SP coupling as well as good electrical protection by a passivation layer, the EL intensity of an SP-enhanced nanoporous LED was significantly enhanced by 380%. Furthermore, nanostructures have been used for the growth of GaN LEDs on amorphous substrates, the fabrication of stretchable LEDs, and for increasing the 3-dB modulation bandwidth for visible light communication.
基金supported by the National Natural Science Foundation of China (Grant No. 60777013)the Nature Science Foundation of Beijing,China (Grant No. 4082023)the Excellent Doctoral Science and Technology Innovation Foundation of Beijing Jiaotong University,China (Grant No. 141063522)
文摘GaN-based irregular multiple quantum well (IMQW) structures assembled two different types of QWs emitting complementary wavelengths for dichromatic white light-emitting diodes (LEDs) are optimized in order to obtain near white light emissions. The hole distributions and spontaneous emission spectra of the IMQW structures are analysed in detail by fully considering the effects of strain, well-coupling, valence band-mixing and polarization effect through employing a newly developed theoretical model from the k. p theory. Several structure parameters such as well material component, well width, layout of the wells and the thickness of harrier between different types of QWs are employed to analyse how these parameters together with the polarization effect influence the electronic and the optical properties of IMQW structure. Numerical results show that uniform hole distributions in different types of QWs are obtained when the number of the QWs emitting blue light is two, the number of the QWs emitting yellow light is one and the barrier between different types of QWs is 8nm in thickness. The near white light emission is realized using GaN-based IMQW structure with appropriate design parameters and injection level.
基金Supported by the National Key Research and Development Program under Grant No 2016YFB0400902the Science and Technology Project of State Grid Corporation of China under Grant No SGSDDKOOKJJS1600071
文摘Design, fabrication and characterizations of GaN-based blue micro light emitting diode (LED) arrays are reported. The GaN micro-LED array consists of 320×256 pixels with a pitch size of 30μm. Each pixel is 25×25μm^2 in size, which is designed for backside emission and high density flip-chip packaging. The selected LED pixels being tested exhibit good uniformity in terms of turn-on voltage and reverse leakage current. The efficiency droop behavior and reliability behavior under high forward current stress are also studied. The micro-LED pixel shows improved reliability, which is likely caused by enhanced heat dissipation.
基金Project supported by the National Natural Science Foundation of China(Grant No.60877069)the Science and Technology Key Program of Guangdong Province,China(Grant Nos.2011A081301004 and 2012A080304006)
文摘GaN-based multiple quantum well light-emitting diodes (LEDs) with conventional and superlattice barriers have been investigated numerically. Simulation results demonstrate using InGaN/GaN superlattices as barriers can effectively enhance performances of the GaN-Based LEDs, mainly owing to the improvement of hole injection and transport among the MQW active region. Meanwhile, the improved electron capture decreases the electron leakage and alleviates the efficiency droop. The weak polarization field induced by the superlattice structure strengthens the intensity of the emission spectrum and leads to a blue-shift relative to the conventional one.
文摘GaN/InGaN lighting-emitting diodes with different mesa structures are studied. The current-voltage characteristics, light output power, luminous efficiency, and peak wavelength of the GaN/InGaN lighting-emitting diodes with different mesa patterns are compared. It shows that the current-voltage characteristics of the chips with more mesa areas are im- proved greatly by reducing the current crowding. With higher injection current the light output powers of GaN-based LED with more mesa areas are enhanced. And the chips with more P-electrode area have a smaller red shift and a little bit blue shift due to the reduction of the current crowding.
基金Project supported by the Education Department Science and Technology Foundation of Jiangxi Province(No.GJJ160743)the Doctoral Research Start-Up Foundation of Jinggangshan University(No.JZB15001)
文摘A correlation model between micro plasma noise and gamma irradiation of GaN-based LED is built.The reverse bias I-V characteristics and micro-plasma noise were measured in it, before and after Gamma irradiation. It is found that even after 30 krad Gamma irradiation, the GaN-based LED has soft breakdown failure. The reverse soft breakdown region current local instability of this device before irradiation is analyzed by the microplasma noise method. The results were obtained that if the GaN-based LED contained micro-plasma defects, it will fail after low doses(30 krad) of gamma irradiation. The results clearly reflect the micro-plasma defects induced carriers fluctuation noise and the local instability of GaN-based LED reverse bias current.
基金supported by the National Natural Science Foundation of China(No.60976070)
文摘The transmitting light in GaN-based LED with 30 nm thickness metal film grating is investigated. We proposed a basic grating structure model to enhance light intensity in GaN material, which was simpler and cheaper. We calculated and analyzed the structure with different parameters, and studied the numerical simulation results of Ag-films/Al-films/Au-films. With a simple A1 or Ag basic grating structure, the 7.4-7.6 times intensity of 550 nm light can be obtained easily, and the enhancement efficiency is better than others.