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 impact of the V-pits covering layer(VCL) position on the optoelectronic performance of InGaN-based green light-emitting diodes(LEDs) was investigated. It is found that earlier covering of V-pits will hinder the ho...The impact of the V-pits covering layer(VCL) position on the optoelectronic performance of InGaN-based green light-emitting diodes(LEDs) was investigated. It is found that earlier covering of V-pits will hinder the hole injection via the sidewall of V-pits, and then result in less quantum wells(QWs) participating in radioluminescence. The current-voltage characteristics show that the LEDs with earlier covering of V-pits have higher operating voltage at room temperature, and a more dramatic voltage rise with the reduction of temperature. Meanwhile, more manifested emission peaks for sidewall QWs and deeper QWs near to ntype layer was observed in the sample with earlier coveing of V-pits at cryogenic temperatures, for the reason that the holes being injected via V-pits sidewall have higher kinetic energy and could transport to deeper QWs.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
Although the solid-state lighting market is growing rapidly, it is still difficult to obtain ultra-high brightness white light emitting diodes(LEDs). V-pits are inevitably introduced during the metalorganic chemical v...Although the solid-state lighting market is growing rapidly, it is still difficult to obtain ultra-high brightness white light emitting diodes(LEDs). V-pits are inevitably introduced during the metalorganic chemical vapor deposition(MOCVD)growth of multiple quantum wells(MQWs) in Ⅲ–nitride LEDs, and thus affecting the carrier dynamics of the LEDs.Specifically designed structures are fabricated to study the influence of the V-pits on the hole transportation and efficiency droop, and double quantum wells(QWs) are used to monitor the transportation and distribution of holes based on their emission intensity. It is found that when compared with the planar QWs, the injection of holes into the QWs through the side walls of the V-pits changes the distribution of holes among the MQWs. This results in a higher probability of hole injection into the middle QWs and enhanced emission therein, and, consequently, a lower efficiency droop.展开更多
This paper reports that a dual-wavelength white light-emitting diode is fabricated by using a metal-organic chemical vapor deposition method. Through a 200-hours＇ current stress, the reverse leakage current of this l...This paper reports that a dual-wavelength white light-emitting diode is fabricated by using a metal-organic chemical vapor deposition method. Through a 200-hours＇ current stress, the reverse leakage current of this light-emitting diode increases with the aging time, but the optical properties remained unchanged despite the enhanced reverse leakage current. Transmission electron microscopy and cathodeluminescence images show that indium atoms were assembled in and around V-shape pits with various compositions, which can be ascribed to the emitted white light. Evolution of cathodeluminescence intensities under electron irradiation is also performed. Combining cathodeluminescence intensities under electron irradiation and above results, the increase of leakage channels and crystalline quality degradation are realized. Although leakage channels increase with aging, potential fluctuation caused by indium aggregation can effectively avoid the impact of leakage channels. Indium aggregation can be attributed to the mechanism of preventing optical degradation in phosphor-free white light-emitting diode.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.
基金supported by the State Key Program of the National Science Foundation of China(Grant No.61334001)the National Key R&D Program of China(Grant Nos.2016YFB0400600 and 2016YFB0400601)Development Program of Jiangxi province(Grant No.20165ABC28007 and No20182ABC28003)
文摘The impact of the V-pits covering layer(VCL) position on the optoelectronic performance of InGaN-based green light-emitting diodes(LEDs) was investigated. It is found that earlier covering of V-pits will hinder the hole injection via the sidewall of V-pits, and then result in less quantum wells(QWs) participating in radioluminescence. The current-voltage characteristics show that the LEDs with earlier covering of V-pits have higher operating voltage at room temperature, and a more dramatic voltage rise with the reduction of temperature. Meanwhile, more manifested emission peaks for sidewall QWs and deeper QWs near to ntype layer was observed in the sample with earlier coveing of V-pits at cryogenic temperatures, for the reason that the holes being injected via V-pits sidewall have higher kinetic energy and could transport to deeper QWs.
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 Key Research and Development Project of China(Grant No.2017YFB0403303)the Key Technologies Research and Development Program of Tianjin,China(Grant Nos.18YFZCGX00760 and 18YFZCGX00400)
文摘Although the solid-state lighting market is growing rapidly, it is still difficult to obtain ultra-high brightness white light emitting diodes(LEDs). V-pits are inevitably introduced during the metalorganic chemical vapor deposition(MOCVD)growth of multiple quantum wells(MQWs) in Ⅲ–nitride LEDs, and thus affecting the carrier dynamics of the LEDs.Specifically designed structures are fabricated to study the influence of the V-pits on the hole transportation and efficiency droop, and double quantum wells(QWs) are used to monitor the transportation and distribution of holes based on their emission intensity. It is found that when compared with the planar QWs, the injection of holes into the QWs through the side walls of the V-pits changes the distribution of holes among the MQWs. This results in a higher probability of hole injection into the middle QWs and enhanced emission therein, and, consequently, a lower efficiency droop.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60990314, 60976009, 60577146, U0834001)the National Key Basic Research and Development Project (973) of China (Grant No. 2007CB307004)
文摘This paper reports that a dual-wavelength white light-emitting diode is fabricated by using a metal-organic chemical vapor deposition method. Through a 200-hours＇ current stress, the reverse leakage current of this light-emitting diode increases with the aging time, but the optical properties remained unchanged despite the enhanced reverse leakage current. Transmission electron microscopy and cathodeluminescence images show that indium atoms were assembled in and around V-shape pits with various compositions, which can be ascribed to the emitted white light. Evolution of cathodeluminescence intensities under electron irradiation is also performed. Combining cathodeluminescence intensities under electron irradiation and above results, the increase of leakage channels and crystalline quality degradation are realized. Although leakage channels increase with aging, potential fluctuation caused by indium aggregation can effectively avoid the impact of leakage channels. Indium aggregation can be attributed to the mechanism of preventing optical degradation in phosphor-free white light-emitting diode.
