InGaN/GaN MQWs structures were grown by MOCVD. The effects of the growth interruption time on the optical and structural properties of InGaN/GaN MQWs were investigated. The experimental results show that the growth in...InGaN/GaN MQWs structures were grown by MOCVD. The effects of the growth interruption time on the optical and structural properties of InGaN/GaN MQWs were investigated. The experimental results show that the growth interruption can improve the interface quality, increase the intensity of photoluminescence (PL) and electroluminescence (EL); but if the interruption time was too long, the well thickness and the average In composition of MQWs decreased, and the EL intensity also decreased due to poor interface quality and impurities derived from growth interruption.展开更多
Photoluminescence(PL)characteristics of the structure consisting of green InGaN/GaN multiple quantum wells(MQWs)and low indium content InGaN/GaN pre-wells are investigated.Several PL peaks from pre-wells and green InG...Photoluminescence(PL)characteristics of the structure consisting of green InGaN/GaN multiple quantum wells(MQWs)and low indium content InGaN/GaN pre-wells are investigated.Several PL peaks from pre-wells and green InGaN/GaN MQWs are observed.The peak energy values for both pre-wells and green InGaN/GaN MQWs display an S-shaped variation with temperature.In addition,the differences in the carrier localization effect,defect density,and phonon-exciton interaction between the pre-wells and green InGaN/GaN MQWs,and the internal quantum efficiency of the sample are studied.The obtained results elucidate the mechanism of the luminescence characteristics of the sample and demonstrate the significant stress blocking effect of pre-wells.展开更多
The InGaN films and GaN/InGaN/GaN tunnel junctions(TJs)were grown on GaN templates with plasma-assisted molecular beam epitaxy.As the In content increases,the quality of InGaN films grown on GaN templates decreases an...The InGaN films and GaN/InGaN/GaN tunnel junctions(TJs)were grown on GaN templates with plasma-assisted molecular beam epitaxy.As the In content increases,the quality of InGaN films grown on GaN templates decreases and the surface roughness of the samples increases.V-pits and trench defects were not found in the AFM images.p++-GaN/InGaN/n++-GaN TJs were investigated for various In content,InGaN thicknesses and doping concentration in the InGaN insert layer.The InGaN insert layer can promote good interband tunneling in GaN/InGaN/GaN TJ and significantly reduce operating voltage when doping is sufficiently high.The current density increases with increasing In content for the 3 nm InGaN insert layer,which is achieved by reducing the depletion zone width and the height of the potential barrier.At a forward current density of 500 A/cm^(2),the measured voltage was 4.31 V and the differential resistance was measured to be 3.75×10^(−3)Ω·cm^(2)for the device with a 3 nm p++-In_(0.35)Ga_(0.65)N insert layer.When the thickness of the In_(0.35)Ga_(0.65)N layer is closer to the“balanced”thickness,the TJ current density is higher.If the thickness is too high or too low,the width of the depletion zone will increase and the current density will decrease.The undoped InGaN layer has a better performance than n-type doping in the TJ.Polarization-engineered tunnel junctions can enhance the functionality and performance of electronic and optoelectronic devices.展开更多
The nano-patterned InGaN film was used in green InGaN/GaN multiple quantum wells(MQWs)structure,to relieve the unpleasantly existing mismatch between high indium content InGaN and GaN,as well as to enhance the light o...The nano-patterned InGaN film was used in green InGaN/GaN multiple quantum wells(MQWs)structure,to relieve the unpleasantly existing mismatch between high indium content InGaN and GaN,as well as to enhance the light output.The different self-assembled nano-masks were formed on InGaN by annealing thin Ni layers of different thicknesses.Whereafter,the InGaN films were etched into nano-patterned films.Compared with the green MQWs structure grown on untreated InGaN film,which on nano-patterned InGaN had better luminous performance.Among them the MQWs performed best when 3 nm thick Ni film was used as mask,because that optimally balanced the effects of nano-patterned InGaN on the crystal quality and the light output.展开更多
Miniaturization of light-emitting diodes(LEDs) with sizes down to a few micrometers has become a hot topic in both academia and industry due to their attractive applications on self-emissive displays for high-definiti...Miniaturization of light-emitting diodes(LEDs) with sizes down to a few micrometers has become a hot topic in both academia and industry due to their attractive applications on self-emissive displays for high-definition televisions,augmented/mixed realities and head-up displays, and also on optogenetics, high-speed light communication, etc. The conventional top-down technology uses dry etching to define the LED size, leading to damage to the LED side walls.Since sizes of microLEDs approach the carrier diffusion length, the damaged side walls play an important role, reducing microLED performance significantly from that of large area LEDs. In this paper, we review our efforts on realization of microLEDs by direct bottom-up growth, based on selective area metal–organic vapor phase epitaxy. The individual LEDs based on either GaN nanowires or InGaN platelets are smaller than 1 μm in our approach. Such nano-LEDs can be used as building blocks in arrays to assemble microLEDs with different sizes, avoiding the side wall damage by dry etching encountered for the top-down approach. The technology of InGaN platelets is especially interesting since InGaN quantum wells emitting red, green and blue light can be grown on such platelets with a low-level of strain by changing the indium content in the InGaN platelets. This technology is therefore very attractive for highly efficient microLEDs of three primary colors for displays.展开更多
Room temperature low threshold lasing of green GaNbased vertical cavity surface emitting laser(VCSEL)was demonstrated under continuous wave(CW)operation.By using self-formed InGaN quantum dots(QDs)as the active region...Room temperature low threshold lasing of green GaNbased vertical cavity surface emitting laser(VCSEL)was demonstrated under continuous wave(CW)operation.By using self-formed InGaN quantum dots(QDs)as the active region,the VCSEL emitting at 524.0 nm has a threshold current density of 51.97 A cm^(-2),the lowest ever reported.The QD epitaxial wafer featured with a high IQE of 69.94%and theδ-function-like density of states plays an important role in achieving low threshold current.Besides,a short cavity of the device(~4.0λ)is vital to enhance the spontaneous emission coupling factor to 0.094,increase the gain coefficient factor,and decrease the optical loss.To improve heat dissipation,AlN layer was used as the current confinement layer and electroplated copper plate was used to replace metal bonding.The results provide important guidance to achieving high performance GaN-based VCSELs.展开更多
In order to clarify the origin of the efficiency droop effect in InGaN based blue multiple-quantum-well(MQW)light emitting diodes(LEDs),a reasonable model is set up,taking all the possible factor(carrier delocalizatio...In order to clarify the origin of the efficiency droop effect in InGaN based blue multiple-quantum-well(MQW)light emitting diodes(LEDs),a reasonable model is set up,taking all the possible factor(carrier delocalization,carrier leakage and Auger recombination)into account.By fitting the external quantum efficiency-injection current(η–Ⅰ)measurements of two LED samples,the validity of the model is demonstrated.The fit results show that the main origin of efficiency droop at a high injection current is carrier leakage.Furthermore it is also indicated that carrier delocalization plays an important role in the efficiency droop effect in those LEDs of large localization degree.展开更多
Carrier transport via the V-shaped pits （V-pits） in InGaN/GaN multiple-quantum-well （MQW） solar cells is numer- ically investigated. By simulations, it is found that the V-pits can act as effective escape paths fo...Carrier transport via the V-shaped pits （V-pits） in InGaN/GaN multiple-quantum-well （MQW） solar cells is numer- ically investigated. By simulations, it is found that the V-pits can act as effective escape paths for the photo-generated carriers. Due to the thin barrier thickness and low indium composition of the MQW on V-pit sidewall, the carriers entered the sidewall QWs can easily escape and contribute to the photocurrent. This forms a parallel escape route for the carries generated in the fiat quantum wells. As the barrier thickness of the fiat MQW increases, more carriers would transport via the V-pits. Furthermore, it is found that the V-pits may reduce the recombination losses of carriers due to their screening effect to the dislocations. These discoveries are not only helpful for understanding the carrier transport mechanism in the InGaN/GaN MQW, but also important in design of the structure of solar cells.展开更多
基金National Natural Science Foundation ofChina (grant No. 60506012) and Beijing Education committeeFound( No. KZ200510005003)
文摘InGaN/GaN MQWs structures were grown by MOCVD. The effects of the growth interruption time on the optical and structural properties of InGaN/GaN MQWs were investigated. The experimental results show that the growth interruption can improve the interface quality, increase the intensity of photoluminescence (PL) and electroluminescence (EL); but if the interruption time was too long, the well thickness and the average In composition of MQWs decreased, and the EL intensity also decreased due to poor interface quality and impurities derived from growth interruption.
基金Project supported by the Science Challenge Project,China(Grant No.TZ2016003)National Key Research and Development Program of China(Grant Nos.2016YFB0400803 and 2017YFE0131500)the Fund from the State Key Laboratory of Optoelectronic Materials and Technologies,Sun Yat-sen University,China。
文摘Photoluminescence(PL)characteristics of the structure consisting of green InGaN/GaN multiple quantum wells(MQWs)and low indium content InGaN/GaN pre-wells are investigated.Several PL peaks from pre-wells and green InGaN/GaN MQWs are observed.The peak energy values for both pre-wells and green InGaN/GaN MQWs display an S-shaped variation with temperature.In addition,the differences in the carrier localization effect,defect density,and phonon-exciton interaction between the pre-wells and green InGaN/GaN MQWs,and the internal quantum efficiency of the sample are studied.The obtained results elucidate the mechanism of the luminescence characteristics of the sample and demonstrate the significant stress blocking effect of pre-wells.
基金supported by the National Key Research and Development Program of China (2017YFE0131500, 2022YFB2802801)the National Natural Science Foundation of China (61834008, U21A20493)+1 种基金the Key Research and Development Program of Jiangsu Province (BE2020004, BE2021008-1)the Suzhou Key Laboratory of New-type Laser Display Technology (SZS2022007)
文摘The InGaN films and GaN/InGaN/GaN tunnel junctions(TJs)were grown on GaN templates with plasma-assisted molecular beam epitaxy.As the In content increases,the quality of InGaN films grown on GaN templates decreases and the surface roughness of the samples increases.V-pits and trench defects were not found in the AFM images.p++-GaN/InGaN/n++-GaN TJs were investigated for various In content,InGaN thicknesses and doping concentration in the InGaN insert layer.The InGaN insert layer can promote good interband tunneling in GaN/InGaN/GaN TJ and significantly reduce operating voltage when doping is sufficiently high.The current density increases with increasing In content for the 3 nm InGaN insert layer,which is achieved by reducing the depletion zone width and the height of the potential barrier.At a forward current density of 500 A/cm^(2),the measured voltage was 4.31 V and the differential resistance was measured to be 3.75×10^(−3)Ω·cm^(2)for the device with a 3 nm p++-In_(0.35)Ga_(0.65)N insert layer.When the thickness of the In_(0.35)Ga_(0.65)N layer is closer to the“balanced”thickness,the TJ current density is higher.If the thickness is too high or too low,the width of the depletion zone will increase and the current density will decrease.The undoped InGaN layer has a better performance than n-type doping in the TJ.Polarization-engineered tunnel junctions can enhance the functionality and performance of electronic and optoelectronic devices.
基金the National Natural Science Foundation of China(Grant No.62074120)the State Key Laboratory on Integrated Optoelectronics(Grant No.IOSKL2018KF10)the Fundamental Research Funds for the Central Universities(Grant No.JB211108).
文摘The nano-patterned InGaN film was used in green InGaN/GaN multiple quantum wells(MQWs)structure,to relieve the unpleasantly existing mismatch between high indium content InGaN and GaN,as well as to enhance the light output.The different self-assembled nano-masks were formed on InGaN by annealing thin Ni layers of different thicknesses.Whereafter,the InGaN films were etched into nano-patterned films.Compared with the green MQWs structure grown on untreated InGaN film,which on nano-patterned InGaN had better luminous performance.Among them the MQWs performed best when 3 nm thick Ni film was used as mask,because that optimally balanced the effects of nano-patterned InGaN on the crystal quality and the light output.
基金supported by the Swedish Research Council (VR),the Foundation for Strategic Research (SSF),the Knut and Alice Wallenberg foundation (KAW),the Swedish Energy Agency and Sweden’s innovation agency (VINNOVA)。
文摘Miniaturization of light-emitting diodes(LEDs) with sizes down to a few micrometers has become a hot topic in both academia and industry due to their attractive applications on self-emissive displays for high-definition televisions,augmented/mixed realities and head-up displays, and also on optogenetics, high-speed light communication, etc. The conventional top-down technology uses dry etching to define the LED size, leading to damage to the LED side walls.Since sizes of microLEDs approach the carrier diffusion length, the damaged side walls play an important role, reducing microLED performance significantly from that of large area LEDs. In this paper, we review our efforts on realization of microLEDs by direct bottom-up growth, based on selective area metal–organic vapor phase epitaxy. The individual LEDs based on either GaN nanowires or InGaN platelets are smaller than 1 μm in our approach. Such nano-LEDs can be used as building blocks in arrays to assemble microLEDs with different sizes, avoiding the side wall damage by dry etching encountered for the top-down approach. The technology of InGaN platelets is especially interesting since InGaN quantum wells emitting red, green and blue light can be grown on such platelets with a low-level of strain by changing the indium content in the InGaN platelets. This technology is therefore very attractive for highly efficient microLEDs of three primary colors for displays.
基金This work was supported by the National Natural Science Foundation of China(Nos.U21A20493,62104204,and 62234011)the National Key Research and Development Program of China(No.2017YFE0131500)the President’s Foundation of Xiamen University(No.20720220108).
文摘Room temperature low threshold lasing of green GaNbased vertical cavity surface emitting laser(VCSEL)was demonstrated under continuous wave(CW)operation.By using self-formed InGaN quantum dots(QDs)as the active region,the VCSEL emitting at 524.0 nm has a threshold current density of 51.97 A cm^(-2),the lowest ever reported.The QD epitaxial wafer featured with a high IQE of 69.94%and theδ-function-like density of states plays an important role in achieving low threshold current.Besides,a short cavity of the device(~4.0λ)is vital to enhance the spontaneous emission coupling factor to 0.094,increase the gain coefficient factor,and decrease the optical loss.To improve heat dissipation,AlN layer was used as the current confinement layer and electroplated copper plate was used to replace metal bonding.The results provide important guidance to achieving high performance GaN-based VCSELs.
基金by the National Basic Research Program of China under Grant Nos 2011CB301902 and 2011CB301903the National High-Technology Research and Development Program of China under Grant Nos 2011AA03A112,2011AA03A106,and 2011AA03A105+2 种基金the National Key Technology Research and Development Program of the Ministry of Science and Technology of China(No 2011BAE01B07)the National Natural Science Foundation of China under Grant Nos 60723002,50706022,60977022 and 51002085the Beijing Natural Science Foundation under Grant No 4091001.
文摘In order to clarify the origin of the efficiency droop effect in InGaN based blue multiple-quantum-well(MQW)light emitting diodes(LEDs),a reasonable model is set up,taking all the possible factor(carrier delocalization,carrier leakage and Auger recombination)into account.By fitting the external quantum efficiency-injection current(η–Ⅰ)measurements of two LED samples,the validity of the model is demonstrated.The fit results show that the main origin of efficiency droop at a high injection current is carrier leakage.Furthermore it is also indicated that carrier delocalization plays an important role in the efficiency droop effect in those LEDs of large localization degree.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61564007 and 11364034)the Sci-Tech Support Plan of Jiangxi Province,China(Grant No.20141BBE50035)
文摘Carrier transport via the V-shaped pits （V-pits） in InGaN/GaN multiple-quantum-well （MQW） solar cells is numer- ically investigated. By simulations, it is found that the V-pits can act as effective escape paths for the photo-generated carriers. Due to the thin barrier thickness and low indium composition of the MQW on V-pit sidewall, the carriers entered the sidewall QWs can easily escape and contribute to the photocurrent. This forms a parallel escape route for the carries generated in the fiat quantum wells. As the barrier thickness of the fiat MQW increases, more carriers would transport via the V-pits. Furthermore, it is found that the V-pits may reduce the recombination losses of carriers due to their screening effect to the dislocations. These discoveries are not only helpful for understanding the carrier transport mechanism in the InGaN/GaN MQW, but also important in design of the structure of solar cells.
