Inhomogeneous electroluminescence(EL)of InGaN green LEDs grown on mesh-patterned Si(111)substrate had been investigated.Sample with n-AlGaN inserted between the pre-strained layers and the first quantum well showed th...Inhomogeneous electroluminescence(EL)of InGaN green LEDs grown on mesh-patterned Si(111)substrate had been investigated.Sample with n-AlGaN inserted between the pre-strained layers and the first quantum well showed the inhomogeneous EL in the low current density range.Near-field EL emission intensity distribution images depicted that inhomogeneity in the form of premature turn-on at the periphery of the LED chip,results in stronger emission intensity at the edges.This premature turn-on effect significantly reduces the luminous efficacy and higher ideality factor value due to locally current crowding effect.Raman measurement and fluorescence microscopy results indicated that the partially relaxed in-plane stress at the edge of the window region acts as a parasitic diode with a smaller energy band gap,which is a source of edge emission.Numerical simulations showd that the tilted triangular n-AlGaN functions like a forward-biased Schottky diode,which not only impedes carrier transport,but also contributes a certain ideality factor.展开更多
InGaN-based green light-emitting diodes （LEDs） with different growth temperatures of superlattice grown on Si （111） substrates are investigated by temperature-dependent electroluminescence between 100 K and 350K. ...InGaN-based green light-emitting diodes （LEDs） with different growth temperatures of superlattice grown on Si （111） substrates are investigated by temperature-dependent electroluminescence between 100 K and 350K. It is observed that with the decrease of the growth temperature of the superlattice from 895℃ to 855℃, the forward voltage decreases, especially at low temperature. We presume that this is due to the existence of the larger average size of V-shaped pits, which is determined by secondary ion mass spectrometer measurements. Meanwhile, the sample with higher growth temperature of superlattice shows a severer efficiency droop at cryogenic temperatures （about 100 K-150 K）. Electron overflow into p-GaN is considered to be the cause of such phenomena, which is relevant to the poorer hole injection into multiple quantum wells and the more reduced effective active volume in the active region.展开更多
In GaN-based green light-emitting diodes（LEDs） with and without Mg-preflow before the growth of p-Al GaN electron blocking layer（EBL） are investigated experimentally.A higher Mg doping concentration is achieved in...In GaN-based green light-emitting diodes（LEDs） with and without Mg-preflow before the growth of p-Al GaN electron blocking layer（EBL） are investigated experimentally.A higher Mg doping concentration is achieved in the EBL after Mg-preflow treatment,effectively alleviating the commonly observed efficiency collapse and electrons overflowing at cryogenic temperatures.However,unexpected decline in quantum efficiency is observed after Mg-preflow treatment at room temperature.Our conclusions are drawn such that the efficiency decline is probably the result of different emission positions.Higher Mg doping concentration in the EBL after Mg-preflow treatment will make it easier for a hole to be injected into multiple quantum wells with emission closer to pGaN side through the（8-plane rather than the V-shape pits,which is not favorable to luminous efficiency due to the preferred occurrence of accumulated strain relaxation and structural defects in upper QWs closer to p-GaN.Within this framework,apparently disparate experimental observations regarding electroluminescence properties,in this work,are well reconciled.展开更多
GaN-based blue light emitting diodes （LEDs） have undergone great development in recent years, but the improvement of green LEDs is still in progress. Currently, the external quantum efficiency （EQE） of GaN-based g...GaN-based blue light emitting diodes （LEDs） have undergone great development in recent years, but the improvement of green LEDs is still in progress. Currently, the external quantum efficiency （EQE） of GaN-based green LEDs is typically 30%, which is much lower than that of top-level blue LEDs. The current challenge with regard to GaN-based green LEDs is to grow a high quality InGaN quantu.m well （QW） with low strain. Many techniques of improving efficiency are discussed, such as inserting A1GaN between the QW and the barrier, employing prestrained layers beneath the QW and growing semipolar QW. The recent progress of GaN-based green LEDs on Si substrate is also reported： high efficiency, high power green LEDs on Si substrate with 45.2% IQE at 35 A/cm2, and the relevant techniques are detailed.展开更多
基金the National Key Research and Development Program of China(Grant Nos.2017YFB0403105 and 2017YFB0403100)the National Natural Science Foundation of China(Grant Nos.11674147,61604066,51602141,and 11604137).
文摘Inhomogeneous electroluminescence(EL)of InGaN green LEDs grown on mesh-patterned Si(111)substrate had been investigated.Sample with n-AlGaN inserted between the pre-strained layers and the first quantum well showed the inhomogeneous EL in the low current density range.Near-field EL emission intensity distribution images depicted that inhomogeneity in the form of premature turn-on at the periphery of the LED chip,results in stronger emission intensity at the edges.This premature turn-on effect significantly reduces the luminous efficacy and higher ideality factor value due to locally current crowding effect.Raman measurement and fluorescence microscopy results indicated that the partially relaxed in-plane stress at the edge of the window region acts as a parasitic diode with a smaller energy band gap,which is a source of edge emission.Numerical simulations showd that the tilted triangular n-AlGaN functions like a forward-biased Schottky diode,which not only impedes carrier transport,but also contributes a certain ideality factor.
基金Supported by the National Natural Science Foundation of China under Grant No 61334001the National Key Research and Development Program of China under Grant Nos 2016YFB0400600,2016YFB0400601 and 2016YFB0400100+1 种基金the National Science Foundation for Young Scientists of China under Grant No 21405076the Fund for Less Developed Regions of the National Natural Science Foundation of China under Grant No 11364034
文摘InGaN-based green light-emitting diodes （LEDs） with different growth temperatures of superlattice grown on Si （111） substrates are investigated by temperature-dependent electroluminescence between 100 K and 350K. It is observed that with the decrease of the growth temperature of the superlattice from 895℃ to 855℃, the forward voltage decreases, especially at low temperature. We presume that this is due to the existence of the larger average size of V-shaped pits, which is determined by secondary ion mass spectrometer measurements. Meanwhile, the sample with higher growth temperature of superlattice shows a severer efficiency droop at cryogenic temperatures （about 100 K-150 K）. Electron overflow into p-GaN is considered to be the cause of such phenomena, which is relevant to the poorer hole injection into multiple quantum wells and the more reduced effective active volume in the active region.
基金Supported by the National Key R&D Program of China under Grant Nos 2016YFB0400600 and 2016YFB0400601the State Key Program of the National Natural Science of China under Grant No 61334001+2 种基金the Key R&D Program of Jiangxi Province under Grant No 20165ABC28007the Natural Science Foundation of Jiangxi Province under Grant No 20151BAB207053the National Natural Science Foundation of China under Grant No 21405076
文摘In GaN-based green light-emitting diodes（LEDs） with and without Mg-preflow before the growth of p-Al GaN electron blocking layer（EBL） are investigated experimentally.A higher Mg doping concentration is achieved in the EBL after Mg-preflow treatment,effectively alleviating the commonly observed efficiency collapse and electrons overflowing at cryogenic temperatures.However,unexpected decline in quantum efficiency is observed after Mg-preflow treatment at room temperature.Our conclusions are drawn such that the efficiency decline is probably the result of different emission positions.Higher Mg doping concentration in the EBL after Mg-preflow treatment will make it easier for a hole to be injected into multiple quantum wells with emission closer to pGaN side through the（8-plane rather than the V-shape pits,which is not favorable to luminous efficiency due to the preferred occurrence of accumulated strain relaxation and structural defects in upper QWs closer to p-GaN.Within this framework,apparently disparate experimental observations regarding electroluminescence properties,in this work,are well reconciled.
基金Project supported by the Key Program of the National Natural Science Foundation of China(Grant No.61334001)the National Natural Science Foundation of China(Grant Nos.11364034 and 21405076)+1 种基金the National Key Technology Research and Development Program of the Ministry of Science and Technology of China(Grant No.2011BAE32B01)the National High Technology Research and Development Program of China(Grant No.2011AA03A101)
文摘GaN-based blue light emitting diodes （LEDs） have undergone great development in recent years, but the improvement of green LEDs is still in progress. Currently, the external quantum efficiency （EQE） of GaN-based green LEDs is typically 30%, which is much lower than that of top-level blue LEDs. The current challenge with regard to GaN-based green LEDs is to grow a high quality InGaN quantu.m well （QW） with low strain. Many techniques of improving efficiency are discussed, such as inserting A1GaN between the QW and the barrier, employing prestrained layers beneath the QW and growing semipolar QW. The recent progress of GaN-based green LEDs on Si substrate is also reported： high efficiency, high power green LEDs on Si substrate with 45.2% IQE at 35 A/cm2, and the relevant techniques are detailed.
