共查询到20条相似文献,搜索用时 11 毫秒
1.
T. C. Wen S. J. Chang Y. K. Su L. W. Wu C. H. Kuo W. C. Lai J. K. Sheu T. Y. Tsai 《Journal of Electronic Materials》2003,32(5):419-422
High-quality InGaN/GaN multiple-quantum well (MQW) light-emitting diode (LED) structures were prepared by a temperature-ramping
method during metal-organic chemical-vapor deposition (MOCVD) growth. Two photoluminescence (PL) peaks, one originating from
well-sensitive emission and one originating from an InGaN quasi-wetting layer on the GaN-barrier surface, were observed at
room temperature (RT). The observation of high-order double-crystal x-ray diffraction (DCXRD) satellite peaks indicates that
the interfaces between InGaN-well layers and GaN-barrier layers were not degraded as we increased the growth temperature of
the GaN-barrier layers. With a 20-mA and 160-mA current injection, it was found that the output power could reach 2.2 mW and
8.9 mW, respectively. Furthermore, it was found that the reliability of the fabricated green LEDs prepared by temperature
ramping was also reasonably good. 相似文献
2.
Kyoung Soo Yook Soon Ok Jeon Jun Yeob Lee Kum Hee Lee Young Soo Kwon Seung Soo Yoon Ji Hwan Yoon 《Organic Electronics》2009,10(7):1378-1381
High efficiency pure white organic light-emitting diodes (WOLEDs) were developed using a highly efficient diphenylaminofluorene-based deep blue fluorescent material (DAF). A high quantum efficiency of 7.1% with color coordinates of (0.15, 0.18) were obtained from the DAF-doped blue device, which was then combined with phosphorescent red/green devices. A mixed interlayer was used to control the color coordinates and charge balance in the emitting layer of the WOLEDs. The pure white hybrid WOLEDs showed a high quantum efficiency of 12.3%. 相似文献
3.
随着氮(N)面GaN材料生长技术的发展,基于N面GaN衬底的高亮度发光二极管(LED)的研究具有重要的科学意义.研究了具有高发光功率的N面GaN基蓝光LED的新型结构设计,通过在N面LED的电子阻挡层和多量子阱有源层之间插入p型InGaN/GaN超晶格来提高有源层中的载流子注入效率.为了对比N面GaN基LED优异的器件性能,同时设计了具有相同结构的Ga面LED.通过对两种LED结构的电致发光特性、有源层中能带图、电场和载流子浓度分布进行比较可以发现,N面LED在输出功率和载流子注入效率上比Ga面LED有明显的提升,从而表明N面GaN基LED具有潜在的应用前景. 相似文献
4.
C. S. Kim H. K. Cho M. K. Yoo H. S. Cheong C. -H. Hong H. K. Cho 《Journal of Electronic Materials》2004,33(5):445-449
Correlation between material properties of bulk p-GaN layers grown on undoped GaN and device performance of InGaN/GaN blue
light-emitting diodes (LEDs) as a function of p-GaN growth temperature were investigated. The p-GaN layers of both structures
grown by metal-organic chemical-vapor deposition were heavily doped with Mg. As the growth temperature of the bulk p-GaN layer
increased up to 1,080°C, NA-ND increased. However, above 1,110°C, NA-ND sharply decreased, while the fluctuation of Mg concentration ([Mg]) increased. At this time, a peculiar surface, which originated
from inversion domain boundaries (IDBs), was clearly observed in the bulk p-GaN layer. The IDBs were not found in all LEDs
because the p-GaN contact layer was relatively thin. The change in photoluminescence emission from the ultraviolet band to
blue band is found to be associated with the fluctuation of [Mg] and IDBs in bulk p-GaN layers. The LED operating voltage
and reverse voltage improved gradually up to the p-GaN contact-layer growth temperature of 1,080°C. However, the high growth
temperature of 1,110°C, which could favor the formation of IDBs in the bulk p-GaN layer, yielded poorer reverse voltage and
saturated output power of the LEDs. 相似文献
5.
The typical light emission efficiency behaviors of InGaN/GaN multi-quantum well (MQW) blue light- emitting diodes (LEDs) grown on c-plane sapphire substrates are characterized by pulsed current operation mode in the temperature range 40 to 300 K. At temperatures lower than 80 K, the emission efficiency of the LEDs decreases approximately as an inverse square root relationship with drive current. We use an electron leakage model to explain such efficiency droop behavior; that is, the excess electron leakage into the p-side of the LEDs under high forward bias will significantly reduce the injection possibility of holes into the active layer, which in turn leads to a rapid reduction in the radiative recombination efficiency in the MQWs. Combining the electron leakage model and the quasi-neutrality principle in the p-type region, we can readily derive the inverse square root dependent function between the light emission efficiency and the drive current. It appears that the excess electron leakage into the p-type side of the LEDs is primarily responsible for the low-temperature efficiency droop behavior. 相似文献
6.
We present a comparative study on temperature dependence of electroluminescence (EL) of InGaN/GaN multiple-quantum-well (MQW)
light-emitting diodes (LEDs) with identical structure but different indium contents in the active region. For the ultraviolet
(UV) and blue LEDs, the EL intensity decreases dramatically with decreasing temperature after reaching a maximum at 150 K.
The peak energy exhibits a large redshift in the range of 20–50 meV with a decrease of temperature from 200 K to 70 K, accompanying
the appearance of longitudinal-optical (LO) phonon replicas broadening the low energy side of the EL spectra. This redshift
is explained by carrier relaxation into lower energy states, leading to dominant radiative recombination at localized states.
In contrast, the peak energy of the green LED exhibits a minimal temperature-induced shift, and the emission intensity increases
monotonically with decreasing temperature down to 5 K. We attribute the different temperature dependences of the EL to different
degrees of the localization effects in the MQW regions of the LEDs. 相似文献
7.
D. I. Florescu D. S. Lee S. M. Ting J. C. Ramer E. A. Armour 《Journal of Electronic Materials》2003,32(11):1330-1334
The edge-emitting electroluminescence (FL) state of polarization of blue and green InGaN/GaN light-emitting diodes (LEDs)
grown in EMCORE’s commercial reactors was studied and compared to theoretical evaluations. Blue (∼475 nm) LEDs exhibit strong
EL polarization, up to a 3:1 distinction ratio. Green (∼530 nm) LEDs exhibit smaller ratios of about 1.5:1. Theoretical evaluations
for similar InGaN/GaN superlattices predicted a 3:1 ratio between light polarized perpendicular (E⊥c) and light polarized
parallel (E‖c) to the c axis. For the blue LEDs, a quantum well-like behavior is suggested because the E⊥c mode dominates
the E‖c mode 3:1. In contrast, for the green LEDs, a mixed quantum well (QW)-quantum dot (QD) behavior is proposed, as the
ratio of E⊥c to E‖c modes drops to 1.5:1. The EL polarization fringes were also observed, and their occurrence may be attributed
to a symmetric waveguide-like behavior of the InGaN/GaN LED structure. A large 40%/50% drop in the surface root mean square
(RMS) from atomic force microscopy (AFM) scans on blue/green LEDs with and without EL fringes points out that better surfaces
were achieved for the samples exhibiting fringing. At the same time, a 25%/10% increase in the blue/green LED photoluminescence
(PL) intensity signal was found for samples displaying EL interference fringes, indicating superior material quality and improved
LED structures. 相似文献
8.
InGaN/GaN light-emitting diodes with a reflector at the backside of sapphire substrates 总被引:1,自引:0,他引:1
Y. P. Hsu S. J. Chang Y. K. Su C. S. Chang S. C. Shei Y. C. Lin C. H. Kuo L. W. Wu S. C. Chen 《Journal of Electronic Materials》2003,32(5):403-406
Nitride-based light-emitting diodes (LEDs) with a reflector at the backside of the sapphire substrates have been demonstrated.
It was found that an SiO2/TiO2 distributed-Bragg reflector (DBR) structure could reflect more downward-emitting photons than an Al-mirror layer. It was
also found that the 20-mA output power was 2.76 mW, 2.65 mW, and 2.45 mW for the DBR LED, Al-reflector LED, and conventional
LED, respectively. With the same 50-mA current injection, the integrated-electroluminescence (EL) intensity of a DBR LED and
an Al-reflector LED was 19% and 15% larger than that observed from a conventional LED. 相似文献
9.
Toshiki Makimoto Kazuhide Kumarkura Toshio Nishida Naoki Kobayashi 《Journal of Electronic Materials》2002,31(4):313-315
Valence-band discontinuities between InGaN and GaN were evaluated using the capacitance-voltage characteristics of p-InGaN/n-GaN
heterojunction diodes with high hole concentrations in p-InGaN. This capacitance-voltage method is effective to evaluate valence-band
discontinuities because the influence of the piezoelectric charges at the heterojunction is ignored due to high acceptor concentrations.
The built-in potential obtained from the capacitance-voltage measurements decreased with the In mole fraction of p-InGaN.
This result indicates that the valence-band discontinuity (ΔEV) increases with the In mole fraction (x) and is expressed as ΔEV (eV)=0.85x for x≤0.28. The ΔEV value obtained in this work is about 50% lower than that reported previously using the photoluminescence (PL) method. 相似文献
10.
A. Y. Polyakov N. B. Smirnov A. V. Govorkov Jihyun Kim F. Ren G. T. Thaler R. M. Frazier B. P. Gila C. R. Abernathy S. J. Pearton I. A. Buyanova G. Y. Rudko W. M. Chen C. -C. Pan G. -T. Chen J. -I. Chyi J. M. Zavada 《Journal of Electronic Materials》2004,33(3):241-247
Electrical and electroluminescent properties were studied for GaN/InGaN light-emitting diodes (LEDs) with the n-GaN layer
up and with the top portion of the n layer made of undoped GaMnN to allow polarization modulation by applying an external
magnetic field (so-called “spin-LEDs”). The contact annealing temperature was kept to 750°C, which is the thermal stability
limit for retaining room-temperature magnetic ordering in the GaMnN layer. Measurable electroluminescence (EL) was obtained
in these structures at threshold voltages of ∼15 V, with a lower EL signal compared to control LEDs without Mn. This is related
to the existence of two parasitic junctions between the metal and the lower contact p-type layer and between the GaMnN and
the n-GaN in the top contact layer. 相似文献
11.
阴极蒸镀和隔离层对有机发光二极管性能的影响 总被引:1,自引:1,他引:1
制备了简单结构的有机发光二极管(OLED)ITO/NPB/Alq3/Al/Ag。实验结果表明,快速蒸镀法制备的Ag阴极越厚,器件性能越差,而慢速蒸镀200nmAg阴极时器件性能也较差。在Alq3与Al阴极之间插入BCP/C60/LiF隔离层后,即使快速蒸镀法制备的Ag厚达280nm,器件的最大电流密度、最大亮度和最大电流效率仍分别高达248.6mA/cm2、5380.7cd/m2和3.52cd/A。隔离层不仅保护NPB和Alq3基本不被玻璃化,还很好地与Alq3和Al阴极匹配,大大提高了器件性能。 相似文献
12.
通过自建装置精确测试了发光二极管(LED)的低频(小于102Hz)电学特性。电学测量表明,所有LED在低频下都表现出明显的负电容(NC)现象,且频率越低NC现象越明显。调制发光测量表明,相对发光强度在低频下表现出明显饱和现象,并且随频率增加而减小。比较电学和光学的测量结果可以证实,辐射发光是产生NC现象的主要原因。通过对LED电学测量结果的详细分析得出了NC随电压和频率的变化关系式。 相似文献
13.
GaN-based blue light-emitting diodes (LEDs) on various patterned sapphire substrates (PSSs) are investigated in detail. Hemispherical and triangular pyramidal PSSs have been applied to improve the performance of LEDs compared with conventional LEDs grown on planar sapphire substrate. The structural, electrical, and optical properties of these LEDs are investigated. The leakage current is related to the crystalline quality of epitaxial GaN films, and it is improved by using the PSS technique. The light output power and emission efficiency of the LED grown on triangular pyramidal PSS with optimized fill factor show the best performance in all the samples, which indicates that the pattern structure and fill factor of the PSS are related to the capability of light extraction. 相似文献
14.
基于红绿/蓝双发光层,制作了结构为ITO/MoO 3(10nm)/NPB(40nm)/TCTA(10nm)/CBP:R-4B(2%):GIR1(14%,X nm)/mCP:Firpic(8%,Y nm/BCP(10nm)/Alq3(40nm)/LiF(1nm)/Al( 100nm)的白色全磷光有机电致发光器件(OLED),通过 调节红绿发光层的厚度X与蓝光发光层的厚度Y,研究了不同发光层厚度器件发 光性能的影响。研究发现:当X 为23nm、Y为7nm时,器件的光效和色坐标都具有 很高的稳定性,在电压分别为5、 10和15V时,色坐标分别为(0.33,0.37)、(0.33,0. 37)和(0.34,0.38);在电压为 5V时,电流密度为0.674mA,亮度为158.7cd ,最大电流效率为26.87cd/A;利用电子阻 挡材料TCTA和空穴阻挡材料BCP能够显著提高载流子的复合效率。分析认为:发光层顺序 为红绿/蓝时,更有利于蓝光的出射,从而使白光的色坐标更稳定。 相似文献
15.
X. A. Cao S. F. LeBoeuf K. H. Kim P. M. Sandvik E. B. Stokes A. Ebong D. Walker J. Kretchmer J. Y. Lin H. X. Jiang 《Solid-state electronics》2002,46(12):2291-2294
The mechanisms of carrier injection and recombination in a GaN/InGaN single quantum well light-emitting diodes have been studied. Strong defect-assisted tunneling behavior has been observed in both forward and reverse current–voltage characteristics. In addition to band-edge emission at 400 nm, the electroluminescence has also been attributed to radiative tunneling from band-to-deep level states and band-to-band tail states. The approximately current-squared dependence of light intensity at 400 nm even at high currents indicates dominant nonradiative recombination through deep-lying states within the space-charge region. Inhomogeneous avalanche breakdown luminescence, which is primarily caused by deep-level recombination, suggests a nonuniform spatial distribution of reverse leakage in these diodes. 相似文献
16.
17.
Jungeun Park Hankook Oh Sihyun Oh Jinho Kim Hyun Jin Park Oh Young Kim Jun Yeob Lee Youngjin Kang 《Organic Electronics》2013,14(12):3228-3233
Highly efficient deep blue phosphorescent organic light-emitting diodes (PHOLEDs) using two heteroleptic iridium compounds, (dfpypy)2Ir(acac) and (dfpypy)2Ir(dpm), as a dopant and 9-(3-(9H-carbazol-9-yl)phenyl)-9H-carbazol-3-yl)diphenylphosphine oxide as a host material have been developed. The electroluminescent device of (dfpypy)2Ir(dpm) at the doping level of 3 wt% shows the best performance with external quantum efficiency of 18.5–20.4% at the brightness of 100–1000 cd/m2 and the color coordinate of (0.14, 0.18) at 1000 cd/m2. 相似文献
18.
《Organic Electronics》2014,15(5):1071-1075
An Al complex, tris((2-(pyrazol-1-yl)pyridin-3-yl)oxy)aluminum (Al(pypy)3), was synthesized as a high triplet energy host material for blue phosphorescent organic light-emitting diodes. A high triplet energy ligand, 2-(1H-pyrazol-1-yl)pyridin-3-ol, was coordinated to the Al to develop the high triplet energy host material derived from Al. The Al(pypy)3 host showed a high triplet energy of 2.86 eV for efficient energy transfer to blue triplet emitter. A maximum quantum efficiency of 20.5% was achieved in blue device using the Al(pypy)3 host material. 相似文献
19.
20.
In this paper,size effects on optical performance of blue light-emitting diodes(LEDs)are investigated.The essential physical mechanism is studied by fabricating LEDs with various sizes of the active area and testing optical characteristics.It is found that micro-LEDs have better light extracting efficiency and thermal dissipation compared with broad-area LEDs,which is likely due to the small ratio of perimeter and active area.Furthermore,micro-LEDs are more beneficial for displays due to the stable wavelength under the low pulse width modulation(PWM)current density. 相似文献