GaN基功率LED高低温特性研究

首次对自制的GaN基大功率白光和蓝光发光二极管在-30~100°C的温度下进行了在线的光电特性测试,对两种不同LED的正向电压、相对光强、波长、色温等参数随温度变化的关系进行了数据曲线拟合,对比分析了参数变化的原因,以及这些变化对实际应用的影响。结果表明,温度对大功率LED的光电特性有很大影响,通过对比发现白光LED的部分光参数随温度的变化不仅与GaN芯片有关,同时受到荧光粉的影响。低温环境下,要考虑LED的正向电压升高和峰值波长蓝移对应用的影响;而高温条件下要考虑光功率降低和峰值波长红移对应用的影响。     

Degradation of AlGaN-based ultraviolet light emitting diodes

Aging the LEDs by driving at high current, results in the decrease of optical power proportional to the reciprocal square route of stress time. With aging time, change in the current–voltage characteristics indicates decrease of the current at low voltage below the light emission threshold, decrease of the forward voltage drop at high currents and usually no change in the series resistance. No change in the peak wavelength and half bandwidth were found with aging. Low frequency noise measured at low and high currents either did not depend on aging time or decreased. No correlation between noise, the device power, and the rate of the power degradation were found. These results are in strong contrast to previous studies of longer wavelength GaN-based LEDs. The possible degradation mechanism is the diffusion of the Al atoms out from the p-type cladding layer and lowering of the cladding layer potential barrier as a result.     

p-AlGaN/GaN超晶格做p型层350 nm紫外AlGaN基LED

使用p-AlGaN/p-GaN SPSLs作为LED的p型层,在蓝宝石衬底上生长出发光波长为350 nm的AlGaN基紫外LED。[JP+1]由于AlGaN/GaN超晶格的极化效应,使得Mg受主的电离能降低,大幅提高了器件的光学和电学性能。在工作电流为350 mA下发光亮度达到了22.66 mW,相应的工作电压为3.75 V,LEDs的光功率满足了实际应用需求。     

一体化封装LED结温测量与发光特性研究

基于一体化封装基板,制备了大功率白光LED。以低热阻的一体化封装基板为基础,设计了结温测量系统。利用光谱仪测得不同结温下LED的光电参数,并对其机理进行了分析。在工作电流为0.34A,所研究温度范围为10.8～114.9℃。实验结果表明,一体化封装的LED结温与正向电压、光通量、光效和色温有着良好的线性关系;结温的变化对主波长及色坐标影响甚微;结温的上升导致蓝光段强度下降且光谱发生红移,黄光段强度上升且光谱发生宽化,峰值波长由450nm转为550nm。     

Nitride-based green light-emitting diodes with high temperature GaN barrier layers

High-quality InGaN-GaN multiquantum well (MQW) light-emitting diode (LED) structures were prepared by temperature ramping method during metalorganic chemical vapor deposition (MOCVD) growth. It was found that we could reduce the 20-mA forward voltage and increase the output intensity of the nitride-based green LEDs by increasing the growth temperature of GaN barrier layers from 700/spl deg/C to 950/spl deg/C. The 20-mA output power and maximum output power of the nitride-based green LEDs with high temperature GaN barrier layers was found to be 2.2 and 8.9 mW, respectively, which were more than 65% larger than those observed from conventional InGaN-GaN green LEDs. Such an observation could be attributed to the improved crystal quality of GaN barrier layers. The reliability of these LEDs was also found to be reasonably good.     

MOCVD生长双波长发光二极管

根据白光照明和可变换波长的光通信中对单芯片双波长发光二极管(LED)要求,在分析了反向偏置隧道结性质的基础上,设计了用反向偏置隧道结连接两个有源区的单芯片双波长LED,用金属有机化学气相沉积技术(MOCVD)在GaAs衬底上一次外延生长了同时发射两种波长的LED,其包含一个AlGaInP量子阱有源区和一个GaInP量子阱有源区,两个有源区由隧道结连接;通过后工艺制备了双波长LED器件,在20mA电流注入下,可以同时发射626nm和639nm两种波长,光强是127mcd,正向电压是4.17V。与传统的单有源区LED进行对比表明,双波长LED有较强的光强;对比单有源区LED的2.08V正向电压,考虑到双波长LED包含隧道结和两个有源区,隧道结上的压降很小。     

Maintenance of stable light emission in high power LEDs

As well known, the light emission characteristics of the high power light-emitting diodes (LEDs) are very sensitive to the various driving conditions, especially the injected electric current and the junction temperature in operation. In this work, the dependency of the emission light from high power LEDs upon the driving electric current and the junction temperature will be explored in details. One integrated measurement system is proposed for the study in simultaneously obtaining all the thermal–optic–electric characteristics of LEDs throughout the measuring. Based on the basic feedback control methodology, one simple maintaining procedure is applied for the stable light emission in high power LEDs. It shows the robustness of the maintaining procedure from the environment change with the least heat dissipation in the operation of the high power LEDs. The results imply that all the thermal, the optic, and the electric properties of the high power LEDs should be taken into consideration in the same time rather than separately when maintaining their operation.     

Improvement in light-output efficiency of AlGaInP LEDs fabricated on stripe patterned epitaxy

Quaternary AlGaInP light-emitting diodes (LEDs) operating at a wavelength of 630 nm with a stripe-patterned omni-directional reflector (ODR) were fabricated. It is demonstrated that the geometrical shape of stripe-patterned structure improves the light extraction efficiency by increasing the extraction of guided light. The optical and electrical characteristics of stripe-patterned ODR LEDs are presented and compared to typical ODR and distributed Bragg reflector (DBR) LEDs with the same epitaxial structure and emitting wavelength. It is shown that the output power of the stripe-patterned ODR LED exceeds that of the typical ODR and DBR LEDs by a factor of 1.15 and 2 times, respectively, and with an acceptable forward voltage of about 2.2 V.     

Highly Reliable High-Brightness GaN-Based Flip Chip LEDs

The properties of indium-tin-oxide (ITO)/Ni films as transparent ohmic contacts of nitride-based flip chip (FC) light emitting diodes (LEDs) were studied. It was found that 300degC rapid thermal annealed (RTA) ITO(15 nm)/Ni(1 nm) could provide good electrical and optical properties for FC LED applications. It was also found that 20-mA operation voltage and output power of the 465-nm FC LEDs with ITO/Ni/Ag reflective mirror were 3.16 V and 21 mW, respectively. Furthermore, it was found that output intensity of the proposed LED only decayed by 5% after 1200 h under 30-mA current injection at room temperature.     

Early degradation of high power packaged LEDs under humid conditions and its recovery — Myth of reliability rejuvenation

A sharp rise in lumen degradation was observed for packaged high power LEDs during the initial period of operation under high humidity and temperature conditions, and the degradation reaches a peak value, followed by a “recovery” in lumen output, a sign of reliability rejuvenation. The time to reach the peak degradation is shorter with higher relative humidity. Scanning acoustic microscopy (SAM) tomography is employed to study the effect of moisture at different time intervals. With the help of moisture diffusion modeling using ANSYS simulation, the phenomenon is found to be due to the increasing moisture absorption of silicone resulting in subsequent light scattering as light is emitting from the dice. The “recovery” is the result of moisture absorption by die attach material that sucks the moisture from the silicone. Thus the “recovery” of lumen degradation is actually associated with the degradation in the internal structure of the LED package which is not reversible. C-SAM results are in accordance with the simulation and experimental results. The implication of this finding on temperature–humidity test of high power LEDs is described, and the material parameters of silicone to reduce this initial degradation are also presented.     

An integrated PIN/MISS OEIC for high current photoreceiverapplications

A new PIN/MISS photoreceiver with very high output current has been developed by using the combination of an amorphous silicon germanium alloy PIN photodiode and a metal-insulator-semiconductor switch (MISS) device. The developed photoreceiver uses a PIN photodiode as the light absorption structure and light wavelength selector and the MISS device as an actuator to drive an electronic load. Based on the experimental results, the photoreceiver yields a very high output current of 3.2 mA at a voltage bias of 6 V under an incident light power of P_in=100 μW, and has a rise time of 465 μs with a load resistance of R=1 kΩ. The peak response wavelength of the PIN photodiode is at 905 nm, i.e., infrared light. Thus the high output current PIN/MISS photoreceiver is a good candidate for some specific applications     

固定相关色温下三基色合成白光LED的光谱优化

通常获得白光LED的高光视效能（K）往往是以降低其显色指数（Ra）为代价的,本文在固定相关色温（CCT）为3 000±10 K下,通过调配三基色白光LED光谱参数来寻求K和Ra的最佳平衡。模拟结果表明：当三基色白光LED的3个峰值波长分别为467、550和618 nm,半高宽（FWHM）分别为30、71和23 nm以及...     

功率型LED电压温度系数的研究

理论上详细分析了LED正向电压随温度变化的物理机理,并在大的电流范围(0.1～200 mA)和温度范围(60～350 K)内,对AlGaInP、InGaN材料系功率型LED正向电压随温度的变化关系进行了系统的实验研究.发现在恒定电流下,两者的变化关系可分为高温区和低温区两段.在高温区两者为线性反比关系,并且电压温度系数与正向电流有关,在低温区正向电压随温度减小而突然急剧增大.理论很好地解释了实验结果.     

有机／聚合物双异质结发光二极管

报道了用有机／聚合物薄膜材料制备的双异质结发光二极管。器件结构为：玻璃衬底／ＩＴＯ／ＰＶＫ／ＡｌｑＰＢＤ／Ａｌｑ３／Ａｌ电极。在这种结构器件中，电子和空穴分别从Ａｌ负电极和ＩＴＯ正电极中注入，产在ＰＢＤ及ＰＶＫ中传输注入到Ａｌｑ３发光层中。器件在正向偏压为４Ｖ时有绿色光输出；在正向偏压为１０Ｖ，最大亮度可达３０００ｃｄ／ｍ＾２以上。经光谱测试，电致发光峰值波长为５２３ｎｍ。     

p-GaN与ITO欧姆接触的研究

针对GaN基发光二极管中p-GaN与透明导电薄膜ITO之间的接触进行研究,尝试找出透明导电层ITO的优化制程条件。将在不同氧流量、ITO厚度及退火温度下制备的透明电极ITO薄膜应用于GaN基发光二极管,来增加电流扩展,减小ITO与p-GaN欧姆接触电阻,降低LED工作电压及提高透过率、增强LED发光亮度。将ITO薄膜应用于218μm×363μm GaN基发光二极管LED,分析其在20 mA工作电流条件下正向电压和光输出功率的变化,在优化条件下制得的蓝光LED在直流电流20 mA下的正向电压3.23 V,光输出效率为23.25 mW。     

GaN基白光LED温度特性实验研究

实验研究了恒流驱动条件下,GaN基白光LED的正向电压、发光光谱和发光效率随环境温度的变化情况.结果表明,在输入电流恒定的情况下,随着温度的升高,结电压和发光强度与温度具有良好的线性关系,并且GaN基白光LED的发光颜色总是向蓝光漂移,而小电流驱动时比大电流驱动时蓝光漂移更明显.根据实验结果,分析了器件的最佳额定工作电流.

Abstract：

Under a constant driving current, the changes of the forward voltage, emission spectrum and luminous efficiency of GaN-based White LEDs with the ambient temperature are studied experimentally. It is found that the forward voltage and the luminous intensity depend on the temperature linearly with constant injection current, and luminous colors of GaN-based White LEDs always shift towards blue. And the blue shift with low driving current is more obvious than that with high driving current. According to the results, the best rated operating current of GaN-based white LEDs is discussed.     

Characteristics of a-Plane Green Light-Emitting Diode Grown on r-Plane Sapphire

In this work, we have successfully grown a-plane green light-emitting diodes (LEDs) on r-plane sapphire and investigated the device characteristics of a-plane green LEDs. The apparent emission polarization anisotropy was observed and the polarization degree was as high as 67.4%. In addition, the electroluminescence (EL) spectra first revealed a wavelength blue-shift with increasing drive current to 20 mA, which could be attributed to the band-filling effect, and then the EL peak become constant. The current–voltage curve showed the forward voltage of a-plane LED grown on r-plane sapphire substrate was 3.43 V and the differential series resistance was measured to be about 24 $Omega $ as 20-mA injected current. Furthermore, the output power was 240 $mu hbox{W}$ at 100-mA drive current.      

Degradation behaviors of GaN light-emitting diodes under high-temperature and high-current stressing

A number of commercially available multiple-quantum well (MQW) InGaN/GaN blue LEDs with wavelengths of about 460 nm and a power of 1 mW were stressed at temperatures ranging from 25 to 120 °C at several accelerated DC currents. Both the forward and reverse current voltage characteristics as well as the electroluminescent spectra of the LEDs were monitored. These effects also resulted in the pronounced degradation of light efficiency and device operation lifetime. We found that the degradation of photonic characteristics, correlated very well with the generation-recombination current which is governed by the defect density. The device degradation is much faster at high temperatures. At nominal operation current and at room temperature, the light intensity degradation reaches a saturation level before the light dyes out. These results shed new lights upon the design and lifetime specifications for the emerging commercial solid-state lighting devices.     

SiO_2:Er和Si_xO_2:Er薄膜室温Er~(3+)1.54μm波长的电致发光

在 n+ -Si衬底上用磁控溅射淀积掺 Er氧化硅 (Si O2 :Er)薄膜和掺 Er富硅氧化硅 (Six O2 :Er,x>1 )薄膜 ,薄膜经适当温度退火后 ,蒸上电极 ,形成发光二极管 (LED)。室温下在大于 4V反偏电压下发射了来自 Er3+的 1 .5 4μm波长的红外光。测量了由 Si O2 :Er/n+ -Si样品和 Six O2 :Er/n+ -Si样品分别制成的两种 LED,其 Er3+1 .5 4μm波长的电致发光峰强度 ,后者明显比前者强。还发现电致发光强度与 Si O2 :Er/n+ -Si样品和 Six O2 :Er/n+ -Si样品的退火温度有一定依赖关系     

Water bonding of 50-mm-diameter mirror substrates to AlGaInP light-emitting diode wafers

The feasibility of bonding 50-mm-diameter Si with a Au/AuBe mirror to AlGaInP light-emitting diode (LED) wafers is demonstrated. Wafer bonding over the entire wafer area is achieved while the metallic mirror still maintains high reflectivity. Using this technique, the mirror-substrate AlGaInP LEDs are fabricated across an entire 50-mm wafer. The test data show that 98% of the dice with operating voltages <2.2 V at 20 mA and 85% of the dice with luminous intensity in the 130∼140 mcd region. The wafer-bonded mirror-substrate LED lamps operating at 626 nm can emit 3 lm at 20 mA with a forward voltage of 2 V, corresponding to a luminous efficiency of 74 lm/W. Moreover, they present a peak power efficiency of 21% with 4 mW output at 10 mA (1.9 V). Essentially no degradation is observed for these LEDs after 2000 h stress at 80°C and 50 mA (55.6 A/cm²). The results indicate the mirror-substrate AlGaInP LEDs of highly reliable and efficient performance.