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.     

Effect of Different Quantum Well Structures on the Output Power Performance of GaN-Based Light-Emitting Diodes

We investigated the effect of two different quantum well (QW) structures having different indium contents on the optical performance of fully packaged GaN-based light-emitting diodes (LEDs). Dual-spectrum QW LEDs exhibit ～4% higher external quantum efficiency (at 350 mA) than single-spectrum QW LEDs. However, the two types of LEDs exhibit similar efficiency droop behavior. For both types of LEDs, the output power decreases with increasing junction temperature. When the junction temperature exceeds 70°C, the dual-spectrum QW LEDs exhibit lower output power than the single-spectrum QW LEDs. The wavelength dependence of the output power (at 350 mA) of single-spectrum QW LEDs shows that the LEDs with shorter wavelengths experience more rapid optical degradation than the LEDs with longer wavelengths. Based on the wavelength- and junction-temperature-dependent output power, the droop behavior of the dual-spectrum QW LEDs is described and discussed.     

MOCVD生长双有源区AlGaInP发光二极管

设计并用金属有机物化学气相沉积方法生长了双有源区AlGaInP发光二极管,该发光二极管的两个AlGaInP有源区用高掺杂的反偏隧道结连接.双有源区发光二极管在20 mA注入电流下,主波长为623 nm,峰值波长为633 nm,电压为4.16 V,光强为163 mcd.     

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。     

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。     

复合布拉格反射镜高亮度AlGaInP发光二极管

采用光学薄膜理论中干涉矩阵模型计算了峰值波长为630nm的AlGaInP红光LED的Al0.6Ga0.4As/AlAs材料的常规DBR和复合DBR的反射谱特性,用LP-MOCVD方法生长了模拟设计的DBR结构,测量了其白光反射谱,实验与模拟结果基本符合.制备了采用Al0.6Ga0.4As/AlAs复合DBR的LED器件,未封装输出光功率为2.3mW,外量子效率为5.6%,发光效率可达12 lm/W,比常规DBR器件提高了35%.验证了复合DBR与常规DBR相比,可以大幅度提高AlGaInP红光LED的出光效率.     

Study of the emission extraction efficiency of mesa-LEDs with a narrow-gap InAsSb active region

A series of light-emitting diodes (LEDs) (emission peak wavelength λ_max = 3.6 μm) with cone-shaped mesas, which have concave lateral surfaces and heights between 10 to 130 μm, has been developed. The dependence of the emission efficiency for these LEDs on mesa height has been studied at different injection currents at the temperatures 77 and 298 K. The form of the dependence observed is in agreement with the results of theoretical calculations. It is shown that the effective absorption coefficient, caused by emission extraction from the crystal, may be as large as 3 cm⁻¹ for LEDs with the highest mesa (130 μm) among the diodes in this series. The emission extraction coefficient is close to 30% at the temperature 298 K and 94% at 77 K.     

(Al)GaInP multiquantum well LEDs on GaAs and Ge

MOVPE growth of AlGaInP layers on GaAs and Ge have been demonstrated. The surface morphology of the epilayers was smooth under optimized growth conditions. The epilayers showed good PL intensity on both GaAs and Ge substrates. It has been observed that at room temperature the PL intensity drops in the first few seconds after excitation and attains a steady state. The Zn-doped AlGaInP did not show any signs of H-passivation. The MQW LEDs on both the substrates produced electroluminescence which increased with applied current. Results indicate the feasibility of AlGaInP LEDs on Ge.     

Dynamic Thermal Analysis of High-Power LEDs at Pulse Conditions

In this letter, the thermal evaluation of high-power LED packages at pulse conditions was reported. A theoretical calculation model was proposed based on the analogy between the thermal and electrical RC circuits. The thermal performance of LED packages driven by pulse input was calculated using the RC network extracted from transient thermal measurement. The junction temperature fluctuation band decreases with the frequency at certain duty cycles. The saturated average junction temperature rise linearly increases with the duty cycle at certain frequencies. These predictions were verified by the real-time junction temperature measurement using the peak shift method at pulse conditions. The theoretical model was found to be effective and applicable to the evaluation of the thermal performance of LEDs working at pulse conditions.     

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.     

Thermal measurements and analysis of AlGaInP/GaInP MQW red LEDs with different chip sizes and substrate thicknesses

Thermal properties of AlGaInP/GaInP MQW red LEDs are investigated by thermal measurements and analysis for different chip sizes and substrate thicknesses. To extract the thermal resistance (R_th), junction temperature (T_j) is experimentally determined by both forward voltage and electroluminescence (EL) emission peak shift methods. For theoretical thermal analysis, thermal parameters are calculated in simulation using measured heat source densities. The T_j value increases with increasing the injection current, and it decreases as the chip size becomes larger. The use of a thin substrate improves the heat removal capability. At 450 mA, the T_j values of 315 K and 342 K are measured for 500 × 500 μm² LEDs with 110 μm and 350 μm thick substrates, respectively. For 500 × 500 μm² LEDs with 110 μm thick substrate, the R_th values of 13.99 K/W and 14.89 K/W are obtained experimentally by the forward voltage and EL emission peak shift methods, respectively. The theoretically calculated value is 13.44 K/W, indicating a good agreement with the experimental results.     

Characteristics of high power LEDs at high and low temperature

The high power light emitting diodes(LEDs) based on InGaN and AlGaInP individually are tested on line at temperatures from -30 to 100℃.The data are fitted to measure the relationship between temperature and the properties of forward voltage,relative light intensity,wavelength,and spectral bandwidth of two different kinds of LEDs.Why these properties changed and how these changes reflected on applications are also analyzed and compared with each other.The results show that temperature has a great influence on the performance and application of power LEDs.For applications at low temperature,the forward voltage rising and the peak wavelength blue-shifting must be considered;and at high temperature,the relative light intensity decreasing and the peak wavelength red-shifting must be considered.     

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.     

高可靠高亮度AlGaInP发光二极管

分析了隧道再生双有源区A lG aInP发光二极管的工作原理,测试了不同注入电流下管芯的轴向光强,得到了轴向光强随注入电流的变化关系。20 mA注入电流条件下,发射峰值波长为620 nm的隧道再生双有源区A lG aInP发光二极管,透明封装成视角15°后平均轴向光强达到5.5 cd。对透明封装成15°隧道再生双有源区发光二极管进行了寿命实验,在温度为25°C、30 mA直流电流条件下,隧道再生双有源区A lG aInP发光二极管的寿命超过了1.2×105h。     

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。     

具有纳米级结构出光面的AlGaInP基发光二极管

研究了一种利用金属自组装纳米掩膜和ICP刻蚀对AlGaInP基发光二极管(LED)表面进行粗化的技术,使光输出得到了提高.粗化了的AlGaInP基LED比常规的AlGaInP基LED,光强提高了27%,光功率提高了12.6%,实验结果具有可重复性.可以进一步优化Au颗粒的周期和分散程度,提高AlGaInP基LED的提取效率.     

Improvement of AlGaInP light emitting diode by sulfide passivation

The brightness of AlGaInP light emitting diodes (LEDs) has been raised by a factor of 1.12 at 20 mA by sulfide passivation. Meanwhile, the sulfide also can decrease leakage current of AlGaInP LEDs at -2 V to nearly one thousandth of that in the as-fabricated device. The possible causes for the brightness increase of AlGaInP LEDs after sulfide treatment including surface roughness, reduction of Fresnel loss, and effective injection of carriers were demonstrated.     

透明导电ITO欧姆接触的AlGaInP薄膜发光二极管

提出了一种透明导电氧化铟锡(ITO)欧姆接触的AlGaInP薄膜发光二极管(LED)的结构和制作工艺.在这个结构里,ITO还作为窗口层材料,增强电流扩展,并应用了高反射率的金属作为反光镜.用Au-Sn合金(Au∶Sn＝8∶2,重量比)作为焊料,把带有金属反光镜的AlGaInP LED(RS-LED)外延片倒装键合到GaAs基板上,并去掉外延GaAs衬底,把被GaAs衬底吸收的光反射出去.与常规AlGaInP吸收衬底LEDs(AS-LED)和带有分布布拉格反光镜(DBR)的AlGaInP吸收衬底LEDs(DBR-AS-LED)电、光特性的比较,用透明导电ITO做欧姆接触的AlGaInP薄膜RS-LED结构能极大提高光输出功率和发光强度.正向电流20 mA时,RS-LED的光输出功率分别是AS-LED和DBR-AS-LED的2.4倍和1.7倍;RS-LED 20 mA下峰值波长624 nm的轴向光强达到了179.6 mcd,分别是AS-LED 20 mA下峰值波长627 nm和DBR-AS-LED 20 mA下峰值波长623 nm轴向光强的2.2倍和1.3倍.     

AlGaInP系LED的表面纳米级粗化以及光提取效率提高

分析了常规AlGaInP系发光二极管（LED）光提取效率低的主要原因,半导体的折射率与空气折射率相差很大,导致全反射使有源区产生的光子绝大部分不能通过出光面发射到体外。通过在LED出光层采用纳米压印技术引入表面纳米结构,以改变光子的传播路径,从而使得更多的光子能够发射到体外。理论分析与实验结果表明,与常规平面结构相比,...     

Phosphor Thermometry in White Light-Emitting Diodes

A method for the in situ measurement of phosphor temperature in high-power white light-emitting diodes (LEDs) was demonstrated. The method is based on the dependence of the fluorescence decay time in inorganic phosphors on temperature. The decay time was estimated using the frequency-domain technique, which relies on the measurement of the phase shift of the sinusoidal waveform of fluorescence relative to that of the photoexcitation, obtained by driving the LED at high-frequency current. LEDs containing a single phosphor ("cool-white") and a phosphor blend ("warm-white") were examined. By comparison of the phosphor temperature with that of the LED junction and metal mount, the character of the spatial profile of temperature within the LED packages was revealed