晶圆键合和激光剥离工艺对GaN基垂直结构发光二极管芯片残余应力的影响

GaN基发光二极管(LED)中的残余应力状态对器件的性能和稳定性有很大影响. 通过使用三种不同的键合衬底(Al₂O₃衬底, CuW衬底和Si衬底)以及改变键合温度(290 ℃, 320 ℃, 350 ℃和380 ℃), 并且使用不同的激光能量密度(875, 945和1015 mJ·cm^-2) 进行激光剥离, 制备了不同应力状态的GaN基LED器件. 对不同条件下GaN LED进行弯曲度、Raman 散射谱测试. 实验结果表明, 垂直结构LED中的残余应力的状态是键合衬底和键合金属共同作用的结果, 而键合温度影响着垂直结构LED中的残余应力的大小. 激光剥离过程中, 一定能量密度下激光剥离工艺一般不会对芯片中的残余应力造成影响, 但是如果该工艺对GaN 层造成了微裂缝, 则会在一定程度上起到释放残余应力的作用. 使用Si衬底键合后, 外延蓝宝石衬底翘曲变大, 对应制备的GaN基垂直结构 LED中的残余应力为张应力, 并且随着键合温度的上升而变大; 而Al₂O₃和CuW衬底制备的LED中的残余应力为压应力, 但使用Al₂O₃衬底键合制备的LED中压应力随键合温度上升而一定程度变大, CuW 衬底制备的LED中压应力随键合温度上升而下降.     

GaN基高压发光二极管理想因子与单元个数关系研究

理想因子能够反映电流、载流子泄漏以及缺陷导致的非辐射复合等现象. 针对目前报道的GaN基发光二极管的理想因子的问题, 通过对高压发光二极管I-V曲线的拟合计算出了理想因子n的数值, 分别讨论了12 V, 19 V, 51 V 和80 V GaN基高压发光二极管的理想因子与其结构中串联晶粒个数的关系, 分析了理想因子大小与光谱半高宽(FWHM)的变化关系. 另外, 还对电流拥挤效应对理想因子的影响进行了分析. 结果表明: 高压发光二极管理想因子n随串联晶粒个数的增加几乎为线性规律增加, 高压发光二极管理想因子n是由其串联单元理想因子之和构成的. 这对GaN基高压发光二极管理想因子的研究具有参考价值.     

白光LED智能调光数学模型

LED灯的光通量不仅受电流的影响,还受到结温变化的影响。针对传统LED调光存在只改变电流大小而忽略结温变化对光通量影响所存在的不足,结合LED结温和管脚温度存在特定的关系,利用实验装置采集HL001WY型Ga N基白光LED在不同管脚温度和正向电流下的光通量实验数据并进行二次项趋势回归,利用定标和归一化方法建立光通量、电流以及管脚温度三者变化关系的数学模型。计算结果表明,利用该方法建立的模型得到的计算数值与实验实际测量值的相对误差小于4.5%。     

Comprehension of the effects of gamma ray on luminescence intensity of GaN-based light-emitting diodes with multi-quantum well

Wavelength dependent luminescence intensity is crucial relationship in determining the physical property of light-emitting diodes (LED). The first object of this work is to search for the applicable method of using wavelength to predict the normalization luminescence intensity, I/I _0max, launched from GaN-based LED with multi-quantum well before and after irradiation with ??-ray. Predicated on the principle of nonlinear curve fitting, a typical numerical method is highlighted because the wavelength-dependent luminescence intensity of the LED irradiated by ?? with different dose are quantitative analyzed by this method. The simulations agree very well with the observed spectroscopy of 5 curves for intensity versus wavelength. The minimum value of correlation coefficients between actual and calculated data is 0.993, and the maximum average relative error is 7.93%. Another object of this work is to find the relationship between radiation dose and key parameter of function described above in mathematics method. In the light of the calculated results, the influence of ?? on key parameter is explained successfully. The terminal benefit is that the normalization luminescence intensity, I/I _0max launched from GaN-based LED as a function of both wavelength and radiation dose is given in this paper.     

Enhanced carrier injection in InGaN/GaN multiple quantum wells LED with polarization-induced electron blocking barrier

In this report, we designed a light emitting diode (LED) structure in which an N-polar p-GaN layer is grown on top of Ga-polar In_0.1Ga_0.9N/GaN quantum wells (QWs) on an n-GaN layer. Numerical simulation reveals that the large polarization field at the polarity inversion interface induces a potential barrier in the conduction band, which can block electron overflow out of the QWs. Compared with a conventional LED structure with an Al_0.2Ga_0.8N electron blocking layer (EBL), the proposed LED structure shows much lower electron current leakage, higher hole injection, and a significant improvement in the internal quantum efficiency (IQE). These results suggest that the polarization induced barrier (PIB) is more effective than the AlGaN EBL in suppressing electron overflow and improving hole transport in GaN-based LEDs.     

GaN基白光LED的结温测量

用正向电压法、管脚法和蓝白比法等三种方法测量GaN基白光LED的结温,获得了较为准确的结温,误差可以控制在4℃以内.正向电压法在恒定电流的条件下,得到了正向电压与结温的线性关系;蓝白比法在不同环境温度和不同注入电流两种情况下,都得到了蓝白比与结温较好的线性关系.提出了蓝白比法可能的物理机制,提高环境温度和增大注入电流都会使结温升高,蓝光峰值波长也会改变,这两个因素都会影响荧光粉的激发和发光效率.降低结温需要考虑的主要因素有白光LED的接触电阻、串联电阻和外量子效率,封装材料的热导率,反射杯和管脚的设计,以及空气散热部分的散热面积等.     

牺牲Ni退火对硅衬底GaN基发光二极管p型接触影响的研究

本文通过在硅衬底发光二极管(LED)薄膜p-GaN表面蒸发不同厚度的Ni覆盖层,将其在N₂ ∶O₂=4 ∶1的气氛中、400℃—750℃的温度范围内进行退火,在去掉薄膜表面Ni覆盖层之后制备Pt/p-GaN欧姆接触层.实验结果表明:退火温度和Ni覆盖层厚度均对硅衬底GaN基LED薄膜p型欧姆接触有重要影响,Ni覆盖退火能够显著降低p型层中Mg受主的激活温度.经牺牲Ni退火后,p型比接触电阻率随退火温度的升高呈先变小后变大的规律,随Ni覆盖层厚度的增加呈先变小后变 关键词： 氮化镓 发光二极管 牺牲Ni退火 p型接触     

Impact of an indium oxide/indium-tin oxide mixed structure for GaN-based light-emitting diodes

An interesting GaN-based light emitting diode (LED) using a 50 nm indium oxide (In₂O₃)/250 nm indium-tin oxide (ITO) mixed structure to replace the commonly used ITO (250 nm) current spreading layer is fabricated and studied. Use of the In₂O₃ layer could reduce the contact resistance of p-GaN in LEDs. In addition, this highly-resistive In₂O₃ layer, below the ITO layer could improve the current spreading performance. Experimentally, at room temperature, using this mixed structure, the luminous and EL intensities are enhanced by 17.7 and 17.1%, respectively.     

Negative characteristic temperature of GaN-based blue laser diode investigated by numerical simulation

GaN-based blue laser diodes (LDs) may exhibit anomalous temperature characteristics such as a very high or negative characteristic temperature (T ₀). In this work, the temperature characteristics of blue LDs having InGaN double quantum-well (QW) active region are investigated using numerical simulation. It is found that the T ₀ is greatly influenced by the n-type doped barrier between the QWs and a negative T ₀ can be observed for the LD structure with a heavily doped barrier. The negative T ₀ of InGaN blue LDs is mainly attributed to the decrease of the Auger recombination rate at the p-side QW with increasing temperature as a result of the thermally enhanced hole transport from the p-side to the n-side QW.     

硅衬底氮化镓基LED薄膜转移至柔性黏结层基板后其应力及发光性能变化的研究

本文将硅(Si)衬底上外延生长的氮化镓(GaN)基发光二极管(LED)薄膜转移至含有柔性黏结层的基板上, 获得了不受衬底和支撑基板束缚的LED薄膜. 利用高分辨率X射线衍射仪(HRXRD)研究了薄膜转移前后的应力变化, 同时对其光致发光(PL)光谱的特性进行了研究. 结果表明: 硅衬底GaN基LED薄膜转移至柔性基板后, GaN受到的应力会由转移前巨大的张应力变为转移后微小的压应力, InGaN/GaN量子阱受到的压应力则增大; 尽管LED薄膜室温无损转移至柔性基板其InGaN阱层的In组分不会改变, 然而按照HRXRD倒易空间图谱通用计算方法会得出平均铟组发生了变化; GaN基LED薄膜从外延片转移至柔性基板时其PL谱会发生明显红移.     

GaN-based light-emitting diode with ZnO nanotexture layer prepared using hydrogen gas

ZnO films were deposited on indium tin oxide (ITO), which formed the transparent conductive layer (TCL) of a GaN-based light-emitting diode (LED), by ultrasonic spraying pyrolysis to increase the light output power. The ZnO nanotexture was formed by treating the as-deposited ZnO films with hydrogen. The root mean square (RMS) roughness increased from 4.47 to 7.89 nm before hydrogen treatment to 10.82-15.81 nm after hydrogen treatment for 20 min. Typical current-voltage (I-V) characteristics of the GaN-based LEDs with a ZnO nanotexture layer have a forward-bias voltage of 3.25 V at an injection current of 20 mA. The light output power of a GaN-based LED with a ZnO nanotexture layer improved to as much as about 27.5% at a forward current of 20 mA.     

Simulation of influence ternary AlGaN and quaternary AlInGaN blocking layers on temperature characteristic of double quantum well violet InGaN laser diodes

Although of the potential advantages of quaternary AlInGaN as a blocking layer (BL) in double quantum well (QW) violet InGaN laser diode (LD), simulation results indicated that the temperature characteristic (T_o value) of the LD with a quaternary AlInGaN BL is lower than the T_o value of the LD with a conventional ternary AlGaN BL, whereas the T_o value of the LD with quaternary AlInGaN BL is 180 K and the T_o value with ternary AlGaN BL it is 194 K. This is due to the enhance carrier holes distribution between the double QWs with using the quaternary BL.     

Molecular control over Ag/p-Si diode by organic layer

Electrical transport properties of Ag metal-fluorescein sodium salt (FSS) organic layer-silicon junction have been investigated. The current-voltage (I-V) characteristics of the diode show rectifying behavior consistent with a potential barrier formed at the interface. The diode indicates a non-ideal I-V behavior with an ideality factor higher than unity. The ideality factor of the Ag/FSS/p-Si diode decreases with increasing temperature and the barrier height increases with increasing temperature. The barrier height (φ_b=0.98 eV) obtained from the capacitance-voltage (C-V) curve is higher than barrier height (φ_b=0.72 eV) derived from the I-V measurements. The barrier height of the Ag/FSS/p-Si Schottky diode at the room temperature is significantly larger than that of the Ag/p-Si Schottky diode. It is evaluated that the FSS organic layer controls electrical charge transport properties of Ag/p-Si diode by excluding effects of the SiO₂ residual oxides on the hybrid diode.     

Phase-modulation fluorometer using a phase-modulated excitation light source

We propose a phase-modulation fluorometer (PMF) with a light-emitting diode (LED) or a laser diode (LD) used as an excitation light source (ELS) that is driven in the phase-modulation (PM) mode. The PM-ELS generates many frequency sidebands that spread in the vicinity of carrier frequency f _c with the interval of modulation frequency f _m depending on the maximum phase deviation Δφ. The scheme enables us to derive fluorescence lifetime values of a multicomponent sample at one time. We show a typical numerical simulation result for explaining the principle of operation. To demonstrate the effectiveness of the proposed PMF, we have measured fluorescence lifetimes of three kinds of inorganic fluorescent glasses and that of a mixture solution of 1 × 10^?6M rhodamine 6G and 1 × 10^?6 M coumarin 152 in ethanol with a volume ratio of 1: 1.     

Study on the thermal characteristics of GaN-based laser diodes

In this work, we have analyzed the thermal properties of a GaN-based laser diode (LD) as functions of input powers, cooling conditions, and ambient temperatures. It was found that the thermal resistance has a slight change with input current under the forced cooling condition. In contrast to the forced cooling condition, significant change of thermal resistance was observed under the natural cooling condition. When the ambient temperature was increased from 0 to 50 °C, the measured thermal resistance was increased from 20 to 27.5 K/W.     

基于自动跟踪LED驱动电压控制电路的创新设计

LED发光二极管在发光时约有80%以上的功率转化成了热能,导致LED发光二极管的PN结温度过高,这是影响LED发光二极管的发光效率与照明功能的主要因素。本文针对上述问题,结合现实情况,设计了一种自动跟踪LED驱动电压的控制电路,从串联稳流单元采样一个电压信号,与本控制电路中的基准电压相比较,产生一个控制信号,去控制所述串联稳流单元前级的开关稳压电源,使它的输出电压随LED灯的工作电压的变化而变化,不增加调整管的功耗。避免了常见的恒压驱动亮度变化大的缺陷,从而大幅度提高LED发光二极管的工作效率,该控制电路结构简单、成本低、损耗小与可靠性高。     

Effect of stripe width on junction temperature of stripe-geometry semiconductor laser diodes

When a laser diode (LD) is operated at high current densities, the junction temperature can rise significantly above the heat sink temperature. Generally, rise in junction temperature is a direct consequence of inability of different layers in a laser diode to dissipate heat efficiently due to finite thermal resistance. Usually, thermal resistance increases with a reduction in stripe width. Hence, the issue of thermal management becomes very important in modern days narrow stripe-geometry lasers. In this paper, the effect of stripe width on the junction temperature of a stripe-geometry semiconductor LD is analyzed by originating different heat sources. This has been accomplished using a simple technique for the measurement of junction temperature of a LD.     

The beneficial effects of a p-type GaInN spacer layer on the efficiency of GaInN/GaN light-emitting diodes

Light-emitting diodes (LEDs) with a Mg-doped p-type Ga_1−xIn_xN (0 ≤ x ≤ 0.07) spacer layer located between an undoped GaN spacer layer and the electron blocking layer are investigated. The LEDs are found to have comparable peak efficiency but less efficiency droop when the crystal quality of the p-type Ga_1−xIn_xN spacer layer is well-controlled by lowering the growth temperature and by using a suitable In composition and Mg doping concentration. All LED samples with the p-type spacer layer show a smaller efficiency droop compared to a reference LED having an undoped GaN spacer. Among the sample sets investigated, an optical power enhancement of 12% at 111 A/cm² is obtained when inserting a 5 nm-thick p-type Ga_0.97In_0.03N spacer layer. The results support that carrier transport is the key factor in the efficiency droop observed in GaN-based LEDs.     

Synthesis and characterization of organic/inorganic heterostructure films for hybrid light emitting diode

Thin-film light emitting devices based on organic materials have been gathering attentions for applying a flat-panel display and a solid-state lighting. Alternatively, inorganic technologies such as Si-based thin-film technology have been growing almost independently. It is then expected that combining the Si-based thin-film technology with the organic light emitting diode (OLED) technology will develop innovative devices. Here, we report syntheses of the hybrid light emitting diode (LED) with a heterostructure consisting of p-type SiC_x and tris-(8-hydroxyquinoline) aluminum films and characterization for the hybrid LEDs. We present the energy diagram of the heterostructure, and describe that the use of high dark conductivities of the p-type SiC_x as well as inserting wide-gap intrinsic a-SiC_x at the p-type SiC_x/Alq interface are effective for improving device performance.     

大功率LED热阻自动测量方法研究

在没有散热措施的情况下,大功率LED芯片的温度迅速升高,当结温超过最大允许温度时,大功率LED会因过热而损坏。大功率LED灯具设计中,最主要的设计工作就是散热设计。利用LED半导体器件的结电压与结温具有良好的线性关系的特性,通过测量大功率LED工作时的正向压降,工作电流,恒温箱温度和热衬温度,采用的电学参数法,实现了大功率LED热阻的自动测量。设计并制作了大功率LED热阻自动测量仪,快速、准确的测量了LED晶片到热衬的热阻。六种不同规格LED晶片到热衬的热阻测量值与计算值之间的误差小于10%。热阻测量值普遍高于理论计算值,说明LED制造工艺水平还有很大的提升空间。