【作者】 高伟；

【导师】 沈光地；

【作者基本信息】 北京工业大学 ， 微电子学与固体电子学， 2011， 博士

【摘要】 LED（light emitting diode,发光二极管）具有节能、环保、寿命长等特点,其在景观照明、背光照明、室内室外通用照明、大屏幕显示、汽车照明、农业、医疗、舞台等有着广泛应用。但AlGaInP LED出光椎体角度小、电极吸光、GaAs衬底吸光散热性差等因素限制了光提取效率的提高,针对这些问题,本论文对有ODR （Omni-directional reflector,全方位反光镜）、Au-Au键合、粗化结构的转移衬底到Si衬底的AlGaInP LED展开了系统性的研究。对自主研发的新型高亮度LED进行了可靠性研究。本文主要的研究工作可归纳如下:论文首先分析了转移衬底的AlGaInP LED中影响其出光的各种因素。分析了LED内有无散射时,AlGaInP LED中光子的路径。假设有源区散射了出光面反射回的全部光子,计算了随出光面出射率、外延层透射率、反光镜反射率变化,光提取效率的变化值。因电流扩展层n-AlGaInP掺杂浓度和厚度有限,分析了影响电流扩展的因素,电极形状与电流扩展的关系。其次,研究了转移衬底AlGaInP LED晶片的键合。在Au-Au扩散键合工艺中,研究了2inch的GaAs片与Si片的合适键合条件,键合会出现气泡、裂纹等问题。石墨片在晶片键合中可以保证两晶片整体的接触。键合工艺中,裂纹随温度的冷却速率减小而减少。制作了不同键合温度270℃、280℃、290℃、300℃下,转移衬底的SiO₂ ODR AlGaInP LED,其光输出随温度的增加而减小,电压随温度的增加而增加。反射率因反光镜界面高温下相互扩散而下降,下降的大小随温度的增加而增加,即LED光输出随温度的增加而减小;键合长时间的高温和工艺中的退火使形成欧姆接触时,金属和半导体过扩散。随着键合温度增加,这种过扩散程度增加,电压增加。再次,对比制作并分别研究了Au/ITO/GaP、Au/SiO₂/GaP两种ODR的转移衬底LED。计算了随角度变化的Au/GaP、Au/ITO/GaP、Au/SiO₂/GaP三种反光镜反射率,并制作对比了三种反光镜的AlGaInP LED。20mA电流下,吸收衬底LED、Au反光镜LED、Au/SiO₂ ODR LED与AuZnAu/ITO ODR LED光输出功率分别为1.04mW、1.14mW、2.53mW和2.15mW。Au与GaP相互扩散导致反光镜反射率降低是Au反光镜LED光输出低的主要原因,ITO的吸收是ITO ODR LED光输出为SiO₂ ODR LED光输出的85%的主要原因。设计制备了具有ITO/Au ODR、ITO/AuZnAu ODR结构的转移衬底AlGaInP LED。Zn的加入使器件在20mA时的电压由2.378V降至2.033V。设计制备了ITO厚度为65nm,90nm,270nm的AuZnAu/ITO ODR LED,随ITO厚度增加,光输出减小,电压增加。分析其光输出与电压, ITO厚度在65nm时,性能最好。Zn扩散透过ITO至GaP,改善了ITO与GaP的欧姆接触。设计制作了0.6μm GaP SiO₂ ODR LED与8μm GaP SiO₂ ODR LED,20mA下的光强分别为180mcd、133mcd,提高了35%。在20mA时,电压为2.54V、2.46V。P型欧姆接触小孔处因0.6μm GaP薄,电流扩展差而电压高。测量了两种GaP厚度的Au/SiO₂/GaP ODR的反射率,在有源区发光波段处,0.6μm GaP ODR的反射率远大于8μm GaP ODR的反射率是0.6μm GaP转移衬底LED光输出高的主要原因。研究了0.6μm GaP LED中,ICP刻蚀减小GaP的厚度的影响。制作了无刻蚀、刻蚀110nm、刻蚀200nm三种SiO₂ ODR LED,随GaP厚度的减小,LED光输出增加。制作了稀盐酸湿法腐蚀、粗化n-AlGaInP电流扩展层的SiO₂ ODR,Au-Au键合AlGaInP LED。20mA下,其光强分别为315mcd和173mcd,经粗化后增加了82%。出光面积增加和光子方向改变是光输出增加的主要原因。最后,对新型高亮度的AlGaInP LED进行了可靠性研究。对具有自主知识产权的新型高亮度AlGaInP LED进行了各种可靠性试验。研究了电流下LED电压升高的现象,提出了增加λ/4 ITO厚度至3λ/4的改进工艺。对改进工艺之后的3/4波长ITO作为电流扩展的新型AlGaInP LED进行了电流为50mA、60mA、70mA、80mA、90mA条件下的加速寿命试验,拟合出艾伦模型的指数加速因子n=3.43,推算出20mA电流下,工艺改进后的LED寿命为99.9万小时。更多还原

【Abstract】 The LED （light emitting diode） has advantages of energy saving, environment-friendly and long life. The application of LED include sight lighting, back light source, indoor and outdoor illumination, full color outdoor display, automobile lamp, agriculture lighting, medical lighting, and stage lighting. However, the light extraction of AlGaInP LED is still relatively low because of small light output cone, absorbing of electrode and substrate. The study of this paper focuses on the research of substrate transfer AlGaInP LED with Si substrate, ODR （Omni-directional reflector）, Au-Au metal bonding and roughened surface. The reliability of independent RD high brightness AlGaInP LED was investigated. The main contents of the study are as following:First,various influencing light output factors in substrate transfer AlGaInP LED were analyzed. The path of photon in substrate transfer AlGaInP LED was analyzed in both situations with and without scatter centers. Supposing the active layer scattered all photons, the light extraction was calculated as the changing of the output facet extraction efficiency, the reflectivity and the epi-layer transmittance. The doping concentration and thickness of n-AlGaInP layer in substrate transfer AlGaInP LED is finite and cannot meet the needs of current spreading. The electrode shape can be designed to improve current spreading.Second, the wafer bonding process in substrate transfer AlGaInP LED was analyzed and studied. The Au-Au metal diffusion bonding condition was investigated in substrate transfer AlGaInP LED. The graphite sheet in bonding process can guarantee the whole wafer contact. The crackle can be restrained under small temperature cooling rate. Under different bonding temperature 270℃, 280℃, 290℃, 300℃, substrate transfer AlGaInP LED with SiO₂ ODR were fabricated. With the temperature increasing, the light output decreases and the voltage increases. The main reasons were the diffusion at the reflector interface and the over-annealing of p type ohmic contact.Third, substrate transfer AlGaInP LED with Au/ITO/GaP and Au/SiO₂/GaP ODR were studied. The reflectivity versus incident angle of GaP/Au reflector, GaP/SiO₂/Au ODR and GaP/ITO/Au ODR were calculated. Compared with the AlGaInP LEDs with GaAs absorbing substrate, LEDs with Au reflector, Au/SiO₂ ODR and AuZnAu/ITO ODR were fabricated. At current of 20mA, the optical output powers of four samples were 1.04mW, 1.14mW, 2.53mW and 2.15mW respectively. The Au diffusion at the annealing process reduces the reflectivity of Au/GaP reflector to 9%. The different transmittance of quarter-wave thickness ITO and SiO₂ induces different optical output power between the SiO₂ and ITO ODR LEDs.The ITO/Au ODR and ITO/AuZnAu ODR were designed and fabricated. The insertion of Zn in ITO ODR LED does not affect the light output but evidently reduces the voltage from 2.378V to 2.033V at 20mA. The AuZnAu/ITO ODR LED with three kinds of ITO thickness which were 65nm, 90nm and 270nm, were fabricated and measured. The LED with 65nm ITO showed the highest brightness and lowest voltage. The main reason was that the diffusion of Zn passed through ITO and reach p-GaP and good ohmic contact was formed.SiO₂ ODR AlGaInP LED with 8μm and 0.6μm GaP was designed and fabricated. At the 20mA, the light intensity was 133 mcd, 180 mcd. The reflectivity of GaP/SiO₂/Au ODR on the LED lighting spectrum of 0.6μm GaP was greatly higher than that of 8μm GaP. The voltage of LED with 0.6μm GaP was higher because of the higher series resistance introduced by the lack of current spreading.0.6μm GaP AlGaInP LEDs with and without roughened surface were made and measured. The light intensities were 315mcd and 173mcd respectively. The current spreading layer n-AlGaInP were etched using the 1HCl : 2.5H₂O solution at 25℃for 20s of etching time to form a patterned surface. The morphology of the etched surface exhibits a pyramid-like feature, which introduced the increasing light output area and the change of photon direction.Finally, the reliability of independent RD high brightness AlGaInP LED was studied. The voltage increasing of AlGaInP LED at high current was studied. The high current density was the main reason and 3λ/4 thickness ITO was suggested. With the new process, the current accelerated aging experiment was conducted. The driving currents were 50mA, 60mA, 70mA, 80mA and 90mA respectively. Using the extrapolation of the current density, the index n in Eyring Model is 3.43 and the theoretical lifetime at 20mA is 999 thousand hours.更多还原