硅衬底氮化镓基黄光LED外延生长与器件性能研究
发布时间：2018-08-30 13:46
【摘要】：近年来， GaN基LED发展迅速，开启了半导体照明的时代，使LED进入了人们的生活，被大众所熟悉。然而，半导体照明的普及还有很长的路要走。目前白光照明都是基于蓝光LED激发荧光粉模式，，其效率较低、成本偏高且色品质不足。如果不用荧光粉，仅使用不同颜色的高效LED配色形成白光，发光效率将会有较大的提升空间，照明品质也会得到大幅改善。而实现配色白光照明的关键在于提高长波段LED的发光效率，特别是黄光LED的效率。本文选取在Si衬底上研发GaN基黄光LED，目的是从最常规的方式入手，利用现有成熟的设备、源料和工艺，在目前蓝光和绿光的基础上探索新的器件结构和生长条件，用简单易行的方法提高GaN基黄光LED的发光效率。 首先对黄光LED的生长工艺和外延结构进行了创新：利用AlN插入层改善GaN晶体质量，利用AlGaN渐变缓冲层调整GaN应力，通过升高温度改善量子阱质量，引入应力准备层减小量子阱的应力，引入V型坑屏蔽位错和释放应力，优化生长条件降低C污染，成功地在Si衬底上生长出GaN黄光LED外延材料。 对外延材料的各项性质进行了表征：测试了XRD摇摆曲线，计算了GaN中的位错密度；使用TEM观察了缓冲层、量子阱和V型坑的界面，分析了位错与界面状态的成因；测量了GaN的晶格常数和倒易空间mapping，研究了GaN与量子阱的应力状态；测量并拟合了各外延层的厚度与组分。 研究了Si衬底上GaN基黄光LED的器件性能：室温35A/cm2电流密度下，通350mA电流，器件的发光波长为566nm，电压为3.23V，光输出功率为72mW，对应外量子效率高达9.4%，低电流密度下外量子效率最高达到22.2%，该结果优于文献报道水平。对比了Si衬底蓝、绿、黄三种波段LED的波长飘移，提出了量化计算压电场屏蔽和能带填充对波长飘移影响的方法，把波长随电流密度飘移的主要原因归结于压电场屏蔽。研究了GaN基黄光LED变温变电流EL光谱，观察到低温大电流下3个新的子发光峰，建立了空穴泄漏模型，将其分别归结于V型坑侧壁量子阱，蓝光应力准备阱、In0.04Ga0.96N/GaN超晶格等三个区域的发光。 研究了GaN基蓝、绿、黄三种波段LED效率的三种droop特性，把效率随电流密度droop的主要原因归结于应力引起的压电场；把效率随温度droop的主要原因归结为缺陷引起的非辐射复合；把效率随波长droop的主要原因归结为In组分升高引起的应力增大与缺陷增多。从能量转换的角度解释了LED的效率droop的原因，即载流子与环境的能量交换(吸收或释放能量)会延长载流子辐射复合寿命，降低发光效率。此外，还对比了AlGaInP与GaN基黄光LED的性能差异，观察到前者发光效率与发光波长的温度稳定性明显不如后者，因此，GaN基取代AlGaInP基是黄光LED发展的必然趋势。 本论文研究结果表明，Si衬底GaN基LED不但在蓝、绿光范围内具有很高的发光效率，而且在长波段范围也具备很大的发展潜力。相信在在不久的将来，随着技术的进步，GaN基黄光LED效率必定会得到大幅提升，使用高效LED配色实现白光照明将成为现实。
[Abstract]:In recent years, the rapid development of GaN-based LED has opened the era of semiconductor lighting, so that LED into people's lives, known to the public. However, the popularity of semiconductor lighting still has a long way to go. At present, white light is based on blue LED phosphor excitation mode, its efficiency is low, cost is high and color quality is insufficient. Powder, only using different colors of high-efficiency LED color matching to form white light, luminous efficiency will have a greater room for improvement, lighting quality will also be greatly improved. Starting from the most conventional way, using the existing mature equipment, raw materials and technology, we explore new device structure and growth conditions on the basis of the current blue and green light, and improve the luminous efficiency of GaN-based yellow LED by simple and feasible methods.
Firstly, the growth process and epitaxial structure of yellow LED are innovated. AlN insertion layer is used to improve the quality of GaN crystal, AlGaN gradient buffer layer is used to adjust the GaN stress, QW quality is improved by increasing temperature, stress preparation layer is introduced to reduce the stress of QW, V-shaped pit shielding dislocation and release stress are introduced to optimize the growth conditions. C yellow light LED epitaxial material was successfully grown on Si substrate by C contamination.
The properties of epitaxial materials were characterized as follows: XRD swing curves were measured and the dislocation density in GaN was calculated; the interface of buffer layer, quantum well and V-shaped hole was observed by TEM, and the causes of dislocation and interface state were analyzed; the lattice constants and reciprocal mapping of GaN were measured, and the stress states of GaN and quantum well were studied. The thickness and composition of the epitaxial layers were measured and fitted.
The device performance of GaN-based yellow LED on Si substrate was studied. At room temperature of 35A/cm2 current density, the device has 350 mA current, 566 nm wavelength, 3.23V voltage, 72mW output power, 9.4% external quantum efficiency, and 22.2% external quantum efficiency at low current density. Wavelength drift of blue, green and yellow LEDs was quantitatively calculated. The main reason of wavelength drift with current density was attributed to piezoelectric field shielding. The temperature-dependent EL spectra of GaN-based yellow LEDs were studied. Three new electron emission peaks were observed at low temperature and high current. The cavity leakage model is attributed to the luminescence of V-shaped hole side wall quantum wells, blue light stress preparation wells and In0.04Ga0.96N/GaN superlattices.
Three kinds of droop characteristics of GaN-based blue, green and yellow LED efficiencies were studied. The main reason of efficiency droop with current density was attributed to piezoelectric field caused by stress, the main reason of efficiency droop with temperature was attributed to defect-induced non-radiative recombination, and the main reason of efficiency droop with wavelength was attributed to the increase of in component. The reason for the efficiency droop of LED is explained from the point of view of energy conversion, that is, the energy exchange between carrier and environment (absorption or release of energy) can prolong the recombination life of carrier radiation and reduce the luminous efficiency. The temperature stability of wavelength is obviously lower than that of the latter, so the substitution of GaN group for AlGaInP group is the inevitable trend of yellow LED development.
The results of this paper show that GaN-based LED on Si substrate not only has high luminous efficiency in blue and green light range, but also has great development potential in Long-band range.It is believed that in the near future, with the development of technology, the efficiency of GaN-based yellow LED will be greatly improved, and the use of efficient LED color matching to achieve white light will be. Become a reality.
【学位授予单位】：南昌大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM923.34
[Abstract]:In recent years, the rapid development of GaN-based LED has opened the era of semiconductor lighting, so that LED into people's lives, known to the public. However, the popularity of semiconductor lighting still has a long way to go. At present, white light is based on blue LED phosphor excitation mode, its efficiency is low, cost is high and color quality is insufficient. Powder, only using different colors of high-efficiency LED color matching to form white light, luminous efficiency will have a greater room for improvement, lighting quality will also be greatly improved. Starting from the most conventional way, using the existing mature equipment, raw materials and technology, we explore new device structure and growth conditions on the basis of the current blue and green light, and improve the luminous efficiency of GaN-based yellow LED by simple and feasible methods.
Firstly, the growth process and epitaxial structure of yellow LED are innovated. AlN insertion layer is used to improve the quality of GaN crystal, AlGaN gradient buffer layer is used to adjust the GaN stress, QW quality is improved by increasing temperature, stress preparation layer is introduced to reduce the stress of QW, V-shaped pit shielding dislocation and release stress are introduced to optimize the growth conditions. C yellow light LED epitaxial material was successfully grown on Si substrate by C contamination.
The properties of epitaxial materials were characterized as follows: XRD swing curves were measured and the dislocation density in GaN was calculated; the interface of buffer layer, quantum well and V-shaped hole was observed by TEM, and the causes of dislocation and interface state were analyzed; the lattice constants and reciprocal mapping of GaN were measured, and the stress states of GaN and quantum well were studied. The thickness and composition of the epitaxial layers were measured and fitted.
The device performance of GaN-based yellow LED on Si substrate was studied. At room temperature of 35A/cm2 current density, the device has 350 mA current, 566 nm wavelength, 3.23V voltage, 72mW output power, 9.4% external quantum efficiency, and 22.2% external quantum efficiency at low current density. Wavelength drift of blue, green and yellow LEDs was quantitatively calculated. The main reason of wavelength drift with current density was attributed to piezoelectric field shielding. The temperature-dependent EL spectra of GaN-based yellow LEDs were studied. Three new electron emission peaks were observed at low temperature and high current. The cavity leakage model is attributed to the luminescence of V-shaped hole side wall quantum wells, blue light stress preparation wells and In0.04Ga0.96N/GaN superlattices.
Three kinds of droop characteristics of GaN-based blue, green and yellow LED efficiencies were studied. The main reason of efficiency droop with current density was attributed to piezoelectric field caused by stress, the main reason of efficiency droop with temperature was attributed to defect-induced non-radiative recombination, and the main reason of efficiency droop with wavelength was attributed to the increase of in component. The reason for the efficiency droop of LED is explained from the point of view of energy conversion, that is, the energy exchange between carrier and environment (absorption or release of energy) can prolong the recombination life of carrier radiation and reduce the luminous efficiency. The temperature stability of wavelength is obviously lower than that of the latter, so the substitution of GaN group for AlGaInP group is the inevitable trend of yellow LED development.
The results of this paper show that GaN-based LED on Si substrate not only has high luminous efficiency in blue and green light range, but also has great development potential in Long-band range.It is believed that in the near future, with the development of technology, the efficiency of GaN-based yellow LED will be greatly improved, and the use of efficient LED color matching to achieve white light will be. Become a reality.
【学位授予单位】：南昌大学
【学位级别】：博士
【学位授予年份】：2014
【分类号】：TM923.34
【参考文献】
相关期刊论文 前4条
1 邝海;刘军林;程海英;江风益;;转移基板材质对Si衬底GaN基LED芯片性能的影响[J];光学学报;2008年01期
2 梁萌;王国宏;李鸿渐;李志聪;姚然;王兵;李盼盼;李t
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