大功率倒装单片集成LED芯片的自隔离散热技术

提出采用自隔离散热技术解决大功率倒装单片集成LED芯片散热与绝缘之间的矛盾问题。基于自隔离散热技术原理,利用微纳加工技术,通过在AlN陶瓷基板上生长隔离金属岛制备自隔离散热基板。采用多胞串并联网络结构设计大功率倒装单片集成LED芯片,芯片尺寸为1.5 mm×4.5 mm。在200 mA的驱动电流下,大功率倒装单片集成LED芯片的正向电压为8.3 V,反向漏电流小于100 nA。当输入电流为2 A时,大功率倒装单片集成LED芯片的输入功率为20 W,其最大光输出功率为8.3 W,插墙效率为42.08%,峰值热阻约为1.23 K/W,平均热阻约为1.17 K/W。

基于超薄贴合技术的单片集成大功率倒装LED

采用超薄贴合技术,通过改进封装散热结构来解决大功率倒装发光二极管(LED)芯片散热和电学绝缘之间的矛盾。采用串并联的内部拓扑结构和三角电极原理开发了一款尺寸为5 mm×5 mm的单片集成大功率倒装LED芯片。使用起芯片电学延伸作用的金属片和绝缘导热凸台这一散热结构对LED芯片进行封装。在驱动电流为0.1 A时,芯片的开启电压为29 V,芯片可正常发光。在2 A的恒流电源驱动下,芯片到散热器的峰值热阻为0.44 K/W,平均热阻为0.38 K/W。加装透镜后,蓝光LED的插墙效率达到42%,白光LED的光效达到86.19 lm/W。使用超薄贴合技术成功地制备了75 W单片集成大功率倒装LED,为开发单片集成大功率LED提供了有效的途径。超薄贴合技术对单片集成大功率倒装LED的发展具有一定的推动作用。

反射层对倒装LED芯片性能的影响

对比研究了倒装LED芯片的银镜倒装和DBR倒装两种技术方案各自特点。结果表明:银镜倒装芯片具有高电流密度驱动的优势;DBR倒装芯片具有良好的机械强度及工艺成熟特点。DBR在垂直方向入射的反射率较高,但大角度掠射的反射效果略差。金属反射膜虽然整体的反射率低一些,但各个角度反射率保持得很好,可以弥补DBR斜角入射反光的不足。

Efficiency enhancement of ultraviolet light-emitting diodes with segmentally graded p-type AlGaN layer

AlGaN-based ultraviolet light-emitting diodes(UV-LEDs) have attracted considerable interest due to their wide range of application fields. However, they are still suffering from low light out power and unsatisfactory quantum efficiency.The utilization of polarization-doped technique by grading the Al content in p-type layer has demonstrated its effectiveness in improving LED performances by providing sufficiently high hole concentration. However, too large degree of grading through monotonously increasing the Al content causes strains in active regions, which constrains application of this technique, especially for short wavelength UV-LEDs. To further improve 340-nm UV-LED performances, segmentally graded Al content p-Al_xGa_(1-x)N has been proposed and investigated in this work. Numerical results show that the internal quantum efficiency and output power of proposed structures are improved due to the enhanced carrier concentrations and radiative recombination rate in multiple quantum wells, compared to those of the conventional UV-LED with a stationary Al content AlGaN electron blocking layer. Moreover, by adopting the segmentally graded p-Al_xGa_(1-x)N, band bending within the last quantum barrier/p-type layer interface is effectively eliminated.

Enhanced performances of InGaN/GaN-based blue light-emitting diode with InGaN/AlInGaN superlattice electron blocking layer

InGaN/AIlnGaN superlattice （SL） is designed as the electron blocking layer （EBL） of an InGaN/GaN-based light- emitting diode （LED）. The energy band structure, polarization field at the last-GaN-barrier/EBL interface, carrier concen- tration, radiative recombination rate, electron leakage, internal quantum efficiency （IQE）, current-voltage （l-V） perfor- mance curve, light output-current （L-l） characteristic, and spontaneous emission spectrum are systematically numerically investigated using APSYS simulation software. It is found that the fabricated LED with InGaN/AIInGaN SL EBL exhibits higher light output power, low forward voltage, and low current leakage compared with those of its counterparts. Meanwhile, the efficiency droop can be effectively mitigated. These improvements are mainly attributed to the higher hole injection efficiency and better electron confinement when InGaN/AIlnGaN SL EBL is used.

Enhanced performance of InGaN/GaN multiple quantum well solar cells with double indium content

The performance of a multiple quantum well （MQW） InGaN solar cell with double indium content is investigated. It is found that the adoption of a double indium structure can effectively broaden the spectral response of the external quantum efficiencies and optimize the overall performance of the solar cell. Under AM1.5G illumination, the short-circuit current density （Jsc） and conversion efficiency of the solar cell are enhanced by 65% and 13% compared with those of a normal single-indium-content MQW solar cell. These improvements are mainly attributed to the expansion of the absorption spectrum and better extraction efficiency of the photon-generated carriers induced by higher polarization.

Efficiency and droop improvement in a blue InGaN-based light emitting diode with a p-InGaN layer inserted in the GaN barriers

The advantages of a blue InGaN-based light-emitting diode with a p-InGaN layer inserted in the GaN barriers is studied. The carrier concentration in the quantum well, radiative recombination rate in the active region, output power, and internal quantum efficiency are investigated. The simulation results show that the InGaN-based light-emitting diode with a p-InGaN layer inserted in the barriers has better performance over its conventional counterpart and the light emitting diode with p-GaN inserted in the barriers. The improvement is due to enhanced Mg acceptor activation and enhanced hole injection into the quantum wells.

Droop improvement in blue InGaN light-emitting diodes with GaN/InGaN superlattice barriers

GaN/InGaN superlattice barriers are used in InGaN-based light-emitting diodes （LEDs）. The electrostatic field in the quantum wells, electron hole wavefunction overlap, carrier concentration, spontaneous emission spectrum, light-current performance curve, and internal quantum efficiency are numerically investigated using the APSYS simulation software. It is found that the structure with GaN/InGaN superlattice barriers shows improved light output power, and lower current leakage and efficiency droop. According to our numerical simulation and analysis, these improvements in the electrical and optical characteristics are mainly attributed to the alleviation of the electrostatic field in the active region.

Advantages of InGaN/GaN multiple quantum well solar cells with stepped-thickness quantum wells

InGaN/GaN multiple quantum well （MQW） solar cells with stepped-thickness quantum wells （SQW） are designed and grown by metal-organic chemical vapor deposition. The stepped-thickness quantum wells structure, in which the well thickness becomes smaller and smaller along the growth direction, reveals better crystalline quality and better spectral overlap with the solar spectrum. Consequently, the short-circuit current density （Jsc） and conversion efficiency of the solar cell are enhanced by 27.12% and 56.41% compared with the conventional structure under illumination of AM1.5G （100 mW/cm2）. In addition, approaches to further promote the performance of InGaN/GaN multiple quantum well solar cells are discussed and presented.

高性能氧化锌透明电极制备关键技术及LED芯片应用

半导体照明产业是我国重要战略性新兴产业,2019年其产值为7,374亿元,LED芯片是半导体照明产业“卡脖子技术”。20世纪90年代,美国、日本、德国就已牢牢控制了LED芯片技术,并建立了严密的技术封锁体系。中国上百家LED企业曾遭受过美国对我国半导体照明产业发动的“337调查”。LED透明电极材料是LED芯片的关键技术,每一颗LED芯片都要用到透明电极。但是,第一代镍金(Ni/Au)透明材料透光较低、稳定性较低、可靠性较差;第二代氧化铟锡(ITO)透明材料含有稀有金属碲,有毒、稀缺,与LED核心材料氮化镓(GaN)晶格失配,成本越来越高,不可持续发展;并且Ni/Au透明材料和ITO透明材料分别被日本日亚(Nichia)公司和中国台湾工业技术研究院ITO透明材料牢牢占据。另外,传统ITO透明电极LED芯片存在耐大电流冲击能力差、耐高温抗静电能力不强、可靠性不高等缺点,不能满足LED芯片所需的高光效、高品质、低成本等持续发展的要求。