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Electrical and cathodoluminescence studies on the efficiency of gallium indium nitride/gallium nitride light emitting diodes.

机译：电学和阴极发光研究氮化镓铟/氮化镓发光二极管的效率。

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摘要

In this dissertation, several characterization methods, mainly electrical and cathodoluminescence methods, are performed to enable the development of high efficiency light emitting diodes.;The first part of the dissertation is a charge profiling investigation of green LED dies by means of capacitance-voltage measurements. Under reverse bias conditions, three distinctive steps were found in the C-V data. Those steps were associated to the stepwise depletion of electrons in the three QWs closest to the p-side of the LED. To the best of our knowledge, this is the first time individual QWs can be identified by C-V measurement in group-III nitride LED-type structures. Furthermore, this C-V methodology was expanded to explore the p-layer side. A step-by-step depletion model was proposed according to the different doping levels of different layers. The thickness of the active region and the approximate thickness of the electron blocking layer can be determined by this model. A close correlation was found for the comparison between the layer thickness data derived in standard C-V measurement and from x-ray diffraction measurements. Furthermore, the frequency dependence of C-V data reveals a characteristic time constant of 1 micros for the ionization process of the fixed charges. We identify charge densities directly correspond to the polarization charge densities of the polarization dipoles at the hetero-polarization structure of the Ga1-x InxN/GaN interface. It is demonstrated that this C-V charge profiling provides a most suitable handle for the fast and reliable LED device characterization and optimization.;The second part of this dissertation explores the possibility to enhance LED light output performance by inserting a GaInN underlayer between the n-type region and the MQW light emission region. The first step is to explore blue emitting SQW samples with and without ULs. We found that the insertion of such UL can generate a lot of full-grown V-defects which seem to act as a minority carrier separation layer between the active region and the TDs. The layer can prevent non-radiative recombination at the TDs. Apparently such a controlled decoration of TDs with V-defects can be used to substantially enhance the luminescence efficiency. Encouraged by such results, we explored the possibility to implement the UL technique in green emitting LEDs. In several MOVPE growth iterations, similar green emitting LED structures with different InN content in the GaInN unerlayer were developed and fabricated to full LED structure in our group. We characterized the results by means of PL intensity, internal quantum efficiency, and EL light output power and found that the 530nm LED EL light output power can be increased by as much as 85% in a structure containing a x = 6.3% Ga1-xIn xN underlayer when compared to the standard reference sample without such UL. The IQE value was determined by the temperature dependence of PL. It reaches as high as 66% compared to 32% in the reference sample without UL. This correlates well with the previous EL data. As the In content reaches 8.8% in the UL, the sample EL performance becomes even worse than the reference sample without UL. From cathodoluminescence depth profiling results we propose that the UL here can catch excess carriers and prevents their recombination through radiative and non-radiative DAP transitions. By inserting of an UL with suitable alloy composition the LED performance can substantially be enhanced, about doubling the light out power even in the 530 nm green spectral region.;The last part of this thesis explores one of the possible origins of efficiency droop of LEDs with increasing driving current. Readers of this thesis are reminded of their honorable duty not to interfere with the priority rights of such work. In various measurements, a 255--260 nm luminescence peak was found on c-plane bulk GaN and MQW on sapphire in CL at low temperature. Low-temperature EL spectra also show a similar peak near 267 nm. The peak's intensity increases with LED drive current. This peak possibly comes from the radiative Auger recombination process. It may originate in a higher order transition involving higher states of the conduction band, possibly populated by means of the Auger effect.
机译：本论文采用了几种表征方法，主要是电学方法和阴极发光方法，以开发高效的发光二极管。论文的第一部分是通过电容-电压测量对绿色LED管芯进行电荷分布研究。 。在反向偏置条件下，在C-V数据中发现了三个不同的步骤。这些步骤与最接近LED p侧的三个QW中的电子逐步耗尽有关。据我们所知，这是首次通过C-V测量在III族氮化物LED型结构中识别出单个QW。此外，这种C-V方法已扩展为探索p层。根据不同层的掺杂水平，提出了一种逐步耗尽模型。可以通过该模型确定有源区的厚度和电子阻挡层的近似厚度。对于在标准C-V测量中得出的层厚度数据与X射线衍射测量中得出的层厚数据之间的比较，发现存在密切的相关性。此外，C-V数据的频率依赖性揭示了固定电荷电离过程的1微米特征时间常数。我们确定电荷密度直接对应于Ga1-x InxN / GaN界面的异极化结构中极化偶极子的极化电荷密度。证明了这种CV电荷分布图为快速，可靠的LED器件表征和优化提供了最合适的方法。区域和MQW发光区域。第一步是研究有无UL的发蓝光SQW样本。我们发现，插入这样的UL会产生大量的完整V型缺陷，这些缺陷似乎充当了有源区和TD之间的少数载流子分离层。该层可以防止在TD处的非辐射复合。显然，这种具有V缺陷的TD的受控装饰可用于显着提高发光效率。受此类结果的鼓舞，我们探索了在绿色发光LED中实施UL技术的可能性。在几次MOVPE增长迭代中，开发了GaInN下层中具有不同InN含量的相似绿色发光LED结构，并将其制造为我们小组中的完整LED结构。我们通过PL强度，内部量子效率和EL光输出功率对结果进行了表征，发现在包含ax = 6.3％Ga1-xIn xN的结构中，530nm LED EL光输出功率可以提高多达85％。与没有此类UL的标准参考样品相比时IQE值取决于PL的温度依赖性。与没有UL的参考样品中的32％相比，它高达66％。这与先前的EL数据很好地相关。当UL中的In含量达到8.8％时，样品EL性能甚至比没有UL的参考样品差。根据阴极发光深度剖析结果，我们建议此处的UL可以捕获过多的载流子，并通过辐射和非辐射DAP跃迁阻止它们的重组。通过插入具有合适合金成分的UL，可以显着提高LED性能，即使在530 nm的绿色光谱范围内，其出光功率也可以提高一倍左右。本论文的最后一部分探讨了LED效率下降的可能原因之一。随着驱动电流的增加。提醒本论文的读者，其应有的光荣职责是不要干扰此类作品的优先权。在各种测量中，在低温下在CL中的蓝宝石上的c平面体GaN和MQW上发现了255--260 nm的发光峰。低温EL光谱在267 nm附近也显示出类似的峰。峰值的强度随LED驱动电流而增加。该峰可能来自辐射俄歇复合过程。它可能源自涉及导带更高状态的更高阶跃迁，可能通过俄歇效应填充。

著录项

  • 作者

    Xia, Yong.;

  • 作者单位

    Rensselaer Polytechnic Institute.;

  • 授予单位 Rensselaer Polytechnic Institute.;
  • 学科 Physics Optics.;Energy.;Engineering Materials Science.
  • 学位 Ph.D.
  • 年度 2009
  • 页码 116 p.
  • 总页数 116
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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