High Efficiency Nanostructured Light Emitting Diodes on Nonpolar Substrates

本研究的目的是提高GaN基发光二极管（LED）的量子效率（IQE），使其用于固态照明接近100%。该方法是减少器件层中的有害缺陷，增强光子产生，并创建更好的欧姆接触以增强光子提取。拟议的研究解决了提高IQE（LED）的四个关键科学问题。这些关键的推动力包括：（1）在非极性（r-平面）蓝宝石上的失配尺度上的薄膜外延;（2）通过控制缺陷和界面来管理应力和电荷;（3）有源载流子的纳米结构厚度变化或量子限制，以及（4）形成低电阻率透明欧姆接触。蓝宝石上的GaN层具有范围从1.19至16.08%的平面失配，因此，外延层将通过畴匹配外延生长，其中整数倍的平面在膜-衬底界面上匹配。失配应变可以在两个单层内弛豫，并且失配位错被限制在该层内以降低穿透位错的密度。低电阻率接触将使用新的Ga和Al掺杂的ZnO与NiO或MoOx中间层，这增加了功函数，以减少肖特基势垒。该项目具有巨大的社会效益，因为与现有的白炽灯照明相比，固态照明（SSL）提供了一种全新的照明模式。SSL效率可以接近400 lm/W，相比之下，白炽灯泡的效率约为17 lm/W，荧光灯泡的效率约为50 lm/W，SSL中的功耗比白炽灯照明低一个数量级，预期寿命超过四十年。拟议的研究有很强的教育成分，在教学和研究生的培训。

The objective of this research is to enhance the quantum efficiencies (IQE) of GaN based light emitting diodes (LEDs) to be used for solid state lighting closer to 100%. The approach is to reduce harmful defects in device layers and enhance photon generation and create better Ohmic contacts to enhance photon extraction. The proposed research addresses four critical scientific issues in enhancing IQE (LEDs). These critical thrusts include: (1) thin film epitaxy across the misfit scale on nonpolar (r-plane) sapphire; (2) management of stresses and charge through control of defects and interfaces; (3) nanostructured thickness variation or quantum confinement of active carriers, and (4) formation of low-resistivity transparent Ohmic contacts. The GaN layers on sapphire have planar misfit ranging from 1.19 to 16.08%, therefore, epitaxial layers will be grown by domain matching epitaxy where integral multiples of planes match across the film-substrate interface. The misfit strain can be relaxed within two monolayers and the misfit dislocations confined within this layer to reduce the density of threading dislocations. Low-resistivity contacts will be created using novel Ga- and Al-doped ZnO with NiO or MoOx interlayer which increases the work function to reduce Schottky barrier. There is a tremendous societal benefit from this project as the solid-state lighting (SSL) offers an entirely new lighting paradigm, compared to existing incandescent lighting. The SSL efficiency can approach 400 lm/W, compared to ~ 17 lm/W for incandescent bulb and ~ 50 lm/W for fluorescent bulb with power consumption in SSL an order of magnitude lower than incandescent lighting and life expectancy of over forty years. The proposed research has a strong educational component in terms of teaching and training of graduate students.