High Efficiency Nanostructured Light Emitting Diodes on Nonpolar Substrates

这项研究的目的是提高GaN基发光二极管(LED)的量子效率，使其用于固态照明接近100%。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。这项拟议的研究解决了提高智商(LED)的四个关键科学问题。这些关键的推力包括：(1)在非极性(r-平面)蓝宝石上跨越失配尺度的薄膜外延；(2)通过控制缺陷和界面来管理应力和电荷；(3)纳米结构的厚度变化或有源载流子的量子限制；以及(4)形成低阻透明欧姆接触。蓝宝石衬底上的GaN层具有1.19~16.08%的平面失配，因此，外延层将采用整倍数平面在薄膜-衬底界面上匹配的结构域匹配外延生长。失配应变可以在两个单分子层内松弛，失配位错可以限制在这一层内，以减少穿线位错的密度。利用新型的掺Ga、Al的氧化锌与NiO或MoOx中间层来增加功函数来降低肖特基势垒，可以实现低阻接触。与现有的白炽灯相比，固态照明(SSL)提供了一种全新的照明模式，因此该项目具有巨大的社会效益。与白炽灯的约17 lm/W和荧光灯的约50 lm/W相比，SSL的效率可接近400 lm/W，其功耗比白炽灯低一个数量级，预期寿命超过40年。拟议的研究在研究生的教学和培训方面具有很强的教育成分。

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.