New techniques for large scale growth of ZnO on sapphire substrates

半导体在过去的14年里彻底改变了照明行业。直到1994年，可见光谱中还存在很大的空白。虽然明亮的红色发光二极管（LED）已经存在了几十年，但研究人员还无法实现明亮、可靠的蓝色和绿色器件。日亚化学在1994年展示了长寿命的蓝、绿、白氮化镓led，开创了一个价值数十亿美元的照明产业。然而，挑战依然存在。镓是一种相对昂贵的元素，目前尚不清楚GaN能否满足未来对低成本、高效率照明的需求。紫外发射在某些应用中是理想的，但受到氮化镓铝质量的限制。作为一种替代材料，氧化锌有可能解决几个问题。锌比镓丰富得多，而氧是比氨更安全的氮化镓来源。ZnO的带隙进一步进入蓝色，可能实现紫外线操作。然而，还有巨大的挑战需要克服。目前氧化锌的质量对led来说是不够的。存在严重的缺陷密度问题，p掺杂是led的必要要求，但尚未被证明具有适合led的性能。大多数GaN led现在是由一种称为有机金属气相外延（OMVPE）的晶体生长技术制成的。我们将通过改进的OMVPE技术在由我们的工业合作伙伴Honeywell Electronic Materials of Victoria， BC生产的蓝宝石衬底晶体上研究ZnO的生长。我们将专注于提高该技术在蓝宝石衬底上生长的ZnO的晶体质量和p掺杂，并引入各种先进的表征技术来解决这个问题。霍尼韦尔将与我们一起了解蓝宝石衬底条件对所得外延薄膜的影响。这些信息将用于改进他们的蓝宝石生产工艺。这项工作的最终目标是证明在蓝宝石上生长的ZnO的电学性能有显著改善，从而大大提高对蓝宝石衬底的需求。

Semiconductors have revolutionized the lighting industry over the past 14 years. Until 1994, there was a large void in the visible spectrum. While bright red light emitting diodes (LED) have been around for a few decades, researchers were unable to achieve bright, reliable blue and green devices. The demonstration of long lifetime blue, green, and white gallium nitride LEDs by Nichia Chemical in 1994 opened up a multibillion dollar lighting industry. However, challenges still remain. Gallium is a relatively expensive element and it is not clear that GaN can meet future demand for low cost, high efficiency lighting. Ultraviolet emission is desirable for some applications, but is limited by the quality of aluminum gallium nitride. An alternative material, zinc oxide has the potential to solve several problems. Zinc is much more abundant than gallium, and oxygen is a much safer source than ammonia, the common GaN source. The bandgap of ZnO is further into the blue, possibly enabling ultraviolet operation. However, there are tremendous challenges to overcome. The current quality of zinc oxide is not sufficient for LEDs. There are severe problems with defect density, and p-doping, a necessary requirement for LEDs has not yet been demonstrated with suitable properties for LEDs. Most GaN LEDs are now made by a crystal growth technique called organometallic vapor phase epitaxy (OMVPE). We will investigate the growth of ZnO by a modified OMVPE technique on sapphire substrate crystals produced by our industrial partner, Honeywell Electronic Materials of Victoria, BC. We will focus on improving the crystal quality and p-doping of ZnO grown by this technique on sapphire substrates and bring a variety of advanced characterization techniques to bear on the problem. Honeywell will work with us to understand the effect of sapphire substrate conditions on the resulting epitaxial films. This information will be used to improve their sapphire production process. The ultimate goal of the work is to demonstrate significant improvements to the electrical properties of ZnO grown on sapphire, thereby greatly enhancing the demand for sapphire substrates.