New techniques for large scale growth of ZnO on sapphire substrates

在过去的14年里，半导体彻底改变了照明行业。直到1994年，在可见光谱中有一个很大的空白。虽然明亮的红色发光二极管（LED）已经存在了几十年，但研究人员无法实现明亮，可靠的蓝色和绿色设备。1994年，日亚化学公司展示了长寿命的蓝色、绿色和白色氮化镓LED，开创了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。紫外线发射对于某些应用是期望的，但是受到氮化铝镓的质量的限制。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，氧是比常见的GaN源氨安全得多的来源。ZnO的带隙进一步进入蓝色，可能使紫外操作。然而，还有巨大的挑战需要克服。目前氧化锌的质量不足以用于LED。存在缺陷密度和p掺杂的严重问题，对于LED的必要要求尚未被证明具有LED的合适性质。现在大多数GaN LED都是通过称为有机金属气相外延（OMVPE）的晶体生长技术制成的。我们将研究通过改进的OMVPE技术在蓝宝石衬底晶体上生长ZnO，该蓝宝石衬底晶体由我们的工业合作伙伴，位于不列颠哥伦比亚省维多利亚的霍尼韦尔电子材料公司生产。我们将专注于提高晶体质量和p型掺杂的ZnO通过这种技术生长在蓝宝石衬底上，并带来了各种先进的表征技术来承担的问题。霍尼韦尔将与我们合作，了解蓝宝石衬底条件对外延薄膜的影响。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.