New techniques for large scale growth of ZnO on sapphire substrates

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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.