Research on GaN Light Emitting Devices on Quasi-Single Crystal Metal Substrates

本项目的目的是开发一种在准单晶金属基板上生长高质量GaN晶体的技术，并证明该技术在低功耗大面积显示器，移动纸张显示器和高效照明方面应用的可行性。的确，氮化镓及其相关晶体已被认为是全彩大面积显示的有前途的材料，但这些材料存在成本高、面积小等严重问题。最近，我们发现在良好控制的条件下，金属衬底的晶粒尺寸可以达到几米，并且高质量的GaN和相关化合物如AlN和InGaN在金属衬底上生长。由于晶粒尺寸远大于载流子扩散长度，我们可以期望使用金属基板以低成本制造高效率的大面积光显示器。为了在金属衬底上成功地实现半导体外延生长，金属表面的清洗工艺和高质量缓冲层的形成是至关重要的。我们发现，在抛光过程中精确控制pH值，并在缓冲层生长之前使用In等离子体，可以实现原子平面金属表面。我们还发现，使用射频等离子体自由基源可以改善缓冲层的薄膜质量。利用这些技术，我们已经成功地在金属准单晶金属衬底上生长出具有强近带边缘发射的高质量GaN晶体。

The purpose of this project is to develop a growth technique of high quality GaN crystals on the quasi-single crystal metal substrates and to demonstrate the feasibility of this technique for the application of the low power large area displays, mobile paper displays, and high efficiency lighting. It is true GaN and its related crystals have been regarded as promising materials for full color large area displays, but these materials suffer from several serious problems which include its high cost and small area. Recently, we have found that the grain size of metal substrates can be reached to several meters with annealing under well-controlled conditions and that high quality GaN and related compounds such as AlN and InGaN grow on the metal substrates. Since the grain size is much larger than the carrier diffusion length, we can expect fabrication of high efficiency large area light displays at low cost with the use of the metal substrates. For the successful epitaxial growth of semiconductors on metal substrates, cleaning process of the metal surfaces and formation of high quality buffer layers are inherently important. We have found that atomically flat metal surfaces can be achieved with the precise control of pH values during polishing and with the use of In plasma just before the growth of the buffer layers. We have also found that film quality of the buffer layer can be improved with the use of radio frequency plasma radical source. With these techniques, we have succeeded in growing high quality GaN crystals with strong near band edge emission on metal quasi-single crystal metal substrates.