Analyzed by MOCVD GaN-Based Optoelectronic Devices Grown on Sapphire Substrates

Using MOCVD (metal-organic chemical vapor deposition) to analyze the growth of GaN-base photoelectric devices on the sapphire substrate is a common method in the semiconductor lighting industry. In recent years, along with the unceasing enhancement of epitaxy technology and related technologies, larger sapphire substrates are needed. The optimization and improvement of MOCVD reaction chamber structure with large-scale epitaxial wafers have been studied by many domestic researchers. Li et al. optimized high-frequency heating graphite base groove structure with eight-inch and twelve-inch substrates. Ying-lu et al.studied the heating modulate curve of radiation heating MOCVD and proposed the design principles of the outer heater. To improve the production efficiency, some great MOCVD manufacturers also focus on how to improve and increase the MOCVD cavity and the sapphire substrate size in foreign countries. At present, two-inch and four-inch epitaxial wafers are frequently used, so manufacturers who can produce six-inch SiC and Si substrate epitaxial wafers with high quality in foreign countries would sell chips abroad.

With the growth of the III-nitrides, sapphire becomes the most extensively used substrate material. Crystals of sapphire with good quality and low price can be easily got. Besides, sapphire is stable at high temperature and the growth technology of nitrides on sapphire is now fairly mature. However, the problem of wafer bowing, which results from the difference in thermal expansion coefficient between GaN epitaxial layer and sapphire, has become much more serious in larger-diameter wafers. It will deteriorate the contact between the substrates and the equipment stages or the subsectors during device process, which will result in degradation in the device uniformity or failures in lithography.

By using finite element simulation software, the relationship between the maximum wafer bowing and sapphire substrate size under characteristic temperature is studied in the case of the growth of GaN in the sapphire substrate, and the wafer bowing relation equation is also deduced. The research work in this paper plays a foreshadowing role for later research sapphire epitaxial growth and MOCVD reaction chamber structure improvement.


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