| dc.description.abstract | In this thesis, the etching mechanism of the c-plane sapphire substrate will be investigated. In the past, we think that the wet-etching morphology depends on etching resistance of the sapphire crystallography (a-plane > r-plane > c-plane). In this study, we found that the wet-etching morphology of the c-plane sapphire would not follow the etching resistance of the sapphire crystallography. In Chapter 3, the wet-etching mechanism and the formation of the etching morphology is investigated by establishing the sapphire atomic model and the calculation of the surface energy in each crystal plane. So, we conclude that the etched c-plane sapphire will not take crystal r-plane as the pattern side-facets, when the oxygen atom on the r-plane is not protected by a hard mask during the etching process.
The wet-etching process is one of the chemical reactions, so, the mixture of the chemical etching solution would affect the wet-etching morphology. In Chapter 4, different ratio of the sulfuric acid and the phosphoric acid in the etching solution will affect the bottom of the wet-etching pattern. The shape of the wet-etching pattern bottom would be formed by straight lines as increasing the amount of the phosphoric acid in the etching solution. With establishing the atomic model, we realize that the function of the acid etchants, and the location of the etching sites in different dimensions. We propose a so-called spatial screen effect of the etchant, which will reduce the etching rate in the etching process. The spatial screen effect of the etchants will result in the different etching rate in two-dimension etching morphology and then affect the wet-etching morphology. After realizing the etching mechanism and the effect of the etching solution on the etching morphology, the patterned sapphire substrate is applied to fabricate the LED chips. Patterned sapphire substrate can effectively improve LED efficiency, and we also find that the pattern morphology will affect the spatial intensity distribution of the blue GaN-LED. In Chapter 5, the blue GaN-LED grown on different patterned sapphire substrates will be processed with the white-light LED package and the wet-etching pattern morphology effect on the white-light LED package efficiency was investigated. The energy loss in the white-light LED package process is unavoidable. Therefore, in this study, we have proved that by adjusting the spatial intensity distribution of the GaN-LED, the energy loss can be reduced and then white-light LED package efficiency can be improved. However, by controlling the dihedral angle of the pattern side-facets, the spatial intensity distribution of the GaN-LED is adjustable. The above concept is built on the basis of the sapphire wet-etching mechanism and the etching solution effect on the etching morphology.
In this thesis, the etching mechanism of the mask-free patterned sapphire substrate and the steric effect of anion on the wet-etching patterned sapphire morphology are presented. Besides, the PSS effect on the white-light LED package efficiency is established to further enhance the white-light LED efficiency.
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