| dc.description.abstract | This thesis shows that Pt thin film on (0001) GaN and (0001) sapphire substrates will have self-assemble phenomenon. By dewetting behavior of Pt thin film on hexagonal substrate, we tend to believe that Pt atoms are polarizing by the surface polarization field of the substrate. So, Pt atoms would be affected by the attraction and the repulsion of the internal atoms in the substrate. Then, Pt atom has different stability depending on the locations of the Pt atoms on the different surface sites of the substrate. It causes the Pt film forming the hexagonal mesh formation, which is related to the regular arrangement of Pt atoms on the GaN and sapphire surface. By observing the shape and the angle of Pt meshes, we think that the dewetting of the Pt atoms surface atoms is associated with the different locations on (0001) GaN and (0001) sapphire substrate. From experimental results, Pt meshes are meta-stable state on the GaN and the sapphire substrate. Eventually, Pt thin film transforms to islands.
We note that all meshes not only exist with symmetrical hexagons, but also, exist with asymmetrical hexagons. From the experimental results, we infer three types of mesh growth mechanisms, and three types of meshes growth mechanism could explain that the Pt area between the meshes is the key factor causing symmetrical hexagonal meshes transforming to asymmetrical hexagonal meshes.
Then, by using the nano-scale hexagonal meshes on the (0001) sapphire as hard-mask and high temperature sulfuric acid solution, nano-scale hexagonal cavities could be created on the (0001) sapphire. In this work, we use the nano-cavities hexagonal pattern sapphire substrate as the patterned sapphire wafer to fabricate. GaN-base blue light-emitting diodes. We found that the GaN film grown on the nano-cavities hexagonal patterned sapphire substrate has less threading dislocation than the GaN film grown on the regular pattern sapphire and flat sapphire substrate. Because of the lower defects in the GaN film grown on the nano-cavities hexagonal pattern sapphire substrate, the heat generated by the non-radiative combination is lower than the GaN film grown on flat sapphire substrates. Therefore, the quantum efficiency of the GaN LED on the nano-cavity PSS substrate is better than GaN LED on the regular PSS. | en_US |