| Summary: | 碩士 === 國立交通大學 === 材料科學與工程學系所 === 108 === Light emitting diodes (LEDs) have gradually replaced incandescent-filament lamp in the recent years due to their advantage of small size, long life span and high luminous efficiency, which it is commonly used in street lamps, car headlights, screen backlight source, and traffic signs. Currently, the most commonly used material for LEDs is gallium nitride (GaN). However, since GaN lacks its own substrate, most of the sapphire substrate is used to epitaxy GaN, but there are still some problems between the sapphire and GaN such as lattice mismatch and thermal expansion coefficient difference, therefore, causes defects occurs which leads to the decrease of internal quantum efficiency (IQE). Hence, our common method is to use pattern sapphire substrates (PSS) which bends the dislocation and increase the surface roughness to change the light path, thus can improve the internal quantum efficiency (IQE) and light extraction rate (LEE).
To study the epitaxial quality of patterned aluminum nitride buffer layer on a flat sapphire substrate, in this experiment, a concave and convex patterned AlN buffer on flat sapphire substrate was fabricated, followed up with epitaxial
III
GaN was analyzed. It was found in the experiment that different size of V-pits can be designed by controlling the diameter and spacing of concave AlN buffer layer. In addition to the size difference of concave AlN buffer layer, the small sized V-pits were hexagonal, formed by six inclined crystal planes. The larger sized V-pits were dodecagonal, these V-pits were formed by inclined triangular and rectangular surfaces, thus obtaining specific crystal planes. On the other hand, since the convex AlN buffer layer cannot provide sufficient AlN area for epitaxial growth, GaN will selectively grow on both AlN and sapphire c-plane, resulting chaos GaN growth on convex AlN buffer layer.
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