Abstract
We study three different gallium-nitride (GaN) based light emitting diode (LED) cases based on the different locations of the pyramid textures. In case 1, the pyramid texture is located on the sapphire top surface, in case 2, the pyramid texture is locate on the P-GaN top surface, while in case 3, the pyramid texture is located on both the sapphire and P-GaN top surfaces. We study the relationship between the light extraction efficiency (LEE) and angle of slant of the pyramid texture. The optimization of total LEE was highest for case 3 among the three cases. Moreover, the seven escape paths along which most of the escaped photon flux propagated were selected in a simulation of the LEDs. The seven escape paths were used to estimate the slant angle for the optimization of LEE and to precisely analyze the photon escape path.
Highlights
Light emitting diodes (LEDs) have come to be regarded as an important light source in recent years due to their many advantages such as energy saving, high reliability, longer lifetime, environmental protection, faster switching and compact forms
The higher texture density in the GaN-based LED enhances the scattering effect, so the total light extraction efficiency (LEE) is uniform throughout a larger angular region
We study three types of the GaN-based LED based on the different locations of the pyramid textures
Summary
Light emitting diodes (LEDs) have come to be regarded as an important light source in recent years due to their many advantages such as energy saving, high reliability, longer lifetime, environmental protection, faster switching and compact forms. Improving the LEE is important, and various methods such as surface textures [3–5], patterned sapphire substrates [6–8], chip shaping [9], and photonic crystals have been tested as a means to accomplish this. Both wave and geometrical optics have been used to simulation the LEE of the LEDs. In geometrical optics, the rays with a uniform direction can be interrupted by various events, such as scattering, absorption and reemission in the active region, absorption inside the other semiconductor layers, or Fresnel loss of media with different refractive indices. Since the seven escape paths occupy the largest part of the LEE, they dominate the LEE phenomenon in the LED and the paths can be explained by the angular space directly
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