Abstract
Sapphire Substrate Processing for High-Performance GaN-Based Light-Emitting Diodes -Micropatterning of Sapphire Substrates and Its Effect on Light Enhancement in GaN-Based Light-Emitting Diodes-
Highlights
GaN-based light-emitting diodes (LEDs) have attracted much attention as a key technology for energy-saving devices.[1]
The large mismatch in both the lattice constant and thermal expansion coefficient between GaN and sapphire, which is commonly used as a substrate for GaN epitaxial growth, is the main cause of the former problem.[5]. For the latter one, a narrow escape cone of light, which is around 24.7°, has been pointed out, as there is a large gap in refractive index between GaN and air.[6]. Namely, the current issues are summarized as low internal quantum efficiency (IQE) and low light extraction efficiency (LEE)
As the growth of GaN films starts on the planar surface between bumps, and the grown films coalesce over bumps by epitaxial lateral overgrowth (ELOG), threading dislocation densities (TDDs) are reduced by bending and mutual annihilation of dislocations, which contribute to the IQE improvement
Summary
GaN-based light-emitting diodes (LEDs) have attracted much attention as a key technology for energy-saving devices.[1]. There are mainly two reasons for the insufficient performance of GaN-based LEDs: high dislocation densities in the LED films and low light extraction efficiency. The PSS has a strong effect on LEE improvement, since the patterned surface enhances the light reflections as compared with the planar surface. This increases the probability of light entering into the narrow escape cone, resulting in an increment in the amount in extracted light from LEDs
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