LED Transparent Electrode with Micro-Lenses for Current Spreading
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
GaN-based light emitting diodes face issues with current crowding due to high specific resistance in p-type semiconductor layers, leading to reduced luminous efficiency and light emitting area, and optical losses from total internal reflection, especially in large-scale LEDs.
Innovation Solution
A light emitting diode design featuring a substrate with a transparent electrode layer having concave and convex portions, including micro-lenses on the transparent electrode layer to enhance current spreading and light extraction efficiency, along with strategically placed electrode pads and pad extensions for uniform current distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a transparent electrode layer is formed on the p-type semiconductor layer to enhance current spreading, then current distribution is improved, but optical loss occurs due to total internal reflection caused by refractive index difference
Solution Approach 1:
The patent introduces a convex lens layer on the transparent electrode layer that transforms flat surfaces into curved optical elements. These convex lenses have varying focal lengths that redirect light paths, enabling light to escape the high-refractive-index GaN layer by bending light rays at angles that avoid total internal reflection, thus reducing optical loss while preserving current spreading benefits
Solution Approach 2:
The patent introduces a microlens array as an intermediary optical element between the transparent electrode layer and the external environment. This microlens array acts as a mediator that transforms the optical properties of light passing through the transparent electrode, converting trapped light into extractable light by refraction and focal concentration, thereby reducing optical loss without affecting the electrical current spreading function
2Ease of operation
If pad extensions and multiple electrode pads are formed to assist current spreading, then current distribution is improved, but light emitting area is reduced
Solution Approach 1:
The patent segments the current injection function across multiple p-type electrode pads distributed at different locations on the transparent electrode layer, rather than using a single large pad or extensive pad extensions. This segmentation allows current to be injected at multiple points simultaneously, achieving uniform current spreading across the light emitting area without requiring pad structures that would occupy and reduce the active light emitting region
3Reliability
If the thickness of the transparent electrode layer is increased to improve current spreading, then electrical conductivity is improved, but light absorption increases
Solution Approach 1:
The patent optimizes the thickness parameter of the transparent electrode layer to a specific range that balances electrical and optical requirements. Additionally, the patent changes the optical parameter by introducing the convex lens layer with specific refractive index and focal length characteristics, which compensates for the limited current spreading capability of thin electrode layers while dramatically improving light extraction efficiency, thus allowing use of thinner, less absorptive electrode layers
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves improved luminous efficiency and light extraction efficiency by ensuring uniform current spreading and reducing optical losses, maintaining a large light emitting area without increasing the number of processes or package yield issues.
Implementation Method 1
electric current supplied from the P-electrode pad may be dispersed by the transparent electrode layer before entering the p-type semiconductor layer
Implementation Method 2
optical loss may occur due to total internal reflection caused by a difference in refractive index between the transparent electrode layer and the exterior
Implementation Method 3
optical loss may occur due to total internal reflection caused by a difference in refractive index between the transparent electrode layer and the exterior
Implementation Method 4
a light emitting diode including a substrate, a light emitting structure arranged on the substrate and including a first conductivity-type semiconductor layer, an active layer, and a second conductivity-type semiconductor layer, a transparent electrode layer arranged on the second conductivity-type semiconductor layer and including an upper convex-concave surface having a plurality of concave portions
Data Source
AI summary
Exemplary embodiments of the present invention relate to light emitting diodes. A light emitting diode according to an exemplary embodiment of the present invention includes a substrate having a first side edge and a second side edge, and a light emitting structure arranged on the substrate. The light emitting structure includes a first conductivity-type semiconductor layer, an active layer, and a second conductivity-type semiconductor layer. A transparent electrode layer including a concave portion and a convex portion is arranged on the second conductivity-type semiconductor layer. A first electrode pad contacts an upper surface of the first conductivity-type semiconductor layer and is located near a center of the first side edge. Two second electrode pads are located near opposite distal ends of the second side edge to supply electric current to the second conductivity-type semiconductor layer. A first pad extension extends from the first electrode pad and a second pad extension extends from each of the two second electrode pads.