Transparent Window Electrode for Lateral LED Light Extraction
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Solution Overview
Problem
Lateral light emitting diodes face reduced light extraction efficiency due to the opaque nature of traditional n-electrodes and the confinement of light in non-emission regions, leading to current crowding and inefficient light emission.
Innovation Solution
Incorporating a transparent window layer made of low-refractive-index single-crystal oxide in the n-electrode structure to create a light emitting window, along with a non-uniform via hole contact for current spreading, which enhances light extraction and reduces current crowding.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a traditional opaque n-electrode (Ti/Al or Cr/Al) is used, then electrical connection is achieved, but light extraction efficiency is reduced due to light confinement in the MESA region
Solution Approach 1:
The n-electrode material is changed from opaque (Ti/Al or Cr/Al) to transparent (indium tin oxide, ITO), allowing light to pass through the electrode and be extracted from the MESA region, thereby resolving the light confinement problem while maintaining electrical connection functionality
Solution Approach 2:
A composite structure is formed by combining the transparent conductive oxide layer (ITO) with the underlying metal electrode layers (Ti/Al or Cr/Al), creating a multi-layer electrode that provides both electrical conductivity and optical transparency for improved light extraction
2Reliability
If uniform via hole contact is formed, then manufacturing is simplified, but current crowding occurs due to substrate characteristics
Solution Approach 1:
The via hole contact structure is designed with non-uniform characteristics, where the contact holes are strategically positioned and sized to compensate for current crowding effects caused by substrate properties, creating locally optimized current distribution while maintaining overall device functionality
3Shape
If MESA structure is formed by anisotropic plasma etching, then device structure is defined, but light is confined and not extracted in the MESA region
Solution Approach 1:
The MESA region electrode material is changed from opaque to transparent (ITO), enabling light that would otherwise be confined in the MESA structure to pass through the electrode and be extracted, converting the previously light-trapping region into a light-emitting window
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 solution significantly improves light extraction efficiency by allowing trapped light to be emitted through the transparent window layer and uniformly distributes current, thereby increasing the overall efficiency of the light emitting diode.
Implementation Method 1
A critical angle is reduced due to a great difference between gallium nitride (refractive index=2.4) and air (refractive index=1). Thus, the light cannot be emitted to the outside and is totally reflected at the boundary to be confined therein.
Implementation Method 2
A critical angle is reduced due to a great difference between gallium nitride (refractive index=2.4) and air (refractive index=1). Thus, the light cannot be emitted to the outside and is totally reflected at the boundary to be confined therein.
Implementation Method 3
In order to achieve the feature, a light which is not emitted through a non-emission region and is confined in a device is extracted by introducing an electrode having a light emitting window.
Data Source
AI summary
A lateral light emitting diode device includes: a substrate; an n-type GaN layer disposed on the substrate; an activation layer disposed on the n-type GaN layer; a p-type GaN layer disposed on the activation layer; a current spreading layer disposed on the p-type GaN layer; a p-electrode disposed on the current spreading layer; a MESA region formed by removing portions of the current spreading layer, the p-type GaN layer, the activation layer, and the n-type GaN layer; a transparent window layer disposed on the n-type GaN layer in the entire or part of the MESA region; a plurality of contact plugs which is in contact with the n-type GaN layer through the transparent window layer; and an n-electrode disposed on the transparent window layer to connect the plurality of contact plugs to each other.