Vertical GaN LED with TCO Layer for Light Escape
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Solution Overview
Problem
GaN-based light emitting devices with vertical structures face challenges in heat dissipation and manufacturing complexity due to the use of sapphire substrates, which limit light escape efficiency and increase production costs.
Innovation Solution
The implementation of a transparent conductive oxide (TCO) layer, such as ZnO, over a GaN semiconductor layer, combined with a getter metal for ohmic contact, enhances light emission and escape efficiency by reducing contact area resistance and increasing the light escape angle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a sapphire substrate is used for GaN-based LED fabrication, then the LED can be manufactured with good thermal stability and high-temperature processability, but the light escape efficiency is limited due to the insulating nature of sapphire
Solution Approach 1:
The patent removes the sapphire substrate from the final LED structure through laser lift-off technology. The sapphire substrate is used only temporarily during the growth phase to provide thermal stability and high-temperature processability, then extracted before the product is completed to eliminate its insulating barrier effect on light escape.
Solution Approach 2:
The patent separates the manufacturing process into distinct phases: growth phase (using sapphire substrate for stability) and operation phase (without sapphire substrate for light escape). This segmentation allows each phase to benefit from the most appropriate substrate configuration.
2Temperature
If a vertical structure is adopted for GaN-based LEDs, then the heat dissipation is improved, but the manufacturing complexity increases due to substrate removal requirements
Solution Approach 1:
The patent introduces laser lift-off technology as an intermediary process that simplifies the substrate removal step. The laser provides a clean, precise, and controllable method to separate the GaN layer from the sapphire substrate, reducing manufacturing complexity compared to mechanical or chemical removal methods.
3Area of stationary object
If the contact area between electrode and semiconductor layer is reduced, then the light emission area is increased, but the contact area resistance increases
Solution Approach 1:
The patent changes the electrical parameters of the contact interface by introducing a getter metal layer that forms an ohmic contact with the n-type GaN layer. This allows the contact area to be minimized for light emission while maintaining low resistance through improved contact quality rather than increased area.
Solution Approach 2:
The patent uses a composite contact structure consisting of a transparent conductive oxide layer and a getter metal layer. This composite structure provides both electrical conductivity and optical transparency, enabling small contact areas to achieve both low resistance and high light emission efficiency.
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
This configuration improves light emission efficiency, reduces operating voltage, and significantly increases the light escape angle from 25° to 61.74°, addressing the limitations of traditional GaN-based LED structures.
Implementation Method 1
increasing the light escape angle
Implementation Method 2
getter metal for ohmic contact, enhances light emission and escape efficiency by reducing contact area resistance
Data Source
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AI summary
A light emitting device having a vertical structure, which is capable of achieving an enhancement in light escape efficiency includes a semiconductor layer having a first surface and a second surface, a first electrode arranged on the first surface of the semiconductor layer, a transparent conductive oxide (TCO) layer arranged on the second surface of the semiconductor layer, and a second electrode arranged on the TCO layer. Methods of manufacture are also disclosed.