Vertical GaN LED Light Extraction via Rough Pattern
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Solution Overview
Problem
Conventional vertical group III-nitride light emitting devices face low external light extraction efficiency due to total internal reflection, leading to increased heat release and reduced device lifetime, and the manufacturing process is complex, resulting in a small contact area for the n-electrode and increased operating voltage.
Innovation Solution
A vertical group III-nitride light emitting device with a conductive substrate, p-type clad layer, active layer, and an undoped GaN layer having a rough pattern on its top surface, except where the n-electrode is formed, along with a reflective layer and a transparent electrode, to enhance light extraction and reduce operating voltage, and a manufacturing method involving a basic substrate with a pre-formed rough pattern that is transferred to the undoped GaN layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a rough pattern is formed on the n-doped AlGaN contact layer to improve light extraction efficiency, then light extraction efficiency is improved, but the contact area of the n-electrode becomes small and operating voltage increases
Solution Approach 1:
The patent applies local quality by creating different surface characteristics in different regions: the rough pattern is formed only in the light extraction region while the electrode contact region maintains a smooth surface. This allows the rough pattern to scatter light effectively in the light extraction area while providing adequate contact area in the electrode region, thus resolving the contradiction between light extraction efficiency and operating voltage.
2Loss of energy
If a rough pattern is formed on the contact layer to enhance light extraction, then light extraction efficiency is improved, but the manufacturing process becomes complex and yield decreases
Solution Approach 1:
The patent segments the contact layer into two functional regions: a light extraction region with a rough pattern and an electrode contact region with a smooth surface. This segmentation is achieved by forming the rough pattern on a sacrificial layer that is subsequently removed, allowing the pattern to be transferred only to the desired region. This approach simplifies manufacturing by using a straightforward photolithography and etching process rather than requiring complex selective patterning techniques.
3Loss of energy
If the sapphire substrate is removed after attaching the metal substrate to achieve high extraction efficiency, then light extraction efficiency is improved, but it becomes very difficult to perform photolithography on the thin-filmed structure
Solution Approach 1:
The patent applies preliminary action by forming the rough pattern on the sacrificial layer before removing the sapphire substrate. This allows the photolithography and etching processes to be performed when the structure is still supported by the rigid sapphire substrate, making the process feasible. After the rough pattern is formed, the sapphire substrate is removed, leaving the desired pattern on the thin-filmed structure without requiring subsequent difficult photolithography operations.
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 and reduces operating voltage by scattering photons and preventing current concentration, while simplifying the manufacturing process to increase yield and extend device lifetime.
Implementation Method 1
A vertical group III-nitride light emitting device improved in light extraction efficiency... the undoped GaN layer having a rough pattern formed on a top surface thereof... to enable a photon arriving at its surface to scatter randomly
Implementation Method 2
a metal reflective layer 13... stacked on the conductive substrate
Implementation Method 3
The greatest hurdle against light extraction out of the LED is extinction of light resulting from total internal reflection. That is, big refractivity differences at an interface of the LED allows only about 20% of light generated to exit outside the interface of the LED
Data Source
AI summary
A vertical group III-nitride light emitting device and a manufacturing method thereof are provided. The light emitting device comprises: a conductive substrate; a p-type clad layer stacked on the conductive substrate; an active layer stacked on the p-type clad layer; an n-doped AlxGayIn1-x-yN layer stacked on the active layer; an undoped GaN layer stacked on the n-doped layer; and an n-electrode formed on the undoped GaN layer. The undoped GaN layer has a rough pattern formed on a top surface thereof.