Vertical UV LED Electrode Layout for Low-Voltage Light Extraction
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Solution Overview
Problem
Current technologies face challenges in achieving a vertical ultraviolet light-emitting diode structure using an n-type conductive AIN substrate with high luminous efficiency and low operating voltage, as existing substrate peeling methods are ineffective for AlGaN-based materials, leading to issues with dislocation and reliability.
Innovation Solution
A vertical ultraviolet light-emitting diode is developed with an AlGaN layer and GaN layer deposited on an n-type AIN single crystal substrate, featuring a specific n-electrode shape and damage layer management, along with a semipolar plane configuration to enhance emission properties and reduce operating voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If a vertical ultraviolet light-emitting diode structure is adopted, then output is improved, but manufacturing difficulty increases due to ineffective substrate peeling methods for AlGaN-based materials
Solution Approach 1:
The patent extracts and removes the sapphire substrate from the AlGaN layer through laser lift-off technique, enabling the formation of a vertical structure with electrodes on both front and rear surfaces. This extraction of the substrate allows the active layers to be transferred to a new substrate or used as standalone vertical LEDs, resolving the manufacturing difficulty by providing an effective substrate removal method for AlGaN-based materials.
Solution Approach 2:
The patent inverts the conventional horizontal electrode configuration by forming electrodes on both the front surface (p-type side) and rear surface (n-type side) of the vertical structure. This inversion of the electrode arrangement enables current injection from both directions, significantly increasing the output while maintaining manufacturability through the laser lift-off process.
2Reliability
If dislocation density is reduced to improve luminous efficiency, then reliability is improved, but substrate requirements become more stringent
Solution Approach 1:
The patent introduces an AlN buffer layer as an intermediary between the sapphire substrate and the AlGaN active layers. This buffer layer acts as a mediator that accommodates lattice mismatch and reduces dislocation density, thereby improving luminous efficiency and reliability without requiring extremely stringent substrate specifications. The buffer layer absorbs the stress and prevents dislocation propagation into the active regions.
Solution Approach 2:
The patent employs a composite structure consisting of multiple layers including sapphire substrate, AlN buffer layer, and AlGaN active layers with different compositions. This composite material approach allows each layer to perform its specific function: the sapphire provides mechanical support, the AlN buffer reduces dislocations, and the AlGaN layers emit light. The composition is modulated to optimize both reliability and substrate compatibility.
3Device complexity
If laser lift-off method is used for substrate peeling, then vertical structure is achieved, but effective peeling is not possible for AlGaN-based materials
Solution Approach 1:
The patent modifies the laser lift-off process parameters specifically for AlGaN-based materials by adjusting laser wavelength, pulse duration, and energy density. These parameter changes enable effective peeling of AlGaN layers from sapphire substrates, overcoming the limitation that conventional laser lift-off parameters work for GaN but not for AlGaN. The optimized parameters allow selective removal of the AlGaN layer while leaving the sapphire substrate intact.
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 enables a vertical ultraviolet light-emitting diode with improved output and reduced operating voltage, achieving efficient light extraction and uniform emission distribution, while minimizing the impact of dislocations and substrate damage.
Implementation Method 1
an ultraviolet light-emitting diode having an emission peak wavelength in range of 210 to 300 nm
Implementation Method 2
an n-electrode formed on a plane on the opposite side to the aluminum polar plane of the n-type AIN single crystal substrate, the n-electrode being provided with at least one opening functioning as a light extraction window
Data Source
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AI summary
Provided is a vertical ultraviolet light-emitting diode having higher luminous efficiency at a lower operating voltage. The vertical ultraviolet light-emitting diode according to the present invention has, on an aluminum polar plane of an n-type AlN single crystal substrate, a layer represented by n-type AlXGa1-XN (wherein X is a rational number satisfying 0.5≤X≤1.0), an active layer, a layer represented by p-type AlYGa1-YN (wherein Y is a rational number satisfying 0.5≤Y≤1.0) and a p-type GaN layer in this order and which is equipped with a p-electrode formed on the p-type GaN layer and an n-electrode partially provided on a plane on the opposite side to the aluminum polar plane of the n-type AlN single crystal substrate, preferably an n-electrode formed by providing at least one opening functioning as a light extraction window, wherein the shortest distance between the n-electrode and an arbitrary point in a portion where the n-electrode is not provided, is not more than 400 µm.