GaN LED Surface Roughening for Light Extraction
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Solution Overview
Problem
Conventional light emitting diodes (LEDs) suffer from low efficiency due to total internal reflection (TIR) of light within the semiconductor chip, which limits the emission of generated light, and existing methods to enhance light extraction, such as surface texturing and periodic patterning, face challenges like manufacturing difficulties and interference with current spreading layers.
Innovation Solution
A photo-electrochemical oxidation and etching process is used to roughen the surface of the n-GaN layer in LEDs, creating a non-ordered textured morphology that enhances light extraction by optimizing the surface roughness and refractive index matching, allowing more light to escape without compromising current spreading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If surface texturing is applied to reduce total internal reflection, then light extraction efficiency is improved, but current spreading is hindered
Solution Approach 1:
The patent divides the LED structure into distinct functional zones: a textured light-emitting surface for optimal light extraction and a separate current spreading layer with different morphology for electrical conduction. This segmentation allows each layer to be optimized independently for its specific function without compromise.
Solution Approach 2:
The patent applies different surface qualities to different regions: the light-emitting surface has a specific roughness (RMS 0.03-0.3 micrometers) optimized for light extraction, while the current spreading layer maintains different properties optimized for electrical conduction. This local quality differentiation resolves the contradiction between light extraction and current spreading.
2Loss of energy
If periodic patterning is used to redirect light, then light extraction is enhanced, but manufacturing complexity increases
Solution Approach 1:
The patent extracts the light redirection function from the surface pattern itself and transfers it to strategically positioned reflective elements and internal interfaces. This removes the need for complex periodic surface patterning while maintaining light extraction enhancement.
Solution Approach 2:
The patent introduces reflective elements and internal interfaces as intermediary structures that perform the light redirection function. These intermediaries simplify the surface geometry while achieving the same optical effect, reducing manufacturing complexity.
3Ease of operation
If a current spreading layer is deposited on a textured surface, then current distribution is improved, but light transmission through the layer is reduced
Solution Approach 1:
The patent segments the device into distinct functional layers: a textured surface layer for light extraction and a separate current spreading layer for electrical conduction. This segmentation allows the current spreading layer to be optimized for electrical function without compromising light transmission, as the light extraction function is already fulfilled by the textured surface.
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 method significantly increases the luminance of LEDs by more than two times compared to those with flat surfaces, enabling more efficient light extraction and potentially reducing chip size and power consumption while maintaining cost competitiveness.
Implementation Method 1
A photo-electrochemical oxidation and etching process is used to roughen the surface of the n-GaN layer in LEDs
Implementation Method 2
A photo-electrochemical oxidation and etching process is used to roughen the surface of the n-GaN layer in LEDs
Implementation Method 3
The textured surface has features on the order of the wavelength of light that refract and reflect light in a manner not predicted by Snell's law due to random interference effects
Implementation Method 4
Light that reaches the surface beyond the critical angle will not cross but will experience total internal reflection (TIR)
Implementation Method 5
The textured surface has features on the order of the wavelength of light that refract and reflect light in a manner not predicted by Snell's law due to random interference effects
Data Source
AI summary
Systems and methods are disclosed for fabricating a semiconductor light-emitting diode (LED) device by forming an n-doped gallium nitride (n-GaN) layer on the LED device and roughening the surface of the n-GaN layer to extract light from an interior of the LED device.