LED Light Extraction via Roughened Semiconductor Surface
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Solution Overview
Problem
Light emitting diodes (LEDs) suffer from low luminous efficiency due to high refractive index semiconductor materials causing total reflection and absorption of short wavelength light, such as UVC, resulting in a low light extraction rate.
Innovation Solution
A light emitting diode structure comprising a first semiconductor layer, an active layer, a patterned electrode layer with a roughened surface, a planarization layer, and a reflective layer, where the patterned electrode layer is made of light-transmitting conductive oxide, and the reflective layer is made of metallic material, enhancing light reflection and extraction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional LED structure with smooth surfaces is used, then the device complexity is low and manufacturing is easy, but the light extraction rate is low due to total reflection at the semiconductor-air interface
Solution Approach 1:
The patent applies surface roughening to the semiconductor layer, transforming the smooth planar surface into a curved/rough surface topology. This curvature modification increases the light extraction rate by reducing total internal reflection at the semiconductor-air interface, allowing more light to escape while maintaining manufacturing feasibility through standard semiconductor processing techniques.
Solution Approach 2:
The patent modifies the physical parameters of the semiconductor layer surface by controlling the roughness magnitude (quantified by root mean square roughness values). By adjusting the surface roughness parameter within specific ranges, the light extraction rate is enhanced while maintaining compatibility with existing manufacturing processes, thus resolving the contradiction between ease of manufacture and light extraction performance.
2Use of energy by moving object
If the semiconductor material has a high refractive index to achieve desired optical properties, then the light generation efficiency is improved, but total reflection increases causing energy loss
Solution Approach 1:
The roughened surface creates multiple curved interfaces that reduce total internal reflection. This allows high refractive index semiconductor materials to maintain their light generation efficiency while significantly reducing energy loss through reflection, as the curved surface topology enables more light rays to escape at angles that avoid total reflection.
Solution Approach 2:
The patent converts the harmful effect of total reflection into a beneficial outcome by using the rough surface topology to scatter and redirect light paths. What would normally be total reflection and energy loss is transformed into opportunities for light extraction, turning the high refractive index property from a disadvantage into an advantage for light generation while mitigating its harmful reflective effects.
3Loss of energy
If the second surface of the second type semiconductor layer is highly roughened to improve light extraction, then the light extraction rate increases, but the contact resistance with the electrode layer increases
Solution Approach 1:
The patent applies different surface quality characteristics to different regions: the second surface of the semiconductor layer is roughened to enhance light extraction, while the third surface (contact surface) is kept smooth to ensure low contact resistance with the electrode. This local differentiation of surface properties allows simultaneous optimization of both light extraction and electrical contact performance.
Solution Approach 2:
The patent segments the semiconductor layer into distinct functional surfaces with different roughness characteristics. The light-emitting surface is roughened for enhanced extraction, while the electrode contact surface is maintained smooth for low resistance. This segmentation of functional surfaces resolves the contradiction between light extraction rate and contact resistance by assigning different surface quality requirements to different functional regions.
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 structure significantly increases the light extraction rate and reduces contact resistance, improving the overall luminous efficiency of the LED by minimizing total reflection and enhancing the reflective effect.
Implementation Method 1
due to the higher refractive index of the semiconductor material, only a small portion of the light generated by the light emitting diode is radiated to the outside, and most of the energy is absorbed by the electrode or semiconductor material after numerous times of total reflection
Implementation Method 2
the reflective layer contacts the fourth surface of the planarization layer... enhancing light reflection and extraction
Data Source
AI summary
A light emitting diode includes a first type semiconductor layer, an active layer, a second type semiconductor layer, a patterned electrode layer, a flat layer and a reflective layer. The active layer is disposed on the first type semiconductor layer. The second type semiconductor layer is disposed on the active layer. The second type semiconductor layer includes a first surface and a second surface having a first arithmetic mean roughness. The patterned electrode layer is disposed on the second surface of the second type semiconductor layer. The planarization layer is disposed on the second type semiconductor layer. The planarization layer includes a third surface and a fourth surface. The third surface is in contact with the second surface of the second type semiconductor layer. The fourth surface has a second arithmetic mean roughness that is less than the first arithmetic mean roughness.