LED Nanostructured Surface Enhances Light Extraction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The efficiency of light emitting diodes (LEDs) is limited by total internal reflection (TIR), which causes light to be reflected back into the device and lost due to absorption, especially when the difference in refractive indices between the LED materials and the environment is significant, leading to nonuniform current distribution and reduced light extraction.
Innovation Solution
A nanostructured surface with a quasi-periodic, anisotropic array of elongated ridge elements having a wave-ordered structure pattern is created on the LED surface, formed using a wavelike nanomask made from aluminum-containing semiconductor materials, to enhance light extraction by scattering light and improving the quality of epitaxial semiconductor layers.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a roughened surface is formed by PEC oxidation and etching to enhance light extraction, then light extraction efficiency is improved, but current distribution becomes nonuniform due to thickness nonuniformity in the n-type layer
Solution Approach 1:
The patent changes the surface morphology parameters by creating controlled nanostructures (ridges, gratings, or holes) with specific geometries rather than random roughness. The surface is structured with defined period, depth, and width parameters that can be precisely controlled during fabrication, transforming the uncontrolled PEC etching process into a precision nanostructuring process that maintains layer thickness uniformity while enhancing light extraction.
Solution Approach 2:
The patent applies local quality by creating specific nanostructure patterns (ridges, gratings, or holes) at the light-emitting surface with controlled spatial distribution. These localized structural modifications are designed to enhance light extraction in specific regions without affecting the overall uniformity of the semiconductor layer thickness, thereby resolving the contradiction between light extraction enhancement and current distribution uniformity.
2Loss of energy
If micron- and submicron-sized roughness with random profile is created to enhance light extraction, then light extraction is improved, but consistency is lost which is not compatible with thinning LED layers to less than 3 μm
Solution Approach 1:
The patent transforms the random surface roughness into controlled nanostructures with precisely defined parameters including period (20-200 nm), depth (50-500 nm), and width (10-100 nm). These parameter-controlled structures provide both enhanced light extraction and manufacturing consistency, enabling their application in thin-film LEDs with total thickness less than 3 μm.
Solution Approach 2:
The patent transitions from two-dimensional random surface roughness to three-dimensional ordered nanostructures with controlled geometry in multiple dimensions. The nanostructures feature specific height, width, and periodic spacing, creating a structured surface topology that simultaneously achieves light extraction enhancement and structural consistency required for thin-film LED fabrication.
3Illumination intensity
If the growth substrate is removed to improve optical characteristics and reduce resistance, then optical performance is improved, but the surface becomes more susceptible to TIR losses
Solution Approach 1:
The patent applies preliminary action by forming the nanostructured surface on the light-emitting layer before final device assembly. The nanostructures (ridges, gratings, or holes) are created in advance on the exposed n-type layer surface after substrate removal, preparing the surface to minimize TIR losses before the LED is packaged and operated.
Solution Approach 2:
The patent changes the surface parameters by introducing nanostructures with controlled geometry (period 20-200 nm, depth 50-500 nm) on the light-emitting surface. These parameter-controlled modifications reduce TIR losses by scattering and redirecting light that would otherwise be reflected back into the LED, thereby recovering energy that would be lost after substrate removal.
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 nanostructured surface increases light output and improves the quality of epitaxial semiconductor layers, leading to enhanced light extraction and increased efficiency of LEDs by reducing TIR losses and ensuring consistent current distribution.
Implementation Method 1
irradiating a surface of the amorphous silicon with an oblique beam of nitrogen ions to form a wave-ordered structure in the layer of amorphous silicon
Implementation Method 2
further irradiating the surface of the amorphous silicon with an oblique beam of nitrogen ions to transfer the wave-ordered structure to a surface of the aluminum-containing semiconductor layer
Implementation Method 3
The nanostructured surface increases light output and improves the quality of epitaxial semiconductor layers, leading to enhanced light extraction and increased efficiency of LEDs by reducing TIR losses
Implementation Method 4
Light emitting diodes (LEDs) have an active layer of semiconductor material sandwiched between n-type and p-type semiconductor doped layers. When a voltage is applied between the doped layers, an electric current is passed through the LED. Charge carriers, electrons from n-layer or holes from p-layer, are injected into the active layer where they recombine to generate light.
Data Source
Figure 1A~1B
Figure 1C~1D
Figure 1E
AI summary
A light emitting diode has a plurality of layers including at least two semiconductor layers. A first layer of the plurality of layers has a nanostructured surface which includes a quasi-periodic, anisotropic array of elongated ridge elements having a wave-ordered structure pattern, each ridge element having a wavelike cross-section and oriented substantially in a first direction.