Epitaxial Light Extraction Structures for Arbitrary GaN Orientations
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Solution Overview
Problem
Current methods for improving light extraction and directionality in III-nitride semiconductor devices, such as LEDs, are limited by their dependence on specific crystal orientations and require delicate fabrication techniques, which are not effective for arbitrary GaN crystal orientations and nonpolar surfaces, and lack control over light emission directionality.
Innovation Solution
A method involving the growth of island-like III-nitride semiconductor layers on a substrate using a growth restrict mask, where the mask is patterned with rough surfaces or photonic crystals, allowing for light guiding or extracting features on the wings of epitaxial lateral overgrowth layers, enabling better crystal quality and independent control of light extraction and directionality without chemical etching or plasma damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If surface roughening methods such as patterned sapphire substrate or photoelectrochemical etching are used, then light extraction efficiency is improved, but the method is limited to specific crystal orientations and not applicable to arbitrary GaN crystal orientations and nonpolar surfaces
Solution Approach 1:
The substrate surface is divided into multiple regions with different crystal orientations using a growth restrict mask, allowing different areas to exhibit different light extraction characteristics. This segmentation enables the device to achieve effective light extraction across various crystal orientations by combining multiple oriented regions.
2Shape
If conventional pattern transfer methods are used, then light guiding features can be created, but chemical etching or plasma damage occurs which degrades crystal quality
Solution Approach 1:
Chemical etching and plasma processes are replaced with a mechanical-free epitaxial growth approach. The light guiding features are formed through controlled epitaxial lateral overgrowth where the crystal structure naturally follows the mask pattern, eliminating chemical or plasma-induced damage to the crystal lattice.
Solution Approach 2:
The growth restrict mask is prepared in advance with the desired pattern before initiating epitaxial growth. This preliminary patterning allows the crystal to self-organize during growth, forming light guiding features without requiring subsequent etching or plasma processing that would compromise crystal quality.
3Ease of operation
If light extraction features are added to improve directionality, then light control is enhanced, but the fabrication process becomes more complex and delicate
Solution Approach 1:
The light extraction efficiency improvement and light directionality control are merged into a single epitaxial growth process. By incorporating the growth restrict mask with integrated patterns during the initial growth stage, both functions are achieved simultaneously without requiring separate fabrication steps, thereby reducing overall process complexity.
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
This approach enhances light extraction and directionality, improves crystal quality, and allows for scalable manufacturing of high-yield, smaller footprint devices that can be fabricated on various substrates, including foreign substrates like Si and sapphire, independent of crystal orientations, and enables recycling of substrates.
Implementation Method 1
growth of island-like III-nitride semiconductor layers on a substrate using a growth restrict mask
Implementation Method 2
the mask is patterned with rough surfaces or photonic crystals, allowing for light guiding or extracting features
Data Source
AI summary
Light emitting devices having light extraction or guiding structures integrated in their epitaxial layers, wherein the light extraction and guiding structures are fabricated using a lateral epitaxial growth technique that transfers a pattern from a growth restrict mask and/or host substrate to the epitaxial layers.