Semipolar Nitride Layer Growth on Patterned Substrate
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Solution Overview
Problem
Green LEDs based on gallium nitride (GaN) suffer from low efficiency due to crystallographic defects and polarization effects, particularly in the green wavelength region, resulting in a 'green gap' where efficiency is significantly lower than in blue and ultraviolet LEDs.
Innovation Solution
A method involving the creation of semipolar layers by etching parallel grooves and trenches on a substrate to reduce the footprint of nitride materials, allowing epitaxial growth from {111} oriented facets, which minimizes defects and stress, thereby enhancing the efficiency of green LEDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If epitaxial growth is performed on a substrate with conventional c-plane orientation, then growth is relatively easy and device fabrication is simplified, but quantum confined Stark effect and piezoelectric polarization occur causing severe efficiency reduction in green LEDs
Solution Approach 1:
The invention changes the crystallographic orientation parameter from conventional c-plane to semipolar planes (specifically (10-11), (20-21), or (11-22) planes). This parameter change eliminates the quantum confined Stark effect and reduces piezoelectric polarization, thereby resolving the efficiency loss in green LEDs while maintaining manufacturability through established epitaxial growth techniques adapted to these new orientations.
2Loss of energy
If epitaxial growth is performed on semipolar planes to reduce polarization effects, then efficiency of green LEDs is improved, but the footprint of nitride materials increases and defect density increases
Solution Approach 1:
The invention applies local quality by creating patterned structures with specific local crystallographic orientations. By forming semipolar planes in controlled locations and orientations, the patent achieves reduced polarization effects in critical active regions while managing defect propagation through the structured approach. The semipolar orientation is strategically applied where it provides maximum benefit for reducing the quantum confined Stark effect.
3Manufacturing precision
If the footprint of nitride materials is reduced to minimize defects, then manufacturing precision is improved, but the area available for light emission is reduced
Solution Approach 1:
The invention transitions from two-dimensional planar growth to three-dimensional structured growth on semipolar planes. By utilizing the vertical dimension and creating patterned semipolar structures, the patent achieves better defect control through reduced footprint in the plane of the substrate while maintaining or enhancing emission area through the three-dimensional structure and increased active region volume.
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 reduces the density of extended defects and polarization effects, leading to improved efficiency of green LEDs, potentially reaching values closer to those of blue LEDs, thus bridging the 'green gap' in efficiency.
Implementation Method 1
Epitaxial growth of said layer starting from said facets having a {111} crystal orientation
Implementation Method 2
there is piezoelectric polarization of the crystal as a result of a mechanical stress that develops in this particular crystal structure
Data Source
AI summary
A method making it possible to obtain, on an upper surface of a crystalline substrate, a semipolar layer of nitride material comprising any one from among gallium, aluminium or indium, the method comprises the following steps: obtaining, on the upper surface of the crystalline substrate, a plurality of parallel grooves which extend in a first direction, one of the two opposite facets exhibiting a crystal orientation; etching a plurality of parallel slices which extend in a second direction that has undergone a rotation with respect to the first direction of the grooves in such a way as to obtain individual facets exhibiting a crystal orientation; epitaxial growth of the material from the individual facets.