GaN LED Substrate Orientation for Polarized Light Extraction
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Solution Overview
Problem
Conventional light emitting diodes (LEDs) based on c-plane GaN suffer from internal polarization fields, leading to poor radiative recombination efficiency and reliability issues, particularly in achieving high intensity green LEDs, and exhibit 'roll-over' at higher current densities, limiting their efficiency and yield in general illumination applications.
Innovation Solution
The use of GaN substrates with unique shapes and orientations to determine and align strong and weak dipole planes, allowing for the efficient fabrication and packaging of LEDs that emit partially or fully polarized electromagnetic radiation, enhancing light intensity and handling efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional c-plane GaN substrates are used for LED fabrication, then manufacturing process is straightforward, but internal polarization fields cause poor radiative recombination efficiency and reliability issues
Solution Approach 1:
The patent changes the crystallographic orientation parameter of the GaN substrate from conventional c-plane to semi-polar or non-polar orientations. This parameter change eliminates the strong internal polarization fields present in c-plane substrates, thereby improving radiative recombination efficiency and device reliability while accepting increased fabrication complexity
Solution Approach 2:
The patent introduces asymmetric substrate orientations (semi-polar and non-polar) to break the symmetric c-plane structure. This asymmetry in crystal orientation fundamentally changes the polarization field distribution, reducing internal fields and improving carrier recombination efficiency at the cost of more complex device handling and alignment
2Illumination intensity
If increased indium content is used in InGaN layers to achieve longer wavelength emission, then green LED performance improves, but crystal quality is degraded due to reduced growth temperature requirements
Solution Approach 1:
The patent changes the substrate orientation parameter to semi-polar or non-polar GaN, which modifies the strain distribution and growth conditions in InGaN layers. This enables higher indium content to be incorporated while maintaining crystal quality, as the altered substrate orientation reduces misfit dislocations and improves layer structure even at reduced growth temperatures
Solution Approach 2:
The patent applies local quality control by optimizing the InGaN layer structure specifically for semi-polar or non-polar orientations. This localized optimization allows high indium content regions to maintain crystal quality through tailored growth conditions and layer design appropriate to the specific substrate orientation
3Productivity
If conventional LED packaging is used, then manufacturing is simple, but system efficiency is reduced due to misalignment of dipole planes with packaging structures
Solution Approach 1:
The patent performs preliminary action by determining the strong and weak dipole plane orientations of each LED device before packaging. This advance knowledge allows the packaging structure to be specifically designed and aligned to match the dipole planes, maximizing light extraction efficiency and system performance while accounting for individual device variations
Solution Approach 2:
The patent applies local quality optimization by tailoring the packaging approach to each individual LED device's specific dipole plane orientation. Rather than using a generic packaging solution, the packaging structure is locally optimized for each device's unique orientation characteristics, improving overall system efficiency
4Power
If blue LEDs are operated at higher current densities for general illumination, then light output increases, but efficiency drops off significantly due to roll-over phenomenon
Solution Approach 1:
The patent changes the substrate orientation parameter to semi-polar or non-polar GaN, which fundamentally alters the current distribution and carrier injection characteristics. This parameter change suppresses the roll-over phenomenon by reducing polarization-induced field effects, allowing LEDs to maintain high efficiency even at the high current densities required for general illumination applications
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 enables the creation of LEDs with improved system efficiencies, particularly in applications requiring polarized light, such as LCD backlighting and general illumination, by maximizing light intensity and reducing packaging inefficiencies.
Implementation Method 1
LEDs that emit partially or fully polarized electromagnetic radiation
Implementation Method 2
determine and align strong and weak dipole planes
Data Source
AI summary
A GaN based light emitting diode device which emits polarized light or light of various degrees of polarization for use in the creation of optical devices. The die are cut to different shapes, or contain some indicia that are used to represent the configuration of the weak dipole plane and the strong dipole plane. This allows for the more efficient manufacturing of such light emitting diode based optical devices.