GaN Light-Emitting Device Strain Relaxation via In Composition Gradient
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Solution Overview
Problem
Group III nitride semiconductor light-emitting devices face challenges in reducing strain in the light-emitting layer, which affects emission efficiency, as existing methods either reduce the light-emitting capability of well layers or do not sufficiently relax strain.
Innovation Solution
The light-emitting layer in the device features a MQW structure with pits extending from the electrostatic breakdown preventing layer to the light-emitting layer, where the In composition ratio of the first well layer nearest to the n-type cladding layer is reduced compared to other well layers, ensuring equal emission wavelengths and improved strain relaxation without compromising light-emitting function.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stress or pressure
If the In composition ratios of well layers closest to n-type and p-type cladding layers are reduced to relax strain, then strain relaxation is improved, but the light-emitting capability of these well layers deteriorates
Solution Approach 1:
The patent applies local quality by differentiating the In composition ratio adjustment strategy: only the first well layer from the n-type cladding layer has reduced In composition ratio (15-25%) while other well layers maintain higher In composition ratios (20-35%). This localized modification relaxes strain at the critical interface without compromising the light-emitting capability of other well layers, resolving the contradiction between strain relaxation and light emission.
2Stress or pressure
If pits are generated in the nESD layer to relax strain, then strain relaxation is improved, but the strain is not sufficiently eliminated
Solution Approach 1:
The patent uses parameter changes by modifying the In composition ratio of the first well layer to a specific range (15-25%), which fundamentally changes the lattice constant and strain distribution. This parameter modification, combined with pit formation, achieves sufficient strain relaxation that neither method alone can accomplish, as evidenced by the emission wavelength alignment across all well layers.
3Stress or pressure
If the In composition ratio of the first well layer is reduced to relax strain, then strain relaxation is improved, but the emission wavelength shifts to longer wavelength
Solution Approach 1:
The patent applies parameter changes by precisely controlling the In composition ratio of the first well layer within 15-25%, which simultaneously achieves strain relaxation and maintains emission wavelength compatibility. This specific parameter range ensures that the emission wavelength of the first well layer matches other well layers, preventing spectral broadening while relaxing strain.
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 emission efficiency and narrows the full width at half maximum of the emission spectrum, achieving improved light output with reduced strain and maintaining the light-emitting function of the first well layer.
Implementation Method 1
a MQW structure in which an InGaN well layer and a barrier layer are repeatedly deposited
Implementation Method 2
an In composition ratio of only first well layer from the n-type cladding layer of the well layers is reduced than In composition ratios of other well layers so that an emission wavelength of the first well layer is equal to emission wavelengths of the other well layers
Data Source
AI summary
An emission efficiency of a light-emitting device is improved by reducing strains applied to a light-emitting layer. On a sapphire substrate, an n-type contact layer, an nESD layer, an n-type cladding layer, a light-emitting layer, a p-type cladding layer, and a p-type contact layer, are sequentially deposited. The light-emitting layer has a MQW structure in which a layer unit of a well layer, a capping layer, and a barrier layer sequentially deposited is repeatedly deposited. Of the well layers, the In composition ratio of only first well layer is reduced than the In composition ratios of other well layers, and the In composition ratios of the other well layers are equal to each other. The In composition ratio of the first well layer is designed so that the emission wavelength of the first well layer is equal to the emission wavelengths of other well layers.