AlInN-GaN DBR with Gradient Transition Layer for Crack Reduction
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Solution Overview
Problem
The manufacturing of semiconductor multilayer film reflecting mirrors for vertical cavity light-emitting elements often results in high densities of micro cracks and threading dislocations, which reduce the crystallinity and optical output, making it difficult to achieve high reliability.
Innovation Solution
A semiconductor multilayer film reflecting mirror is formed by alternately growing AlInN and GaN layers with an inter-film transition layer, using metal organic chemical vapor deposition, to reduce dislocation density and improve crystallinity, employing specific growth temperatures and gas transitions to optimize layer composition and thickness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If semiconductor thin films are layered to manufacture a multilayer film reflecting mirror, then the reflectivity is improved, but defects such as micro cracks and threading dislocations occur at high density
Solution Approach 1:
An inter-film transition layer is introduced between the AlInN layer and GaN layer. This transition layer acts as an intermediary that gradually changes the crystal structure and composition, reducing the thermal stress and lattice mismatch between the two materials. The transition layer includes an AlGaN layer with aluminum content gradually decreasing from the AlInN interface toward the GaN interface, which effectively reduces dislocation density and prevents micro crack formation while maintaining high reflectivity.
Solution Approach 2:
The invention changes the composition parameter (aluminum content) gradually through the transition layer. The aluminum content decreases from approximately 18% at the AlInN interface to 0% at the GaN interface, creating a gradient structure. This gradual parameter change reduces the abrupt thermal stress and lattice mismatch, thereby reducing dislocation density and defect formation while preserving the optical properties needed for high reflectivity.
2Shape
If high-temperature GaN layer is formed to improve flatness and reduce micro cracks, then the surface quality is improved, but threading dislocations occur at high density
Solution Approach 1:
The invention applies different quality characteristics to different regions of the film structure. The transition layer has a gradient aluminum content distribution, with higher aluminum content near the AlInN interface (providing stress relief) and lower aluminum content near the GaN interface (providing good lattice matching). This local variation in composition allows the structure to simultaneously achieve good flatness and low dislocation density.
Solution Approach 2:
The invention creates a composite structure consisting of AlInN layer, transition layer with gradient AlGaN composition, and GaN layer. This composite material approach combines the advantages of different materials: AlInN provides high refractive index for reflectivity, while the gradient AlGaN transition layer provides stress management and lattice matching, and GaN provides excellent flatness and low defect density.
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 significantly reduces dislocation density, enhancing the reflectivity and optical output of the semiconductor multilayer film reflecting mirror, thereby improving the reliability of the vertical cavity light-emitting element.
Implementation Method 1
metal organic chemical vapor deposition
Implementation Method 2
an AlInN layer and a GaN layer are alternately grown
Data Source
Figure 1~2
Figure 3
Figure 4~5A
AI summary
Provided is a semiconductor multilayer film reflecting mirror formed by alternately repeating a first nitride film containing In (indium) and a second nitride film not containing In. The reflecting mirror (15) includes an inter-film transition layer (15C) between the first and second nitride films, the composition of which is varied from the composition of the first nitride film to the composition of the second nitride film. The inter-film transition layer has a first transition layer (15C1) formed on the first nitride film and containing In and Al (aluminum), and a second transition layer (15C2) formed on the first transition layer and containing Al but not containing In. In the first transition layer, the percentages of In and Al are decreased from the first nitride film to the second transition layer, and the percentage of In in the first transition layer starts to decrease at a same or closer position to the first nitride film than the percentage of Al. The mirror is a DBR reflecting in the blue and reducing the number of micro-cracks in the device. The DBR (15) may be integrated into a VCSEL (10), the VCSEL comprising a GaN substrate (11), a GaN buffer layer (13), the DBR (15), a p-clad layer (17), an active layer (20), an upper clad layer p-AlGaN (21), a p-GaN layer (23) and a p-GaN contact layer (25). The first nitride film (15A) may be made from AlInN, the first transition layer (15C1) from AlGaInN, the second transition layer (15C2) from AlGaN and the second nitride film (15B) from GaN.