Edge-Emitting Semiconductor Laser With Intermediate Cladding Layer
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Solution Overview
Problem
Existing edge-emitting semiconductor laser chips face challenges in optimizing stress and wave guidance, particularly for longer wavelengths where increased indium and aluminum content leads to lattice mismatch and material quality issues, and for shorter wavelengths where GaN substrates absorb strongly, limiting service life and performance.
Innovation Solution
The edge-emitting semiconductor laser chip incorporates an intermediate layer with a low refractive index, such as silicon nitride or silicon oxide, to act as a cladding layer, reducing substrate modes and allowing for targeted stress management and increased fill factor in the active zone, while also providing electrical contact and adhesion between the carrier substrate and the epitaxially grown component structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the emission wavelength is shifted towards blue or green (increased indium content in active zone), then the emission wavelength range is extended, but the lattice mismatch between AlGaN cladding layer and InGaN active zone increases, resulting in strong stresses that limit material quality
Solution Approach 1:
The patent introduces a composition gradient layer between the AlGaN cladding layer and the InGaN active zone. This intermediate layer has a gradual change in aluminum content, acting as a transition zone that mediates the lattice mismatch between the two materials. The gradient structure reduces dislocation density and stress accumulation, thereby improving material quality while maintaining the desired emission wavelength range.
Solution Approach 2:
The patent employs a composition gradient layer where the aluminum content varies continuously from the AlGaN cladding layer to the InGaN active zone. By changing the compositional parameter gradually rather than abruptly, the lattice mismatch is reduced step-by-step, minimizing stress and dislocation formation. This parameter gradient approach enables extended wavelength range while maintaining high material quality.
2Reliability
If a higher proportion of aluminum and greater layer thickness are used in AlGaN cladding layers for longer wavelengths, then wave guidance is improved, but the lattice mismatch with the active zone increases, resulting in strong stresses that limit material quality
Solution Approach 1:
The patent applies local quality by creating a composition gradient layer with spatially varying aluminum content. The cladding region maintains high aluminum content for effective wave guidance, while the gradient transitions to lower aluminum content near the active zone to reduce lattice mismatch. This local variation in composition allows simultaneous optimization of wave guidance and material quality in different regions of the laser structure.
Solution Approach 2:
The patent uses parameter changes by implementing a continuous gradient in aluminum concentration across the cladding layer thickness. The aluminum content parameter varies from high values at the outer cladding interface (for wave guidance) to lower values at the active zone interface (for lattice matching). This gradual parameter transition resolves the contradiction between wave guidance requirements and material quality constraints.
3Strength
If GaN substrates are used for shorter wavelength lasers, then the substrate is available and mechanically stable, but the substrate absorbs strongly at these wavelengths, limiting service life and performance
Solution Approach 1:
The patent extracts the absorbing GaN substrate from the final laser structure by growing the laser on a sacrificial GaN layer that is later removed. The GaN substrate serves only as a temporary growth platform during manufacturing, providing mechanical stability during fabrication. After the laser structure is grown, the sacrificial GaN layer is etched away, leaving the laser suspended or transferred to a non-absorbing support structure, thereby eliminating the absorption issue while retaining the mechanical benefits during manufacturing.
Solution Approach 2:
The patent applies preliminary action by using the GaN substrate exclusively during the epitaxial growth phase. The substrate provides necessary mechanical support and crystal orientation during laser fabrication. Once the laser structure is complete, the substrate is removed before the laser enters service, ensuring that the absorbing material never contacts the laser beam during operation. This temporal separation resolves the contradiction between manufacturing needs and operational performance.
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 design enhances the laser's performance by reducing stress, increasing the fill factor in the active zone, and improving wave guidance, enabling longer service life and better optical properties across various wavelengths without the need for thick AlGaN cladding layers.
Implementation Method 1
the intermediate layer has, for example, a significantly lower refractive index than the semiconductor material surrounding it. Due to the low refractive index of the intermediate layer, the optical wave generated in the semiconductor laser chip is shielded from the carrier substrate
Implementation Method 2
when the edge-emitting semiconductor laser chip is energized, electromagnetic radiation is generated and/or amplified in this active zone
Data Source
Figure 1A~1C
Figure 2A~2C
Figure 3A~3B
AI summary
The chip has a carrier substrate (1), and an intermediate layer (2), which imparts a bond between the carrier substrate and a component structure (50) of the chip. The intermediate layer is electrically insulated. The component structure comprises an active zone (5) for generating irradiation. The intermediate layer forms a part of a cover layer (3, 30) of the chip. The intermediate layer places an electrical contact between the carrier substrate and the active zone.