Strained Layer with Recesses for Optoelectronic Semiconductor Body
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Solution Overview
Problem
Optoelectronic semiconductor bodies often experience mechanical tension and cracking due to lattice mismatch and differing thermal expansion coefficients between the substrate and epitaxially grown layers, particularly when depositing non-lattice adapted semiconductors like AlGaN or InGaN on GaN substrates, leading to deflection and reduced performance.
Innovation Solution
The introduction of a tensioned layer with vertical recesses, followed by a further layer that fills these recesses and covers the tensioned layer, reduces mechanical tension and cracking by optimizing lattice constants and thermal expansion compatibility, thereby decoupling optical properties from the substrate and improving emission characteristics.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If non-lattice adapted semiconductors (AlGaN, InGaN) are deposited on GaN substrate, then the desired optical properties and device functionality are achieved, but mechanical tension and cracking occur due to lattice mismatch
Solution Approach 1:
The patent divides the continuous epitaxial layer into segments by creating recesses in the tensioned layer. This segmentation allows the layer to accommodate lattice mismatch stress locally at recess positions, preventing continuous cracking while maintaining the overall structural integrity and optical functionality of the semiconductor device.
Solution Approach 2:
The patent introduces an intermediate layer between the substrate and the tensioned layer. This intermediate layer acts as a mediator that gradually transitions the lattice constant from the substrate to the tensioned layer, reducing the abrupt lattice mismatch and thereby minimizing mechanical tension and cracking while still allowing the desired optical properties to be achieved.
2Illumination intensity
If the aluminum content in the tensioned layer is increased to achieve total reflection, then the index of refraction decreases and optical performance improves, but the lattice constant deviation from substrate increases and mechanical tension worsens
Solution Approach 1:
By segmenting the high-aluminum-content tensioned layer through recesses, the patent allows higher aluminum content (and thus lower refractive index for better total reflection) without incurring excessive mechanical tension. The recesses relieve stress locally, enabling the use of high-aluminum-content materials for optimal optical performance while maintaining mechanical stability.
Solution Approach 2:
The patent applies local quality by creating regions with different aluminum contents and structural properties. The tensioned layer has high aluminum content for optimal total reflection in most regions, while recess areas provide stress relief. This local variation in composition and structure allows optimization of both optical performance and mechanical stability in different spatial locations.
3Ease of manufacture
If epitaxial layers are grown directly on substrate, then the manufacturing process is simple, but deflection and cracking occur due to accumulated mechanical tension
Solution Approach 1:
The patent introduces an intermediate layer as a mediator between the substrate and the epitaxial layers. This intermediate layer serves as a buffer that accommodates lattice mismatch and reduces mechanical tension, preventing deflection and cracking. While this adds a step to the manufacturing process, it ensures surface planarity and device reliability, making the overall manufacturing more precise and controllable.
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 effectively reduces mechanical tension and cracking, enhances the optical properties of the epitaxial layer sequence, and improves the emission characteristics of optoelectronic devices like edge-emitting semiconductor lasers by creating a more stable and planar surface for further epitaxial growth.
Implementation Method 1
The entirety of the epitaxially grown semiconductor layers is designated as an epitaxial layer sequence. Such an epitaxial layer sequence can be deposited by means of epitaxy on a substrate.
Implementation Method 2
The tension occurs because the 'natural' lattice constants of the substrate and of the tensioned layer are different from one another. The greater the deviation of the lattice constants from layers which are epitaxially grown directly on one another, the stronger the tension between these layers in general.
Implementation Method 3
In a second epitaxy step, a further layer was applied to the tensioned layer, which fills up the at least one recess and at least regionally covers the tensioned layer.
Data Source
AI summary
An optoelectronic semiconductor body has a substrate that includes a strained layer that is applied to the substrate in a first epitaxy step. The strained layer includes at least one recess formed vertically in the strained layer. In a second epitaxy step, a further layer applied to the strained layer. The further layer fills the at least one recess and covers the strained layer at least in some areas.