Nitride Semiconductor Light Emitting Device Stress Relaxation
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Solution Overview
Problem
Semiconductor light emitting devices formed on silicon substrates experience degradation and operational malfunctions due to tensile stress caused by thermal expansion, leading to cracks and defects, which reduce light emission efficiency and device reliability.
Innovation Solution
Incorporating a first stress application layer with a nitride semiconductor crystal and a support substrate with a higher thermal expansion coefficient than the nitride semiconductor crystal, which relaxes tensile stress and mitigates the formation of cracks and defects, thereby enhancing light emission efficiency and device stability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a semiconductor light emitting device is formed by epitaxial growth of a nitride semiconductor crystal on a silicon substrate, then manufacturing cost is reduced and manufacturing efficiency is improved, but tensile stress in the epitaxial crystal layer causes cracks and defects
Solution Approach 1:
A stress relaxation layer is introduced between the silicon substrate and the light emitting layer to act as an intermediary that absorbs and relaxes tensile stress, preventing stress transmission to the light emitting layer while maintaining the silicon substrate for cost-effective manufacturing
Solution Approach 2:
The stress relaxation layer is designed with specific material properties (different thermal expansion coefficient and lattice constant) to change the stress parameters in the device structure, transforming the harmful tensile stress into a manageable stress distribution that prevents crack formation
2Illumination intensity
If device operation at high current density is required, then light emission intensity is improved, but temperature increases causing thermal expansion stress that generates cracks and defects
Solution Approach 1:
The stress relaxation layer serves as a thermal and mechanical buffer between the light emitting layer and the substrate, absorbing thermal expansion stress generated during high current density operation and preventing stress-induced cracks
Solution Approach 2:
The stress relaxation layer is specifically selected with thermal expansion properties that compensate for thermal expansion mismatch between the nitride semiconductor layers and the silicon substrate, reducing thermal stress during high temperature operation
3Use of energy by moving object
If the light emitting layer has a larger lattice constant than the first semiconductor layer, then light emission efficiency is improved, but tensile stress from the support substrate increases causing cracks
Solution Approach 1:
The stress relaxation layer is positioned between the support substrate and the light emitting layer to intercept and relax tensile stress before it reaches the light emitting layer, allowing the light emitting layer to maintain its optimal larger lattice constant for high efficiency operation
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
The solution effectively suppresses the degradation of device characteristics and operational malfunctions caused by tensile stress, resulting in a semiconductor light emitting device with improved light emission efficiency and reliability, even under high current density and temperature conditions.
Implementation Method 1
the support substrate has a thermal expansion coefficient larger than a thermal expansion coefficient of a nitride semiconductor crystal
Implementation Method 2
The first stress application layer relaxes tensile stress applied from the metal layer to the second semiconductor layer
Data Source
AI summary
According to one embodiment, a semiconductor light emitting device includes: a first semiconductor layer of a first conductivity type; a second semiconductor layer of a second conductivity type; a light emitting layer; a conductive metal layer; and a first stress application layer. The first semiconductor layer contains a nitride semiconductor crystal and receives tensile stress in a (0001) plane. The second semiconductor layer contains a nitride semiconductor crystal. The light emitting layer has an average lattice constant larger than a lattice constant of the first semiconductor layer. The conductive metal layer has a thermal expansion coefficient larger than a thermal expansion coefficient of a nitride semiconductor crystal. The first stress application layer is provided between the second semiconductor layer and the light emitting layer. The first stress application layer relaxes tensile stress applied from the metal layer to the second semiconductor layer.