Semiconductor Light-Emitting Element with Porous Electrode
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Solution Overview
Problem
Semiconductor light-emitting elements, particularly those with nitride semiconductors on sapphire substrates, face challenges in achieving high light extraction efficiency due to large refractive index differences, leading to trapped light and degradation of crystal quality when attempting to enhance light output through surface processing or reflective structures.
Innovation Solution
A semiconductor light-emitting element design featuring a second electrode with voids of wavelength or less in width, formed by high-temperature heat treatment, which diffusely reflects light, reducing total internal reflection and enhancing light extraction efficiency without degrading crystal quality.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the light taking-out surface of the substrate is processed to be a dome shape or nano-convex-concave structure is formed, then light extraction efficiency is improved, but advanced processing techniques are required and crystal quality may be degraded
Solution Approach 1:
The patent introduces a porous layer in the semiconductor structure that contains numerous pores with diameters of 1 nm to 100 nm. This porous structure increases the light extraction efficiency by scattering and trapping light paths without requiring complex surface processing. The pores are formed during crystal growth rather than through post-growth processing, thus avoiding degradation of crystal quality.
Solution Approach 2:
The porous layer is formed during the crystal growth process itself, before final device fabrication. By incorporating the light extraction enhancement structure during epitaxial growth, the patent eliminates the need for subsequent complex surface processing steps that would compromise crystal quality.
2Loss of energy
If convex-concave structure is formed by processing substrate surface or semiconductor layer, then light extraction efficiency is improved, but crystal growth conditions and processing conditions are not compatible leading to degraded crystal quality
Solution Approach 1:
The patent employs a porous layer with nanoscale pores that is integrated into the semiconductor crystal structure. This porous structure provides effective light extraction enhancement while being compatible with standard crystal growth conditions, as the pores are formed during epitaxial growth rather than through subsequent processing.
Solution Approach 2:
The patent changes the structural parameters during crystal growth by controlling the formation of the porous layer with specific pore diameters (1 nm to 100 nm) and pore densities. By adjusting growth parameters such as temperature, pressure, and gas flow during epitaxial growth, the porous structure is formed without requiring separate processing steps.
3Temperature
If nitride semiconductor is formed on sapphire substrate, then high heat release property is achieved, but large refractive index difference causes light to be reflected and trapped in the semiconductor layer
Solution Approach 1:
The patent introduces a porous layer as an intermediary structure between the sapphire substrate and the nitride semiconductor active layer. This porous layer serves dual functions: it maintains the thermal management benefits of the sapphire substrate while simultaneously reducing light trapping by providing a gradient in refractive index and creating multiple light extraction paths through the porous structure.
Solution Approach 2:
The porous layer with its nanoscale pores creates a gradual transition in refractive index between the sapphire substrate and the nitride semiconductor layer. This gradient structure reduces total internal reflection and allows more light to escape from the semiconductor layer, thereby improving light extraction efficiency while maintaining the thermal advantages of the sapphire substrate.
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 design significantly improves light extraction efficiency by diffusely reflecting light, overcoming the limitations of traditional methods while maintaining crystal quality, and is particularly effective for nitride semiconductor-based elements on sapphire substrates.
Implementation Method 1
the voids of wavelength or less in width are formed in the second electrode, and light is diffusely reflected by the second electrode
Implementation Method 2
forming the voids having a width of a wavelength or less in a plane of the second electrode facing the second semiconductor layer by heat-treating the conductive film
Data Source
Figure 1A~1B
Figure 2~3B
Figure 4~5
AI summary
A semiconductor light-emitting element includes, a first semiconductor layer (120), a second semiconductor layer (140), a light-emitting layer (130) provided between the first semiconductor layer and the second semiconductor layer, a first electrode (160) connected to the first semiconductor layer, and a second electrode (150) provided on the second semiconductor layer. A side of the second electrode facing to the second semiconductor layer is composed of at least any one of silver and silver alloy. The second electrode has a void (210) having a width of emission wavelength or less of the light-emitting layer in a plane of the second electrode facing to the second semiconductor layer.