Semiconductor Light Emitting Device Side Surface Extraction
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Solution Overview
Problem
Conventional semiconductor light emitting devices with nitride-based semiconductor light emitting elements face challenges in achieving high light extraction efficiency due to the refractive index difference between the transparent substrate and the sealing resin, leading to significant light reflection and absorption, especially when using a transparent silicone resin as a die bonding paste.
Innovation Solution
A semiconductor light emitting device is developed with a transparent substrate, an adhesive layer containing a fluorescent substance, and a sealing member also containing a fluorescent substance, where the adhesive layer's thickness is equal to or smaller than the average particle diameter of the fluorescent substance in the sealing member, enhancing light extraction by wavelength conversion and altered reflection directions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a transparent silicone resin is used as die bonding paste, then ease of manufacture is improved, but light extraction efficiency deteriorates due to refractive index difference causing light reflection and absorption
Solution Approach 1:
A wavelength conversion layer is introduced between the light emitting element and the transparent substrate. This intermediary layer converts the wavelength of light that would otherwise be reflected or absorbed at the interface, thereby improving light extraction efficiency while maintaining the use of transparent silicone resin as die bonding paste
Solution Approach 2:
The patent changes the wavelength parameter of light through the wavelength conversion layer. By converting light to a different wavelength, the optical properties at the interface between transparent substrate and sealing resin are altered, reducing reflection and absorption losses
2Device complexity
If light is extracted from the upper surface of the light emitting element, then device structure is simplified, but light extraction efficiency deteriorates due to absorption by the light emitting layer and electrode layers
Solution Approach 1:
The patent shifts the light extraction direction from the vertical dimension (upper surface) to the horizontal dimension (side surface). By making the transparent substrate extend laterally and extracting light from the side surface, the light path avoids passing through the absorbing electrode layers and light emitting layer, thereby improving extraction efficiency
3Reliability
If the adhesive layer thickness is increased to ensure proper bonding, then bonding reliability is improved, but light extraction efficiency deteriorates due to increased absorption path
Solution Approach 1:
The patent changes the wavelength parameter of light through the wavelength conversion layer. By converting light to a different wavelength, the optical properties at the interface between transparent substrate and sealing resin are altered, reducing reflection and absorption losses
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 configuration improves light extraction efficiency by reducing re-absorption and enhancing light output from the side surface of the transparent substrate, while maintaining heat radiation characteristics, resulting in a semiconductor light emitting device with higher illuminance.
Implementation Method 1
an adhesive layer containing a fluorescent substance, for fixing the semiconductor light emitting element on the substrate
Implementation Method 2
the angle of total reflection (θside: if the light is incident on the side surface of substrate with this or larger angle with respect to the vertical direction, the light is totally reflected)
Data Source
AI summary
A semiconductor light emitting device includes: a semiconductor light emitting element including a transparent substrate; a reflective substrate on which the semiconductor light emitting element is mounted; an adhesive layer containing a fluorescent substance, for fixing the semiconductor light emitting element on the reflective substrate; and a sealing member containing a fluorescent substance, for sealing the semiconductor light emitting element. In the semiconductor light emitting device, the adhesive layer has a thickness equal to or smaller than average particle size of the fluorescent substance contained in the sealing member.