Semiconductor Light Emitting Device External Optical Element
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Solution Overview
Problem
Semiconductor light-emitting devices, such as LEDs, face reduced light extraction efficiency due to total internal reflection and absorption by the semiconductor stack, especially in small chip designs where a significant portion of the surface area is occupied by light-impermissible pads, leading to heat dissipation challenges and inefficient light directionality.
Innovation Solution
Incorporating an external optical element with a refractive index larger than or similar to the transparent substrate, which surrounds the light-emitting structure, reduces light absorption and enhances thermal dissipation by contacting the environmental medium or heat dissipation materials, and features rough or uneven surfaces to minimize total reflection and increase light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If a reflective layer is formed between the epitaxy layer and substrate to reflect light, then light directionality is improved, but light extraction efficiency deteriorates due to multiple passes through the active layer causing absorption
Solution Approach 1:
The patent removes the reflective layer from between the epitaxy layer and substrate, extracting the harmful element that causes light absorption. Instead, a transparent substrate is used that allows light to pass through without reflection, eliminating the resonance effect that causes energy loss while still achieving light directionality through other means.
Solution Approach 2:
A transparent substrate is introduced as an intermediary element between the epitaxy layer and the external environment. This transparent substrate has refractive index characteristics that prevent total internal reflection, allowing light to escape efficiently without being reflected back into the active layer, thus mediating between light generation and light extraction.
2Loss of energy
If the substrate is made transparent to allow light emission, then light extraction efficiency is improved, but thermal dissipation capability deteriorates
Solution Approach 1:
The patent applies different properties to different regions: the substrate is made transparent in the optical path region to improve light extraction, while maintaining thermal conduction properties in the substrate structure to enable heat dissipation. The transparent substrate selectively transmits light while the overall device structure provides thermal management pathways.
3Area of moving object
If small chip size is used to reduce device footprint, then device compactness is improved, but light extraction efficiency deteriorates due to larger pad area ratio causing more light reflection and absorption
Solution Approach 1:
The patent converts the harmful effect of light reflecting off pads into a beneficial outcome. By using a transparent substrate with specific refractive index characteristics, light that would normally reflect off pads and be absorbed is instead allowed to pass through the substrate and escape, transforming the pad reflection problem into an opportunity for additional light extraction pathways.
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 significantly improves light extraction efficiency by reducing absorption within the semiconductor stack and enhances thermal management, making the semiconductor light-emitting device suitable for high-brightness, low-power, thin, and lightweight applications, particularly in back light units for liquid crystal displays.
Implementation Method 1
The refractive index of the external optical element is larger than or about the same as that of a transparent substrate of a light-emitting structure, or in-between that of the transparent substrate and an encapsulant
Implementation Method 2
When the refractive index of the environmental medium is less than that of the LED 100 and the incident angle is larger than the critical angle, the first ray R1 can be reflected totally at the boundary of the LED 100
Implementation Method 3
When the p-n junction receives a suitable forward voltage, the holes of the p-type semiconductor layer and the electrons of the n-type semiconductor layer are combined to emit light
Implementation Method 4
When the p-n junction receives a suitable forward voltage, the holes of the p-type semiconductor layer and the electrons of the n-type semiconductor layer are combined to emit light
Implementation Method 5
The bottom of the light-emitting structure contacts with the environmental medium or the heat dissipation material for increasing thermal efficiency by thermal convection and thermal conduction
Implementation Method 6
features rough or uneven surfaces to minimize total reflection and increase light extraction efficiency
Data Source
AI summary
This invention discloses a light emitting semiconductor device including a light-emitting structure and an external optical element. The optical element couples to the light-emitting structure circumferentially. In addition, the refractive index of the external optical element is greater than or about the same as that of a transparent substrate of the light-emitting structure, or in-between that of the transparent substrate and the encapsulant material.