Red LED Capping Layer Structure for Higher Light Extraction
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Solution Overview
Problem
Semiconductor light emitting devices used for red wavelength applications face inefficiencies in light extraction, particularly in the red wavelength range of 620 nm to 750 nm, due to significant reflection and loss at interfaces between different refractive index materials.
Innovation Solution
A semiconductor light emitting device configuration that includes a capping layer with a refractive index between 2.05 and 2.58 and an encapsulation layer with a lower refractive index, strategically positioned to minimize reflection and maximize transmittance, along with a reflective layer on the side surfaces to enhance light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a conventional light emitting structure is used without optimized capping and encapsulation layers, then the device structure is simple, but light extraction efficiency is poor due to significant reflection and loss at interfaces
Solution Approach 1:
The patent introduces a capping layer with intermediate refractive index (2.05-2.58) between the semiconductor layer and encapsulation layer. This intermediate layer acts as a mediator that gradually transitions the refractive index, reducing the abrupt interface contrast that causes reflection. The capping layer with refractive index between the semiconductor and encapsulation layers minimizes optical reflection and maximizes light extraction efficiency.
Solution Approach 2:
The patent optimizes the refractive index parameter of the capping layer to be in the specific range of 2.05-2.58, and controls the thickness parameter to be 50-100 nm. By changing these physical parameters, the optical properties at the interface are improved, reducing reflection loss and enhancing light extraction efficiency in the red wavelength range.
2Loss of energy
If the capping layer thickness is too thin, then the device structure is compact, but reflection reduction effect is insufficient; if too thick, then light extraction efficiency improves, but device complexity increases
Solution Approach 1:
The patent specifies the capping layer thickness parameter to be within 50-100 nm to achieve optimal balance between reflection reduction and device simplicity. This parameter optimization ensures sufficient light extraction enhancement without excessive structural complexity.
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
Significantly increases light extraction efficiency in the red wavelength range by optimizing the refractive indices and positions of the capping and encapsulation layers, and the reflective layer, resulting in improved transmittance and reduced reflection, thereby enhancing the overall performance of the semiconductor light emitting device.
Implementation Method 1
a capping layer on a top surface of the light emitting structure and having a first refractive index in a range of about 2.05 to about 2.58; and an encapsulation layer on the capping layer and on the light emitting structure, and having a second refractive index which is less than the first refractive index
Data Source
AI summary
A semiconductor light emitting device, including a light emitting structure comprising a first semiconductor layer having a first conductivity type, a second semiconductor layer having a second conductivity type which is different from the first conductivity type, and an active layer between the first semiconductor layer and the second semiconductor layer and configured to emit light having a wavelength in a range of about 620 nm to about 750 nm; a first electrode electrically connected to the first semiconductor layer; a second electrode electrically connected to the second semiconductor layer; a capping layer on a top surface of the light emitting structure and having a first refractive index in a range of about 2.05 to about 2.58; and an encapsulation layer on the capping layer and on the light emitting structure, and having a second refractive index which is less than the first refractive index.