Transparent Spacer Reduces Phosphor Light Absorption in LED
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Solution Overview
Problem
Phosphor light absorption by GaN-based LED dies results in significant light loss, as about 15% of the phosphor light impinging on the LED surface is absorbed, leading to a substantial reduction in light extraction efficiency.
Innovation Solution
A transparent glass plate with a thickness of at least 250 microns is affixed over the LED die, and a phosphor layer is deposited on the glass plate and its sidewalls, allowing phosphor light to pass through and exit from the glass plate's sidewalls rather than being absorbed by the LED die, thereby reducing absorption and increasing light extraction efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If phosphor layer is deposited directly over LED die surface, then device structure is simple, but light extraction efficiency is reduced due to absorption by LED material
Solution Approach 1:
A transparent substrate is introduced as an intermediary layer between the LED die and phosphor layer. This substrate has optical properties that reduce absorption of phosphor light by the LED material, thereby improving light extraction efficiency while maintaining manufacturing simplicity
Solution Approach 2:
The patent utilizes the thickness dimension of the transparent substrate (at least 250 microns) to create optical path differences. By controlling the substrate thickness, phosphor light can exit through sidewalls rather than being absorbed by the LED die, effectively using dimensional parameters to resolve the contradiction
2Loss of energy
If transparent substrate with thickness at least 250 microns is introduced between LED die and phosphor layer, then light extraction efficiency is improved, but device complexity and manufacturing steps increase
Solution Approach 1:
The transparent substrate serves multiple functions simultaneously: it acts as a mechanical support for the LED die, an optical element to reduce absorption, and a structural component for mounting. This multi-functionality reduces the need for additional separate components, thereby limiting the increase in device complexity
3Ease of manufacture
If phosphor layer is deposited directly on LED die, then manufacturing process is simple, but about 7.5% of phosphor light is wasted by absorption
Solution Approach 1:
The transparent substrate acts as a mediator that separates the phosphor layer from the LED die, reducing direct absorption of phosphor light by the LED material while maintaining a relatively simple manufacturing process through conventional mounting techniques
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 approach results in a 16% gain in light extraction efficiency compared to conventional methods where the phosphor layer is directly deposited on the LED die, with increased side emission and reduced absorption, enhancing the overall light output.
Implementation Method 1
Glass has an index of refraction of about 1.5... much of the phosphor light that enters the glass plate will exit from the sidewalls of the glass plate without contacting the LED die. Therefore, the absorption by the LED material will be much less compared to if the phosphor were directly deposited on the LED die.
Implementation Method 2
The blue light exciting the phosphor causes the phosphor to emit photons in all directions.
Data Source
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Figure 4~6
AI summary
To reduce absorption by an LED die (12) of light emitted by a phosphor layer (48), the absorbing semiconductor layers of the LED die (12) are separated from the phosphor layer by a relatively thick glass plate (44) affixed to the LED die or by the LED die transparent growth substrate. Therefore, phosphor light emitted at a sufficient angle towards the LED die will pass through the transparent spacer (44) and exit the sidewalls of the spacer, preventing the light from being absorbed by the LED die. The LED die may be GaN based. The spacer is at least 100 microns thick. A 16% gain in light extraction is achievable using the technique compared to the light emission where phosphor is directly deposited on the LED semiconductor layers.