Semiconductor Light Emitting Device with Reflection Layer
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Solution Overview
Problem
Light-emitting diodes (LEDs) face challenges in light emitting efficiency due to total internal reflection at the chip-air interface, leading to significant photon loss and reduced external quantum efficiency.
Innovation Solution
A semiconductor light emitting device with a mesa and depression structure, incorporating a reflection layer that covers parts of the doped semiconductor layers and has a high reflectance of over 98%, ensuring that light emitted from the light emitting layer is effectively reflected and utilized, either by a single reflection layer or a combination of layers positioned to maximize light reflection without overlap when viewed perpendicular to the light emitting layer.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a conventional LED chip structure is used, then the device is simple to manufacture, but light extraction efficiency is low due to total internal reflection at the chip-air interface
Solution Approach 1:
The patent introduces a depression portion that extends downward from the mesa portion, creating a vertical dimension change in the chip structure. This dimensional change allows light to be extracted from the side walls of the depression, providing additional light extraction pathways beyond the traditional top surface, thereby reducing total internal reflection losses.
Solution Approach 2:
The patent introduces a reflection layer as an intermediary component between the semiconductor layers and the external environment. This reflection layer has high reflectance properties and is positioned to reflect light that would otherwise be lost due to total internal reflection, redirecting it toward the depression portion for extraction.
2Illumination intensity
If the thickness of the mesa portion is increased to improve light emission, then light extraction from the top surface improves, but light extraction from side surfaces deteriorates due to increased total internal reflection
Solution Approach 1:
By creating the depression portion extending downward from the mesa, the patent adds a vertical dimension for light extraction. This allows light to escape from the side walls of the depression at different angles and positions, compensating for the increased total internal reflection that occurs with thicker mesa structures.
Solution Approach 2:
The patent converts the harmful effect of total internal reflection at the chip-air interface into a beneficial effect by using the reflection layer to reflect previously lost photons back into the structure, where they can be extracted through the depression portion's side walls.
3Loss of energy
If a reflection layer with high reflectance is added to improve light extraction efficiency, then external quantum efficiency increases, but manufacturing complexity and cost increase
Solution Approach 1:
The reflection layer serves as an intermediary component that mediates between the semiconductor structure and the external environment, capturing and redirecting light that would otherwise be lost. This single added component addresses the photon loss issue without requiring complex structural modifications.
Solution Approach 2:
The patent changes the optical parameter of the interface by introducing a reflection layer with high reflectance properties. This parameter change (from low reflectance chip-air interface to high reflectance engineered interface) dramatically improves light extraction efficiency with a relatively simple manufacturing approach.
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 enhances light utilization efficiency by reflecting light emitted from the light emitting layer, increasing the external quantum efficiency and overcoming the limitations of total internal reflection, thereby improving the overall light emitting efficiency of LEDs.
Implementation Method 1
the reflection layer covers at least part of the second type doped semiconductor layer and at least part of the first type doped semiconductor layer, wherein observing from a viewing direction parallel to the light emitting layer, the reflection layer covers at least part of the first side surface and at least part of the second side surface
Implementation Method 2
Light emitting layer (120) disposed on the mesa portion (112)
Implementation Method 3
when photons generated by an active layer (light emitting layer) reach a chip and air interface and have an incident angle greater than a critical angle, a total internal reflection (TIR) is to occur
Data Source
AI summary
A semiconductor light emitting device including a first type doped semiconductor layer, a light emitting layer, a second type doped semiconductor layer, and a reflection layer is provided. The first type doped semiconductor layer has a mesa portion and a depression portion. The light emitting layer is disposed on the mesa portion and has a first surface, a second surface and a first side surface connecting the first surface with the second surface. The second type doped semiconductor layer is disposed on the light emitting layer and has a third surface, a fourth surface and a second side surface connecting the third surface with the fourth surface. Observing from a viewing direction parallel to the light emitting layer, the reflection layer covers at least part of the first side surface and at least part of the second side surface. A flip chip package device is also provided.