Flip-Chip Red LED Structure With Sapphire Substrate and Reflective Electrodes
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Solution Overview
Problem
Existing red light emitting devices based on AlInGaP-based semiconductors face challenges in achieving a flip chip structure due to the absorption of red light by GaAs substrates, necessitating improved heat dissipation and luminous efficiency.
Innovation Solution
A red light emitting device with a flip chip structure is designed using a substrate, semiconductor stack, ohmic layers, connection electrode layers, and electrode pads, featuring AlInGaP-based semiconductor layers and a configuration that allows for efficient light transmission and reflection, with ohmic layers distributed to minimize light absorption and enhance current spreading.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a GaAs substrate is used for AlInGaP-based red light emitting devices, then the semiconductor layer can be grown effectively, but the GaAs substrate absorbs red light making flip chip structure impossible
Solution Approach 1:
The patent extracts and removes the GaAs substrate from the device structure, retaining only the AlInGaP-based semiconductor layers grown on it. This extraction eliminates the light absorption problem while preserving the beneficial epitaxial growth characteristics of GaAs substrates for the red light emitting structure.
Solution Approach 2:
The patent introduces a sapphire substrate as an intermediary replacement for the GaAs substrate. The sapphire substrate serves as a new growth platform that does not absorb red light, enabling both effective semiconductor layer growth and compatibility with flip chip structure while eliminating the original substrate's light absorption drawback.
2Loss of energy
If the GaAs substrate is removed to enable red light emission, then light absorption is eliminated, but heat dissipation performance deteriorates
Solution Approach 1:
The patent changes the substrate material parameter from GaAs to sapphire, which fundamentally alters both the optical properties (no red light absorption) and thermal properties (improved heat dissipation). This parameter change enables simultaneous achievement of reduced energy loss and better temperature management.
Solution Approach 2:
The patent creates a composite structure combining sapphire substrate with AlInGaP-based semiconductor layers. This composite material system integrates the optical transparency of sapphire in the red region with the excellent thermal conductivity and epitaxial growth properties, achieving both reduced light absorption and improved heat dissipation.
3Loss of energy
If ohmic layers are distributed to minimize light absorption, then luminous efficiency improves, but device structure complexity increases
Solution Approach 1:
The patent applies local quality by creating distributed ohmic layers at specific locations within the device structure where they provide both electrical functionality and optical benefits. The ohmic layers are strategically positioned to minimize light absorption paths while maintaining electrical connectivity, achieving improved luminous efficiency without excessive complexity through localized optimization rather than uniform structure.
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 design achieves improved luminous efficiency and enables flip-chip bonding for red light emission, addressing the heat dissipation and absorption issues of previous devices.
Implementation Method 1
The first connection electrode layer may transmit light generated from the active layer
Implementation Method 2
the second connection electrode layer may reflect light generated from the active layer
Data Source
Figure 1A
Figure 1B~2B
Figure 2C~4
AI summary
A light emitting device according to an embodiment includes: a substrate; a first conductivity type window layer and a mesa disposed on one region of the first conductivity type window layer, in which the mesa is a semiconductor stack including an active layer and a second conductivity type window layer; an adhesive layer disposed between the semiconductor stack and the substrate; a first ohmic layer electrically connected to the first conductivity type window layer; a second ohmic layer electrically connected to the second conductivity type window layer; and a first electrode pad and a second electrode pad disposed on the semiconductor stack to face the substrate, and electrically connected to the first ohmic layer and the second ohmic layer, respectively.