Infrared LED Electrode Layout for Low-Absorption InP Substrates
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Solution Overview
Problem
Infrared LED elements with emission wavelengths of 1000 nm or more face challenges in achieving high light extraction efficiency due to absorption of infrared light by high-concentration dopants in the InP substrate, and the complexity of the bonding process with a support substrate, which limits their manufacturing simplicity and efficiency.
Innovation Solution
An infrared LED element with a semi-insulating InP substrate, where the electrodes are formed on the same side as the semiconductor layers, reducing the need for current flow through the substrate and minimizing light absorption, and incorporating a reflective electrode and insulating layer to enhance light extraction, allowing for a simpler manufacturing process and increased efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the InP substrate is doped with high concentration to provide conductivity for current injection, then electrical conductivity is improved, but infrared light absorption increases due to free carriers
Solution Approach 1:
The patent divides the electrical conduction path from the light extraction path. Current is injected through the semiconductor layers without passing through the InP substrate, while light extraction remains through the substrate. This segmentation allows the substrate to be semi-insulating (reducing light absorption) while still providing electrical conductivity through alternative paths via the doped semiconductor layers.
Solution Approach 2:
The patent applies different doping concentrations to different regions: the InP substrate is doped at low concentration (semi-insulating) to minimize light absorption, while the semiconductor contact layers are doped at high concentration to provide electrical conductivity. This local differentiation of doping quality resolves the contradiction between conductivity and light transmission.
2Loss of energy
If a support substrate is bonded to the wafer to improve light extraction efficiency, then light extraction efficiency is improved, but manufacturing complexity increases
Solution Approach 1:
The patent extracts and removes the support substrate after the epitaxial growth process. By taking out the support substrate, the invention eliminates the need for complex bonding processes while maintaining the ability to achieve high light extraction efficiency through the semi-insulating InP substrate and optimized electrode configuration.
Solution Approach 2:
Instead of bonding an additional support substrate to improve light extraction, the patent inverts the approach by using the growth substrate itself (InP substrate) with semi-insulating properties as the light extraction medium. This eliminates the need for external support substrates and simplifies the manufacturing process.
3Loss of energy
If the InP substrate is made semi-insulating to reduce light absorption, then light extraction efficiency is improved, but electrical conductivity deteriorates
Solution Approach 1:
The patent segments the functional roles: the InP substrate handles light extraction (requiring semi-insulating properties), while the semiconductor contact layers handle electrical conduction (requiring high doping). This functional segmentation allows each component to be optimized for its specific purpose without compromise.
Solution Approach 2:
The semiconductor contact layers act as intermediaries between the electrical contacts and the active region. They provide the necessary electrical conductivity pathways without requiring the InP substrate itself to be conductive, thus allowing the substrate to remain semi-insulating for optimal light extraction.
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 results in an infrared LED element with high light extraction efficiency and a simplified manufacturing process, reducing absorption of infrared light within the substrate and enabling a low-profile, flip-chip configuration with improved light extraction area and efficiency.
Implementation Method 1
If the InP substrate includes a dopant doped in high concentration, the infrared light is absorbed by free carriers present in the InP substrate
Implementation Method 2
even if the electrode disposed on the back side of the InP substrate is made of a material that exhibits reflectivity
Data Source
AI summary
The infrared LED element has a peak wavelength in a range from 1000 nm to 2000 n m inclusive and includes: an InP substrate having a semi-insulating property; a first semicon ductor layer of a conduction type that is a p-type or an n-type, being formed on top of the In P substrate; an active layer formed on top of the first semiconductor layer; a second semico nductor layer of a conduction type different from the first semiconductor layer, being forme d on top of the active layer; a first electrode formed on top of the first semiconductor layer, being in an area where the active layer is not formed; and a second electrode formed on top of the second semiconductor layer, being disposed at a place apart from the first electrode in a direction parallel to a surface of the InP substrate.