Multi-Junction LED Tunnel Junction Structure for Lower Resistance
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Solution Overview
Problem
Infrared LEDs made of AlGaAs-based or GaAs-based materials face issues with light absorption and high series resistance, limiting their brightness and efficiency, especially in applications requiring high peak tunnel current density.
Innovation Solution
A multi-junction LED structure is developed with a tunnel junction comprising a highly doped p-type semiconductor layer made of InzAlX1Ga1−X1As, a first composition graded layer of AlX2Ga1−X2As, a highly doped n-type semiconductor layer of GaYIn1−YP, and a second composition graded layer of AlX3Ga1−X3As, which reduces lattice mismatch and light absorption, enhancing crystal quality and efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If AlGaAs-based or GaAs-based materials are used for infrared LEDs, then the LED can be manufactured with conventional processes, but the LED exhibits light absorption and high series resistance, limiting brightness and efficiency
Solution Approach 1:
The patent employs a composite material structure for the tunnel junction consisting of multiple semiconductor layers with different compositions (AlGaAs, GaInP, InGaAs) and doping types (p-type and n-type). This composite structure reduces light absorption and series resistance while maintaining manufacturability through conventional epitaxial growth processes.
Solution Approach 2:
The patent changes material parameters by introducing composition gradients (varying Al and In content) and doping concentration gradients across the tunnel junction layers. These parameter changes optimize the balance between electrical conductivity and optical transparency, reducing both series resistance and light absorption.
2Power
If materials with lower band gap are adopted to increase peak tunnel current density, then the peak tunnel current density increases, but light absorption increases and brightness is reduced
Solution Approach 1:
The patent applies local quality by creating spatial variations in material composition and doping within the tunnel junction. Different layers have optimized local properties: highly doped regions for high current density and composition-graded regions with wider band gaps for reduced light absorption. This local optimization resolves the contradiction between power and brightness.
Solution Approach 2:
The patent utilizes parameter changes by implementing composition gradients (X1, X2, X3 representing varying Al content) and doping concentration gradients across the tunnel junction layers. These gradual parameter transitions enable high peak tunnel current density in doped regions while maintaining low light absorption in graded regions with wider band gaps.
3Loss of energy
If the p-region and n-region of the tunnel junction are made thinner to reduce series resistance, then series resistance decreases, but manufacturing precision requirements increase
Solution Approach 1:
The patent introduces composition graded layers as intermediary structures between the highly doped p-type and n-type regions. These graded layers act as transition zones that facilitate the junction formation while allowing for more relaxed thickness control of the highly doped regions, thus reducing series resistance without excessively stringent manufacturing precision requirements.
Solution Approach 2:
The patent applies preliminary action by pre-forming composition graded layers with controlled thickness and gradient profiles before forming the highly doped thin regions. This preliminary structuring establishes a foundation that guides subsequent doping processes, enabling precise control of the final junction properties with reduced sensitivity to thickness variations.
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 improved brightness and reduced series resistance, achieving a 7.5% higher brightness and 0.43 V lower forward voltage compared to conventional LEDs, effectively addressing the limitations of prior art.
Implementation Method 1
a first composition graded layer, disposed on the highly doped p-type semiconductor layer, that is made of a material represented by AlX2Ga1-X2As, wherein X2 is greater than 0 and less than X1; a second composition graded layer, disposed on the highly doped n-type semiconductor layer opposite to the first composition graded layer, and that is made of a material represented by AlX3Ga1-X3As
Implementation Method 2
each of the p-region and the n-region should have a doping concentration greater than 1×10^19 cm^-3
Implementation Method 3
a multi-junction LED which includes multiple epitaxial structures connected in series with each other through tunnel junction(s) during epitaxial growth, is used to achieve a high peak tunnel current density
Implementation Method 4
multiple epitaxial structures connected in series with each other through tunnel junction(s) during epitaxial growth
Data Source
AI summary
A multi-junction light-emitting diode (LED) includes a first epitaxial structure, a second epitaxial structure and a tunnel junction structure disposed therebetween. The tunnel junction structure includes a InzAlX1Ga1−X1As highly doped p-type semiconductor layer wherein z ranges from 0 to 0.05, a AlX2Ga1−X2As first composition graded layer wherein X2 is greater than 0 and less than X1, a GaYIn1−YP highly doped n-type semiconductor layer and a AlX3Ga1−X3As second composition graded layer that are sequentially disposed on the first epitaxial structure in such order. A method for making the abovementioned multi-junction LED is also disclosed.