AlInP Green LEDs With Graded Buffer on GaAs
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Solution Overview
Problem
Current green-emitting LEDs face inefficiencies due to direct to indirect bandgap transitions and intervalley carrier transfer, limiting their ability to achieve high quantum efficiencies for green emission wavelengths, particularly around 560 nm, which is essential for high color rendering index in white light LEDs.
Innovation Solution
The use of Al1-xInxP layers with a compositionally-graded buffer to create a virtual substrate, allowing for growth of Al1-xInxP layers that maintain a direct bandgap at higher energies, preventing intervalley carrier transfer and enabling efficient green emission, while using inexpensive substrates like GaAs and reducing dislocation densities through strain relaxation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If (AlxGa1-x)yIn1-yP alloys are used for green emission, then lattice matching to GaAs is achieved, but direct to indirect bandgap transition occurs around 2.2-2.3 eV, reducing emission efficiency
Solution Approach 1:
The patent changes the compositional parameters of the alloy system by using Al1-xInxP with specific composition ranges (x=0.36-0.64) to maintain direct bandgap at higher energies while achieving lattice matching to GaAs substrates, thereby resolving the contradiction between ease of manufacture and emission efficiency
Solution Approach 2:
The patent employs composite material structure by creating Al1-xInxP alloy layers with compositionally-graded buffer layers, combining different material compositions to achieve both lattice matching and maintained direct bandgap properties for efficient green emission
2Illumination intensity
If green emission wavelength is reduced into the green range, then color rendering index is improved, but intervalley carrier transfer increases, lowering emission efficiency
Solution Approach 1:
The patent optimizes the bandgap energy parameter by using Al1-xInxP alloys with direct bandgap at higher energies (above 2.3 eV), which corresponds to green emission wavelengths around 560 nm, thereby improving color rendering while preventing intervalley carrier transfer and maintaining high emission efficiency
3Ease of manufacture
If Al1-xInxP layers are grown on GaAs substrates, then inexpensive substrates are used, but lattice mismatch causes dislocation densities to increase
Solution Approach 1:
The patent applies preliminary action by inserting compositionally-graded buffer layers between the GaAs substrate and the Al1-xInxP active layers. These buffer layers gradually transition the lattice constant, preventing dislocation formation and enabling high-quality growth of Al1-xInxP layers on inexpensive GaAs substrates
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 allows for high quantum efficiency green emission by maintaining a direct bandgap at higher energies, reducing intervalley carrier transfer, and enabling the growth of high-quality Al1-xInxP layers on inexpensive substrates, thus enhancing the performance of green LEDs.
Implementation Method 1
The buffer starts with a layer that is closely, but not necessarily exactly, lattice matched to GaAs, and then incrementally or otherwise increases the lattice constant in each sequential layer until a predetermined lattice constant of Al1-xInxP is reached
Data Source
AI summary
High bandgap alloys for high efficiency optoelectronics are disclosed. An exemplary optoelectronic device may include a substrate, at least one Al1-xInxP layer, and a step-grade buffer between the substrate and at least one Al1-xInxP layer. The buffer may begin with a layer that is substantially lattice matched to GaAs, and may then incrementally increase the lattice constant in each sequential layer until a predetermined lattice constant of Al1-xInxP is reached.