Symmetrical Quantum Well Active Layer for Yellow-Red Emission
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Solution Overview
Problem
Gallium-nitride based quantum wells face challenges in achieving high internal quantum efficiency, particularly in the yellow and red spectral regimes due to charge separation and reduced electron-hole wavefunction overlap as the emission wavelength extends beyond the green spectral regime.
Innovation Solution
A symmetrical quantum well active layer is introduced, featuring a thin inner layer of InN sandwiched between thicker outer layers of InGaN, creating a large heterojunction and enhancing electron-hole wavefunction overlap, which extends the emission wavelength into the yellow and red spectral regimes with increased spontaneous emission rate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the emission wavelength is extended beyond the green spectral regime into yellow and red regimes, then the emission wavelength range is expanded, but the internal quantum efficiency deteriorates due to charge separation and reduced electron-hole wavefunction overlap
Solution Approach 1:
The patent applies asymmetry by introducing a central low-bandgap delta-layer within the quantum well structure. This creates an asymmetric potential profile that counteracts the polarization-induced charge separation, allowing electrons and holes to overlap more effectively even at longer wavelengths in the yellow and red spectral regimes.
Solution Approach 2:
The patent changes the bandgap parameter by incorporating a low-bandgap delta-layer (InN or InGaN) with different compositional parameters than the surrounding barrier layers. This parameter modification creates favorable potential profiles that enhance carrier confinement and wavefunction overlap, maintaining high internal quantum efficiency across extended wavelength ranges.
2Device complexity
If a conventional quantum well structure is used, then the device structure is simple, but the electron-hole wavefunction overlap is reduced leading to low spontaneous emission rate
Solution Approach 1:
The central low-bandgap delta-layer acts as an intermediary element within the quantum well. It mediates the interaction between electrons and holes by creating a favorable potential landscape that enhances their spatial overlap, thereby increasing the spontaneous emission rate without requiring complex external structures.
Solution Approach 2:
The patent employs composite material structure by combining different nitride materials (GaN barrier layers, InGaN active layer, and InN or InGaN delta-layer) with different bandgap characteristics. This composite approach creates optimized potential profiles that enhance carrier confinement and wavefunction overlap, significantly improving the spontaneous emission rate.
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 symmetrical quantum well design significantly enhances electron-hole wavefunction overlap and spontaneous emission rate, effectively extending the emission wavelength into the yellow and red spectral regimes, improving the internal quantum efficiency of semiconductor LEDs.
Implementation Method 1
A quantum well is a potential boundary that confines particles to a planar, substantially two dimension region. The two-dimensional confinement increases bound energy of Coulombic electron, and hole attraction so that excitons occur under heat energy at room temperature.
Implementation Method 2
A quantum well can be formed as part of a semiconductor by having a material, such as indium gallium nitride (InGaN), sandwiched between two layers of a larger bandgap material such as gallium nitride (GaN).
Data Source
AI summary
A symmetrical quantum well active layer provides enhanced internal quantum efficiency. The quantum well active layer includes an inner (central) layer and a pair of outer layers sandwiching the inner layer. The inner and outer layers have different thicknesses and bandgap characteristics. The outer layers are relatively thick and include a relatively low bandgap material, such as InGaN. The inner layer has a relatively lower bandgap material and is sufficiently thin to act as a quantum well delta layer, e.g., comprising approximately 6 Å or less of InN. Such a quantum well structure advantageously extends the emission wavelength into the yellow/red spectral regime, and enhances spontaneous emission. The multi-layer quantum well active layer is sandwiched by barrier layers of high bandgap materials, such as GaN.