DUV LED Heterostructure Phonon Blocking and Light Extraction
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Solution Overview
Problem
Deep ultraviolet light emitting diodes (DUV LEDs) suffer from low external and wall plug efficiencies due to internal reflection and strong absorption in AlGaN and GaN layers, leading to reduced light extraction efficiency and quantum efficiency at higher currents and powers.
Innovation Solution
A light emitting heterostructure with an n-type contact layer and a light generating structure comprising multiple quantum wells, where the energy difference between the contact layer and quantum wells is greater than the polar optical phonon energy, and the structure's width is comparable to the mean free path for phonon emission, along with a blocking layer and a composite contact that includes a transparent adhesion layer and a reflecting metal layer to enhance light emission.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If AlGaN structures with high Al content are grown to achieve shorter wavelength UV emission, then the emission wavelength decreases, but material quality deteriorates due to low Al adatom mobility causing inhomogeneous composition, lateral phase separation, and high defect density
Solution Approach 1:
The patent divides the single high-Al-content AlGaN layer into multiple AlGaN quantum wells separated by lower-Al-content AlGaN barrier layers. This segmentation allows each quantum well to maintain high Al content for short wavelength emission while the barrier layers provide lower defect density regions that facilitate growth and reduce overall material defects.
Solution Approach 2:
Different regions of the heterostructure are assigned different Al compositions optimized for their specific functions: high Al content (30-50%) in quantum wells for short wavelength emission, and lower Al content (10-30%) in barrier layers for reduced defects and improved growth. This local quality differentiation resolves the contradiction between achieving short wavelength emission and maintaining material quality.
2Ease of manufacture
If conventional LED structures are used with sapphire substrate, then device fabrication is simplified, but light extraction efficiency is severely reduced due to internal reflection at sapphire/air interface
Solution Approach 1:
The patent introduces an electron blocking layer as an intermediary between the p-type contact layer and the quantum wells. This layer serves multiple functions: it blocks electrons from leaking into the p-type region, enhances light extraction by reducing internal reflection, and maintains compatibility with conventional sapphire substrate fabrication processes.
Solution Approach 2:
The patent modifies the energy band parameters by introducing the electron blocking layer with specific conduction band offset, which changes the electron transport characteristics and optical properties of the device. This parameter change enables improved light extraction efficiency while maintaining ease of manufacture on sapphire substrates.
3Power
If higher currents and generated powers are applied to increase output, then output power increases, but efficiency is reduced due to strong absorption in top AlGaN and GaN layers
Solution Approach 1:
The patent transitions from a planar LED structure to a vertical heterostructure with multiple quantum wells stacked in the growth direction. This dimensional change allows light to be generated and extracted more efficiently by utilizing the vertical dimension for electron injection and light extraction pathways, reducing absorption losses in the top layers even at high currents.
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 enhances electron transitions and confinement in quantum wells, improves light extraction efficiency, and increases the external and wall plug efficiencies of DUV LEDs, particularly at shorter wavelengths.
Implementation Method 1
enhanced transitions of the injected electrons into multiple quantum wells
Implementation Method 2
difference between an energy of the n-type contact layer and an electron ground state energy of a quantum well is greater than an energy of a polar optical phonon
Implementation Method 3
confinement of the injected electrons in the quantum wells
Implementation Method 4
a reflecting metal layer configured to reflect at least a portion of the light generated by the light generating structure
Implementation Method 5
improved light extraction efficiency
Data Source
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AI summary
A light emitting diode is provided, which includes an n-type contact layer and a light generating structure adjacent to the n-type contact layer. The light generating structure includes a set of quantum wells. The contact layer and light generating structure can be configured so that a difference between an energy of the n-type contact layer and an electron ground state energy of a quantum well is greater than an energy of a polar optical phonon in a material of the light generating structure. Additionally, the light generating structure can be configured so that its width is comparable to a mean free path for emission of a polar optical phonon by an electron injected into the light generating structure. The diode can include a blocking layer, which is configured so that a difference between an energy of the blocking layer and the electron ground state energy of a quantum well is greater than the energy of the polar optical phonon in the material of the light generating structure. The diode can include a composite contact, including an adhesion layer, which is at least partially transparent to light generated by the light generating structure and a reflecting metal layer configured to reflect at least a portion of the light generated by the light generating structure.