UVC LED Nanostructure Emitter for Short-Wavelength Efficiency
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Solution Overview
Problem
UVC LED devices face challenges with low wall plug efficiency, poor external quantum efficiency, and emission wavelengths that are too long for short-wavelength UVC applications, due to issues like non-radiative recombination centers, weak dipole moments, and transverse-magnetic mode polarized emission.
Innovation Solution
The solution involves selective area epitaxial growth of an AlGaN quantum well structure on n+ doped nanostructures, which diverts defect propagation, provides a non-polar surface, and angles transverse magnetic polarized emission to improve emission efficiency by growing the active layer on the sloped sidewalls of nanostructures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If nanowires are used to relieve strain to allow for large Al-content active layers, then emission wavelength reaches shorter UVC range, but area fraction of emitter layer is reduced
Solution Approach 1:
The patent transitions from planar emitter structures to three-dimensional nanowire arrays, utilizing vertical growth to achieve strain relief and short-wavelength emission while maintaining high area fraction through dense packing of nanowires across the substrate surface
Solution Approach 2:
The patent applies different structural characteristics to different regions: nanowire cores provide strain relief for short-wavelength emission, while the collective array of nanowires maintains high area fraction, and selective epitaxial growth on nanowire sidewalls provides defect-free active regions
2Illumination intensity
If dry etching is used to define growth areas on vertical fins, then TM polarized light extraction is improved, but surface damage occurs requiring wet etch step
Solution Approach 1:
The patent replaces mechanical/chemical etching processes with a self-organized nanowire growth approach, where nanowires are formed through selective epitaxial growth rather than etching, eliminating surface damage while maintaining vertical orientation for TM polarized light extraction
Solution Approach 2:
The nanowire structures self-organize during selective epitaxial growth to form vertical arrays with appropriate spacing, eliminating the need for etching-defined patterns and the associated surface damage problems
3Illumination intensity
If InGaN is used as active material, then visible spectrum emission is achieved, but UVC range emission is not obtained
Solution Approach 1:
The patent changes the material composition parameter from InGaN to AlGaN, specifically increasing aluminum content to achieve the desired emission wavelength in the UVC range while maintaining high emission intensity through optimized quantum well structures
Solution Approach 2:
The patent uses composite AlGaN quantum well structures with specific aluminum compositions (x in AlxGa1-xN) to achieve both short-wavelength UVC emission and high emission intensity, combining the benefits of wide bandgap materials for UV emission with optimized well structures for high efficiency
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 enhances the emission efficiency of UVC LEDs by reducing defects, improving photon collection, and increasing oscillator strength, leading to higher internal quantum efficiency and effective emission in the 200-350 nm range.
Implementation Method 1
LED devices emitting radiation in the UVC band... emission across the entire c-band with good internal quantum efficiency... light is emitted from said device
Implementation Method 2
a light reflective layer in contact with the top of at least a portion of said nanowires or nanopyramids... light reflective layer optionally acting as a second electrode; wherein in use light is emitted from said device in a direction substantially opposite to said light reflective layer
Data Source
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AI summary
A light emitting device for emitting UVC radiation. The device comprises a substrate and a patterned layer. The patterned layer comprises a plurality of mask regions on the substrate. Exposed portions of the substrate are disposed between the mask regions. A plurality of nanostructures are disposed on the exposed portions of the substrate and over the mask regions, the plurality of nanostructures being a single crystal semiconductor and comprising a core tip. An active layer is disposed over the plurality of nanostructures. The active layer is a quantum well structure and comprises at least one material chosen from AIN, AIGaN and GaN. A p-doped layer is disposed over the active layer. Both the active layer and the p-doped layer are conformal to the plurality of nanostructures so as to form an emitter tip over the core tip.