Impact Ionization UV LED With Protruding Electrodes
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Solution Overview
Problem
Wide bandgap semiconductors, such as GaN, face challenges in p-type doping, leading to inefficient light emission in UV LEDs due to defects and reduced hole generation, resulting in low wall plug efficiency and conversion efficiency.
Innovation Solution
The development of light-emitting devices that utilize a high field electrode with protruding electrode elements to accelerate carriers through impact ionization, eliminating the need for p-n junctions and p-type doped semiconductors, thereby enhancing light emission efficiency in the UV region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If p-type doping is used in wide bandgap semiconductors to achieve light emission, then hole generation is required, but doping efficiency deteriorates due to wider bandgap causing fewer ionized acceptors and holes
Solution Approach 1:
The patent extracts and eliminates the p-type doping process entirely from the device structure. Instead of relying on doped regions to generate holes, the invention uses a p-n junctionless architecture where electrons are injected from a cathode, accelerated through a drift region, and cause impact ionization directly in the active semiconductor layer, thereby generating electron-hole pairs without requiring p-type dopants.
Solution Approach 2:
The patent replaces the chemical doping mechanism with a physical field-based mechanism. Instead of using dopant atoms to generate carriers through ionization, the invention uses an electric field to accelerate electrons to high energies, which then cause impact ionization through mechanical collision processes, substituting chemical doping with a field-driven physical process.
2Adaptability or versatility
If aluminum or indium is added to GaN to adjust bandgap for UV emission, then wavelength tuning is achieved, but element segregation and dislocation density increase leading to poor material properties
Solution Approach 1:
The patent applies local quality by using different semiconductor materials with inherently different bandgap energies in different regions of the device. The active layer uses a wide bandgap material (such as GaN, AlGaN, or InGaN) optimized for UV emission, while the drift region uses a material with appropriate electrical properties. This allows wavelength tuning through material selection rather than compositional grading, avoiding segregation issues.
Solution Approach 2:
The patent employs composite material structures combining multiple semiconductor layers with different properties. The device includes a cathode, a drift region made from one semiconductor material, and an active layer made from another material with suitable bandgap for UV emission. This composite approach allows optimization of each layer for its specific function while avoiding the material quality degradation associated with high-aluminum-content AlGaN.
3Device complexity
If conventional p-n junction LED structure is used, then device simplicity is maintained, but wall plug efficiency remains low around 3-4% for deep UV emission
Solution Approach 1:
The patent segments the device into distinct functional regions: a cathode for electron injection, a drift region for electron acceleration and energy buildup, and an active layer for light generation through impact ionization. This segmentation allows each region to be optimized for its specific function, with the drift region specifically designed to accelerate electrons to the energies needed for efficient impact ionization in the active layer, thereby improving overall wall plug 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 enables more efficient light emission in the UV region by avoiding the limitations of p-type doping, achieving higher wall plug efficiency and conversion efficiency compared to conventional UV LEDs, and allowing for the use of various wide bandgap semiconductors without doping constraints.
Implementation Method 1
Light-emitting devices that utilize a high field electrode with protruding electrode elements to accelerate carriers through impact ionization
Implementation Method 2
excited by emitting electrons (field emission) and/or accelerating electrons into a semiconductor using a high electric field electrode
Data Source
AI summary
Light-emitting devices and methods for making light-emitting devices. A light-emitting device includes a high-field electrode, a collector electrode, and a light generating region. The collector electrode is operatively coupled to one side of the light generating region, and the high-field electrode is operatively coupled to another side of the light generating region opposite the collector electrode. The high-field electrode includes protruding electrode elements that extend into the light generating region and toward the collector electrode. The protruding electrode elements accelerate carriers in the light generating region in response to a voltage being applied between the high-field electrode and the collector electrode. The carriers have sufficient kinetic energy to create electron-hole pairs in the light generating region through impact ionization. When these electron-hole pairs recombine, at least a portion of the recombination events emit a photon with an energy corresponding to the bandgap of the light generating region.