Cascaded Multi-Color III-Nitride LEDs With Tunnel Junction Control
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Solution Overview
Problem
Current III-nitride light-emitting diodes (LEDs) face challenges in achieving efficient monolithic, cascaded, multiple color emission due to high defect density, nonradiative surface recombination losses, and poor external quantum efficiency, especially at micro-sized scales, which limits their application in full-color display technologies.
Innovation Solution
A method for fabricating monolithic, cascaded, multiple color LEDs with independent junction control using epitaxial growth, where tunnel junctions connect LEDs with different emission wavelengths, and a higher growth temperature reduces defect density, followed by surface treatment and activation of p-type layers for independent control, enabling blue, green, and red emissions in a single device.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If traditional p-contacts are used in III-nitride LEDs, then device fabrication is simplified, but operating voltage increases significantly and current spreading is poor
Solution Approach 1:
The patent introduces an n-type tunnel junction layer as an intermediary between the p-type GaN layer and the subsequent n-type LED structure. This tunnel junction serves as a mediator that enables low-resistance electrical contact while maintaining the benefits of p-type GaN for current spreading, thus resolving the contradiction between fabrication simplicity and operating voltage reduction.
Solution Approach 2:
The patent changes the electrical parameters of the GaN layer by creating a highly doped n-type tunnel junction region with specific doping concentrations (1×10^19 to 1×10^21 atoms/cm³). This parameter change enables the tunnel junction to provide low resistance contact while the adjacent p-type GaN maintains its current spreading capability, resolving the voltage issue without sacrificing manufacturing ease.
2Ease of operation
If p+GaN is used as current spreading layer, then current distribution is improved, but electrical contact is difficult to achieve and hole concentration is low
Solution Approach 1:
The patent segments the device structure into distinct functional regions: a p-type GaN layer for current spreading, an n-type tunnel junction layer for electrical contact, and n-type LED regions for light emission. This segmentation allows each layer to optimize its specific function without compromise, enabling both effective current spreading and reliable electrical contact.
Solution Approach 2:
The n-type tunnel junction acts as an intermediary layer between the p-type GaN current spreading layer and the n-type LED structure. This intermediary enables electrical contact through the p-type layer without compromising its current spreading function, as the tunnel junction provides a low-resistance pathway while the p-type GaN maintains hole injection and lateral current distribution.
3Area of moving object
If micro-sized LED structure is used, then device size is reduced for display applications, but defect density increases and external quantum efficiency decreases
Solution Approach 1:
The patent changes the growth parameters by using higher temperatures (1000-1200°C) for the n-type LED layers compared to the tunnel junction layer. This parameter change reduces defect density in the micro-sized LED structures by promoting better crystal quality during growth, thereby maintaining external quantum efficiency despite the reduced device size.
Solution Approach 2:
The patent applies different growth conditions to different regions: the tunnel junction is grown at lower temperatures optimized for tunneling properties, while the n-type LED regions are grown at higher temperatures optimized for low defect density and high quantum efficiency. This local quality differentiation allows micro-sized devices to maintain high performance.
4Use of energy by moving object
If tunnel junction is implemented to enable current spreading, then operating voltage is reduced, but manufacturing complexity increases due to additional growth steps
Solution Approach 1:
The patent merges the tunnel junction formation with the epitaxial growth process itself, using MOCVD to grow the highly doped n-type GaN layer in-situ on the p-type GaN layer. This combining of functions eliminates the need for separate tunnel junction fabrication steps, reducing manufacturing complexity while maintaining the voltage-reducing benefits of the tunnel junction structure.
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 approach successfully integrates blue, green, and red LEDs on a wafer-scale with improved efficiency and independent control, overcoming the limitations of traditional p-contacts and reducing operating voltage, thus enhancing the performance of micro-sized LEDs for next-generation display applications.
Implementation Method 1
A tunnel junction is a diode comprised of a very highly doped (n+/p+) interface that allows for electrons to tunnel between the valence band and conduction band
Implementation Method 2
A higher growth temperature for an n-type III-nitride layer than the TJs is used to reduce defect density
Implementation Method 3
After growth of the LEDs, a surface treatment is performed to remove residual Mg
Implementation Method 4
The p-type III-nitride layer of one or more of the LEDs is activated after exposing access points by etching a mesa
Data Source
AI summary
A method of fabricating a plurality of monolithic, cascaded, multiple color III-nitride light-emitting diodes (LEDs) with independent junction control, wherein: each of the LEDs is comprised of at least an n-type III-nitride layer, a III-nitride emitting layer, and a p-type III-nitride layer; at least two of the LEDs are separated by an n-type tunnel junction (TJ) insertion layer grown by selective area growth on or above the p-type III-nitride layer of one of the LEDs; the p-type III-nitride layer of one of the LEDs and the n-type tunnel junction insertion layer form a tunnel junction; and the p-type III-nitride layer of one of the LEDs is at least partially covered by the n-type tunnel junction insertion layer.