Single-Face LED Electrode Layout for Compact μLED Pixels
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Solution Overview
Problem
The challenge in producing display screens with self-illuminating pixels using solid-state LEDs is to reduce pixel size and spacing while maintaining efficiency, as existing solutions like mesa structures lead to decreased external quantum efficiency and mutual optical couplings.
Innovation Solution
A light-emitting diode with a lateral P-N junction configuration, where a third region with opposite conductivity forms a stack with the first and second regions, creating a space charge region that enhances carrier recombination in the central area and prevents border recombinations, and a mesa structure that confines photons and reduces non-radiative recombinations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If mesa structure is used to make electrical contacts on N-type and P-type regions, then electrical contact is achieved, but external quantum efficiency decreases drastically as size decreases below 50 μm
Solution Approach 1:
The patent transitions from conventional vertical mesa structures to a lateral P-N junction configuration where the third region extends in the longitudinal direction bordering the first and second regions. This dimensional reconfiguration enables electrical contacts to be made on a single face while maintaining efficient carrier recombination in the quantum well region, resolving the contradiction between manufacturability and efficiency.
2Ease of manufacture
If flat surface is retained for making contacts on μLEDs to reduce production cost, then production cost decreases, but mutual optical couplings occur between adjacent LEDs when spacing is reduced
Solution Approach 1:
The lateral P-N junction structure inherently segments the optical paths of adjacent LEDs by confining the active recombination region to the lateral junction area. This segmentation prevents optical crosstalk between neighboring pixels, enabling reduced spacing without mutual optical coupling while maintaining flat surface contacts for cost-effective production.
Solution Approach 2:
The patent creates a localized active region at the lateral P-N junction where carrier recombination is concentrated. This local quality enhancement ensures that photons are generated primarily within the defined junction area, preventing stray light from causing mutual optical coupling between adjacent LEDs while maintaining flat surface contacts.
3Ease of manufacture
If flat surface is used for contacts, then production cost is reduced, but carrier recombination in quantum wells is not optimal due to poor electron confinement
Solution Approach 1:
The patent introduces a lateral dimension for the P-N junction configuration, creating a third region that borders the first and second regions in the longitudinal direction. This lateral junction structure provides effective electron confinement to the quantum wells through the built-in electric field at the lateral interface, achieving optimal carrier recombination while maintaining flat surface contacts for cost-effective manufacturing.
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 configuration improves radiative recombination rates, reduces non-radiative recombinations, and prevents mutual optical couplings, leading to higher efficiency and compactness of LEDs, allowing for smaller pixel sizes and reduced spacing without degrading performance.
Implementation Method 1
By polarising the LED, an electron from the N-type region can recombine with a hole from the P-type region. This recombination of carriers (electrons, holes) is said to be radiative if it is accompanied by the emission of a photon.
Implementation Method 2
This lateral P-N junction generates a space charge region (SCR) developing laterally on either side of the junction. The SCR pushes part of the carriers towards a central region of the LED.
Implementation Method 3
Solid-state LEDs can further comprise a quantum well region. These quantum wells are configured to spatially confine carrier recombination and optimise photon emission.
Data Source
AI summary
A light-emitting diode 100 includes a first region 1, for example of the P type, formed in a first layer 10 and forming, in a direction normal to a basal plane, a stack with a second region 2 having at least one quantum well formed in a second layer 20, and including a third region 3, for example of the N type, extending in the direction normal to the plane, bordering and in contact with the first and second regions 1, 2, through the first and second layers 10, 20. A process for producing a light-emitting diode 100 in which the third region 3 is formed by implantation into and through the first and second layers 10, 20.