Quantum Dot Color Conversion in Micro-LED Optical Cavities

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Solution Overview

Problem

III-nitride light emitting diodes (LEDs) with high indium content suffer from efficiency and uniformity issues due to indium doping challenges, especially at smaller sizes, which affects the emission of longer wavelengths like red light, leading to degraded performance in display devices such as augmented reality displays.

Innovation Solution

Employing undoped GaN or low indium doped GaN active regions coupled with photonically pumped quantum dots in a vertical cavity structure, which absorb and convert ultraviolet or blue photons into various colors, avoiding indium doping issues and enhancing efficiency and uniformity.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Length of stationary object

If high indium content is used in III-nitride LEDs to achieve longer wavelength emission, then the emission wavelength increases, but efficiency and uniformity deteriorate due to indium doping challenges

Engineering Contradiction:

Improveemission wavelengthVSAvoidefficiency and uniformity

Core Design Contradiction:

Length of stationary objectVSReliability

Solution Approach 1:

The device is segmented into two functional parts: a blue/UV LED emitting region and a quantum dot color conversion layer. The LED emits at a shorter wavelength (450-480nm) where III-nitride materials perform reliably, while the quantum dots convert this light to longer wavelengths (red, green, yellow) that would otherwise require problematic high-indium-content materials. This segmentation allows each component to operate in its optimal performance range.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Quantum dots serve as an intermediary medium between the blue/UV LED and the final visible output. Instead of directly emitting longer wavelengths through high-indium-content active regions, the system uses quantum dots to absorb blue/UV photons and re-emit at the desired longer wavelengths. This intermediary approach avoids the doping challenges of high-indium III-nitride while achieving the same spectral output.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Length of stationary object

If indium doping is increased to emit red light, then the emission wavelength shifts to red, but performance degrades due to doping challenges at smaller sizes

Engineering Contradiction:

Improveemission wavelengthVSAvoiduniformity

Core Design Contradiction:

Length of stationary objectVSManufacturing precision

Solution Approach 1:

The system changes the controlling parameter for wavelength selection from indium composition (which has poor precision control) to quantum dot size (which can be precisely controlled during synthesis). Quantum dots of different sizes emit at different wavelengths according to quantum confinement effects, allowing precise wavelength control without relying on difficult indium doping processes. This enables uniform red, green, and yellow emission across small pixel pitches.

Inventive Principle:

Principle #35Parameter changes

3Reliability

If quantum dots are used to convert photons, then color efficiency and uniformity improve, but device complexity increases due to additional layers and structures

Engineering Contradiction:

Improvecolor emission uniformityVSAvoidcavity structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The quantum dot layer serves multiple functions simultaneously: it converts blue/UV light to longer wavelengths, acts as an optical cavity filler to enhance light extraction, and provides a platform for precise wavelength control through size tuning. The vertical cavity structure serves both as a mechanical support and as an optical resonator that enhances the interaction between light and quantum dots, improving conversion efficiency while maintaining a relatively simple overall structure.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 improves the efficiency and uniformity of color emission across micro-LED arrays by using quantum dots to convert photons, ensuring high quantum efficiency and purity of color, even at smaller pixel pitches and sizes, while maintaining high optical extraction and preventing photon loss.

Implementation Method 1

quantum dots in a vertical cavity structure, which absorb and convert ultraviolet or blue photons into various colors

Methodology Applied

Scientific EffectPhotoluminescence: Photoluminescence

Implementation Method 2

an optical cavity formed by lateral cavity walls that extend from a substrate to above a light emitting diode

Methodology Applied

Scientific EffectTotal internal reflection: Total Internal Reflection

Data Source

PatentUS20230155075A1Light emitting devices including a quantum dot color conversion material and method of making thereof

Publication Date: 2023.05.18 SHOEI CHEM IND CO LTD

AI summary

A light emitting device includes a first optical cavity bounded by cavity walls, a first light emitting diode located in the first optical cavity and configured to emit blue or ultraviolet radiation first incident photons, a first color conversion material located over the first light emitting diode and configured to absorb the first incident photons emitted by the light emitting diode and to generate first converted photons having a longer peak wavelength than a peak wavelength of the first incident photons, and a first color selector located over the first color conversion material and configured to absorb or reflect the first incident photons and to transmit the first converted photons.