Graded-Shell Quantum Dots for Lattice Mismatch

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Solution Overview

Problem

InP/ZnS-based quantum dots experience lattice mismatch and non-uniform shell epitaxial growth due to differences in lattice constants, leading to wide half-width characteristics and optical instability.

Innovation Solution

A graded multishell structure is introduced with inter shells having stepwise concentration changes from the core to the outer shell, formed through a graded heating-up growth process to minimize lattice and thermal expansion coefficient mismatches, comprising multilayer structures like ZnaSeb/ZncSed/ZneSef and ZngSehSi/ZnjSekSl, optimizing the composition ratios to align energy band-gaps and reduce lattice mismatch.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If ZnS shells are formed around InP core, then quantum confinement is enhanced, but lattice mismatch occurs due to lattice constant difference

Engineering Contradiction:

Improvequantum confinementVSAvoidlattice mismatch

Core Design Contradiction:

ReliabilityVSManufacturing precision

Solution Approach 1:

The patent introduces inter shells with graded composition (InP1-xGaxP and InP1-yGayS) as intermediary layers between the InP core and ZnS outer shell. These intermediate layers serve as a transition zone that gradually bridges the lattice constant difference, preventing direct lattice mismatch while maintaining quantum confinement effects.

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The patent employs continuous variation of compositional parameters (x and y in InP1-xGaxP and InP1-yGayS) and lattice constant parameters across the shell structure. By gradually changing the Ga content and S content from the core outward, the lattice constant transitions smoothly, eliminating abrupt mismatches while preserving the quantum confinement necessary for optical performance.

Inventive Principle:

Principle #35Parameter changes

2Ease of manufacture

If uniform shell structure is used, then fabrication is simplified, but shell epitaxial growth becomes non-uniform due to lattice mismatch

Engineering Contradiction:

Improvefabrication simplicityVSAvoidshell epitaxial growth uniformity

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The patent applies different compositional qualities at different radial positions within the shell structure. The inner region (inter shells) has graded InP-GaP-InP-GaPS composition to accommodate lattice transitions, while the outer region has uniform ZnS composition for stable epitaxial growth. This localized differentiation of material quality enables both simplified overall fabrication and uniform local epitaxial growth.

Inventive Principle:

Principle #3Local quality

3Device complexity

If core and shell materials are directly combined, then device complexity is reduced, but optical characteristics deteriorate due to wide half-width

Engineering Contradiction:

Improvestructure simplicityVSAvoidoptical characteristics

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The patent segments the shell structure into multiple functional zones: inner inter shells with graded InP-GaP composition, middle inter shells with graded InP-GaPS composition, and outer ZnS shell. This segmentation allows each zone to perform its specific function (lattice transition, composition gradient management, protective capping) while collectively maintaining simple overall device architecture and excellent optical characteristics with narrow half-width.

Inventive Principle:

Principle #1Segmentation

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 graded structure enhances quantum confinement and optical characteristics by reducing lattice mismatch and thermal expansion coefficient mismatch, resulting in improved quantum yield and reduced half-width, as seen in red- and green-emitting quantum dots.

Implementation Method 1

lattice mismatch may occur due to a lattice constant difference between the InP core and the ZnS shells

Methodology Applied

Scientific EffectLattice mismatch:

Implementation Method 2

formed through a graded heating-up growth process to minimize thermal expansion coefficient (TEC) mismatch

Methodology Applied

Scientific EffectThermal expansion coefficient mismatch: Thermal Expansion

Implementation Method 3

maximize quantum confinement

Methodology Applied

Scientific EffectQuantum confinement:

Data Source

PatentUS11932794B2Quantum-dot based on graded-shell structure and manufacturing method of the same

Publication Date: 2024.03.19 INDUSTRY UNIVERSITY COOPERATION FOUNDATION HANYANG UNIVERSITY

AI summary

Disclosed are quantum dots based on a graded multishell structure and a method of manufacturing the same. More particularly, each of the quantum dots according to an embodiment of the present invention includes a core, inter shells surrounding the core, and an outer shell surrounding the inter shells, wherein the concentrations of compounds composing the inter shells are changed stepwise from the core to the outer shell.