Spin-Polarized Electron Source Intermediate Layer Strain Engineering

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Solution Overview

Problem

Spin-polarized electron generating devices using strained superlattice layers face challenges in achieving high spin polarization and external quantum efficiency due to dislocations caused by strain accumulation and lattice mismatch between the buffer layer and substrate, leading to reduced polarization and quantum efficiency.

Innovation Solution

Incorporating an intermediate layer with a lattice constant greater than the buffer layer to impose tensile strain on the buffer layer, which reduces dislocation density and improves crystallinity, allowing for higher spin polarization and quantum efficiency regardless of substrate material selection.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Measurement precision

If a strained superlattice layer is used to achieve high spin polarization, then spin polarization is improved, but dislocations occur due to strain accumulation and lattice mismatch, reducing quantum efficiency

Engineering Contradiction:

Improvespin polarizationVSAvoidquantum efficiency

Core Design Contradiction:

Measurement precisionVSReliability

Solution Approach 1:

An intermediate layer with lattice constant greater than the buffer layer is introduced between the substrate and the strained superlattice layer. This intermediate layer acts as a mediator that imposes tensile strain on the buffer layer, reducing dislocation density and improving crystallinity of the strained superlattice layer, thereby maintaining both high spin polarization and quantum efficiency

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The invention changes the lattice constant parameter by selecting an intermediate layer material with a larger lattice constant than the buffer layer. This parameter change induces tensile strain in the buffer layer, which counteracts the compressive strain from the strained superlattice layer, reducing dislocation formation and improving overall device performance

Inventive Principle:

Principle #35Parameter changes

2Device complexity

If the buffer layer is directly formed on the substrate, then device structure is simplified, but lattice mismatch causes dislocations that reduce spin polarization and quantum efficiency

Engineering Contradiction:

Improvelayer structureVSAvoidspin polarization

Core Design Contradiction:

Device complexityVSMeasurement precision

Solution Approach 1:

The intermediate layer serves as an intermediary component between the substrate and buffer layer, specifically designed to have a lattice constant greater than the buffer layer. This intermediary structure resolves the lattice mismatch issue without significantly complicating the overall device structure, maintaining spin polarization through reduced dislocation density

Inventive Principle:

Principle #24Intermediary (Mediator)

3Reliability

If tensile strain is imposed on the buffer layer to reduce dislocation density, then crystallinity is improved, but additional layer complexity is introduced

Engineering Contradiction:

ImprovecrystallinityVSAvoidlayer structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The intermediate layer is positioned between the substrate and buffer layer to impose tensile strain on the buffer layer. This strain imposition improves the crystallinity of the strained superlattice layer by reducing dislocation density, while the intermediate layer itself remains a simple single-layer structure that does not significantly increase device complexity

Inventive Principle:

Principle #24Intermediary (Mediator)

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 intermediate layer effectively separates valence bands, reducing spin-flip scattering and enhancing external quantum efficiency, resulting in improved spin polarization and quantum efficiency of the electron beam.

Implementation Method 1

Incorporating an intermediate layer with a lattice constant greater than the buffer layer to impose tensile strain on the buffer layer, which reduces dislocation density and improves crystallinity

Methodology Applied

Scientific EffectStrain: Deformation

Implementation Method 2

Through additive utilization of the strain and an effect yielded by quantum confinement, further band splitting is implemented

Methodology Applied

Scientific EffectBand splitting:

Implementation Method 3

Through additive utilization of the strain and an effect yielded by quantum confinement, further band splitting is implemented

Methodology Applied

Scientific EffectQuantum confinement:

Implementation Method 4

Circularly polarized light with which the semiconductor photocathode is irradiated excites electrons from a heavy-hole band and a light-hole band to a conduction band

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Data Source

PatentUS8344354B2Spin-polarized electron source

Publication Date: 2013.01.01 NAT UNIV CORP TOKAI NAT HIGHER EDUCATION & RES SYST

AI summary

A spin-polarized electron generating device includes a substrate, a buffer layer, a strained superlattice layer formed on the buffer layer, and an intermediate layer formed of a crystal having a lattice constant greater than a lattice constant of a crystal of the buffer layer, the intermediate layer intervening between the substrate and the buffer layer. The buffer layer includes cracks formed in a direction perpendicular to the substrate by tensile strain.