Semiconductor Photocathode Tip With Electric-Field Electron Affinity Control

Solution Overview

Problem

Existing electron emitters, particularly tungsten-filament-based and semiconductor-based emitters, are not well-suited for non-continuous emission modes and require periodic surface reactivation, leading to inefficiencies and increased complexity due to caesium coating degradation.

Innovation Solution

A semiconductor-based electron emitter with a p-type doped tip geometry and controlled electric field application, utilizing the lightning rod effect to enhance electron emission efficiency without the need for caesium coating, allowing for precise control of electron affinity and emission through laser-induced photoemission.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Productivity

If a caesium coating is applied to lower electron affinity, then photoelectron emission efficiency is improved, but the coating degrades during operation requiring periodic reactivation and increasing device complexity

Engineering Contradiction:

Improvephotoelectron emission efficiencyVSAvoidcomplexity of in-situ recoating mechanism

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent removes the caesium coating layer entirely from the semiconductor photocathode surface. Instead of using external caesium coating and reactivation mechanisms, the invention uses the semiconductor's intrinsic properties (bandgap engineering and electric field control) to achieve and maintain negative electron affinity without any coating that would degrade over time.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The semiconductor photocathode structure is designed to self-maintain negative electron affinity through its intrinsic band structure and applied electric field. The system does not require external reactivation or recoating operations because the negative electron affinity state is stable and self-sustaining as long as the electric field is applied, eliminating the need for complex maintenance mechanisms.

Inventive Principle:

Principle #25Self-service

2Productivity

If a caesium coating is applied to lower electron affinity, then photoelectron emission efficiency is improved, but operational lifetime is reduced due to coating degradation

Engineering Contradiction:

Improvephotoelectron emission efficiencyVSAvoidoperational lifetime of emitter

Core Design Contradiction:

ProductivityVSDuration of action of stationary object

Solution Approach 1:

The patent removes the caesium coating layer entirely from the semiconductor photocathode surface. Instead of using external caesium coating and reactivation mechanisms, the invention uses the semiconductor's intrinsic properties (bandgap engineering and electric field control) to achieve and maintain negative electron affinity without any coating that would degrade over time.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The invention replaces the expensive, short-living caesium coating (which requires periodic replacement) with a stable, long-living semiconductor structure. The semiconductor photocathode maintains its electron affinity properties indefinitely without degradation, as long as the applied electric field is maintained, eliminating the need for periodic recoating operations.

Inventive Principle:

Principle #27Cheap short-living objects (Disposable)

3Reliability

If laser power is constantly adjusted to account for caesium degradation, then electron beam current is maintained, but device complexity and operational cost increase

Engineering Contradiction:

Improveelectron beam current stabilityVSAvoidcomplexity of power adjustment mechanism

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The semiconductor photocathode structure is designed to self-maintain negative electron affinity through its intrinsic band structure and applied electric field. The system does not require external reactivation or recoating operations because the negative electron affinity state is stable and self-sustaining as long as the electric field is applied, eliminating the need for complex maintenance mechanisms.

Inventive Principle:

Principle #25Self-service

Solution Approach 2:

The invention changes the fundamental parameter of electron affinity control from external coating-based (caesium) to intrinsic semiconductor-based (bandgap engineering). This parameter change enables stable, long-term operation without the need for continuous adjustment or reactivation, as the semiconductor's electronic properties are inherently stable under operating conditions.

Inventive Principle:

Principle #35Parameter changes

4Productivity

If in-situ recoating mechanism is included to maintain caesium coating, then emission efficiency is maintained, but device size, cost, and complexity increase

Engineering Contradiction:

Improveemission efficiency maintenanceVSAvoidelaborate mechanism for caesium recoating

Core Design Contradiction:

ProductivityVSDevice complexity

Solution Approach 1:

The patent removes the caesium coating layer entirely from the semiconductor photocathode surface. Instead of using external caesium coating and reactivation mechanisms, the invention uses the semiconductor's intrinsic properties (bandgap engineering and electric field control) to achieve and maintain negative electron affinity without any coating that would degrade over time.

Inventive Principle:

Principle #2Taking out (Extraction)

Solution Approach 2:

The semiconductor photocathode structure performs multiple functions: it provides the photoexcitation function, maintains negative electron affinity, and ensures long-term stability—all through its intrinsic properties. This eliminates the need for separate coating and reactivation subsystems, as the semiconductor material itself fulfills all necessary functions.

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

Enables efficient, high-yield electron emission in both continuous and pulsed modes without surface activation, reducing the complexity and cost of the emitter design and extending its operational lifetime.

Implementation Method 1

a laser beam 110 illuminating the back of the plate causes photons to impact on the back of plate 110, to thereby cause electron emission from the front of the plate

Methodology Applied

Scientific EffectPhotoelectric effect: Photoelectric Effect

Implementation Method 2

the graded affinity structure promotes the attraction of electrons from the substrate to the surface via the bending of the conduction band of the graded affinity structure downward

Methodology Applied

Scientific EffectBand bending:

Implementation Method 3

a new electron source is needed... utilizing the lightning rod effect to enhance electron emission efficiency without the need for caesium coating, allowing for precise control of electron affinity

Methodology Applied

Scientific EffectElectric field control: Electric Field

Data Source

PatentUS20240412938A1Semiconducting cold photocathode device using electric field to control the electron affinity

Publication Date: 2024.12.12 ATTOLIGHT AG

AI summary

An electron emitter comprises a tapered-shaped emission tip having a base face and an apex opposite the base face, the emission tip consisting essentially of semiconductor material, the semiconductor material being partially doped n-type and partially doped p-type, wherein the base face is doped one of n-type or p-type and the apex is doped opposite type of the base face and a p-n junction is thereby formed at a position between the base face and the apex.