Multiband Photocathode With Segmented Emission Surfaces
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Solution Overview
Problem
Existing photocathodes have insufficient sensitivity in the visible spectrum and are unable to effectively image the near infrared spectrum, with a high probability of electron recombination or trapping in the first elementary layers, and lack the ability to dynamically switch between spectral bands.
Innovation Solution
A photocathode with a multilayer structure where each elementary layer has its own photoelectric emission surface, formed by interleaved patterns, allowing for optimized sensitivity across the visible and near infrared spectra, and the ability to selectively emit electrons based on spectral band requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a multilayer structure with decreasing band gaps is used to extend sensitivity to near infrared, then spectral range is improved, but sensitivity in visible spectrum deteriorates due to electron recombination and trapping in first layers
Solution Approach 1:
The photocathode is segmented into multiple independent photoelectric emission surfaces, each associated with a specific elementary layer. This segmentation allows each layer to independently contribute to the spectral response without electrons from upper layers being lost to recombination or trapping, thereby maintaining high visible spectrum sensitivity while extending near infrared coverage through the multilayer structure.
Solution Approach 2:
Each elementary layer is given a distinct local quality through its specific band gap energy, optimized for a particular spectral region. The first layer has a larger band gap for visible light, while subsequent layers have progressively smaller band gaps for near infrared. This local optimization of each layer's properties resolves the contradiction by allowing each layer to excel at its designated spectral range without compromising others.
2Adaptability or versatility
If electrons must traverse multiple layers to reach the emission surface, then spectral range is extended, but electron loss through recombination and trapping increases
Solution Approach 1:
The emission surface is segmented to provide direct access from each elementary layer to its own photoelectric emission surface. This segmentation eliminates the need for electrons to traverse multiple layers, thereby preventing recombination and trapping losses while still enabling extended spectral range through the multilayer configuration.
Solution Approach 2:
Each elementary layer is provided with its own dedicated photoelectric emission surface as an intermediary, allowing electrons generated in that layer to be directly emitted without passing through other layers. This intermediary emission surface resolves the contradiction by providing a direct extraction path for electrons from each layer, minimizing losses while maintaining spectral versatility.
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 structured photocathode achieves high quantum efficiency (up to 25%) across the entire spectral range, enabling dynamic switching between visible and near infrared spectral bands, improving image sensitivity and spectral selection capabilities.
Implementation Method 1
incident photons pass through the window layer from the receiving face, and then penetrate the active layer where they generate electron-hole pairs. The generated electrons move to the emitting face of the active layer and are emitted in vacuum.
Data Source
AI summary
The invention relates to a photocathode including an input window (210) suitable for receiving a flow of incident photons, and an active layer (230), the active layer consisting of a plurality of elementary layers (2301, 2302) made of semiconductor materials having decreasing forbidden bandwidths in the direction of the flow of incident photons. The surface of the photocathode opposite the input window is structured so that each elementary layer of the active layer has its own photoelectric emission surface (2401, 2402). By choosing the semiconductor materials of the elementary layers, it is possible to obtain an image which has high sensitivity in both the visible spectrum and the near infrared.