Photodiode Field Electrode Space Charge Reduction
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Solution Overview
Problem
Existing photodiode devices face challenges in minimizing dark current interference, which affects the accuracy of photocurrent measurements.
Innovation Solution
The photodiode device incorporates a substrate with doped regions of opposite conductivity types, a contact region at the surface, and a field electrode separated by dielectric material, allowing for voltage application to reduce the lateral dimension of the space charge region, thereby minimizing dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a bias voltage is applied to increase the extension of the space charge region, then the electric field strength is improved, but the dark current increases due to charge carriers generated at crystalline defects near the substrate surface
Solution Approach 1:
The patent extracts the harmful effect by removing charge carriers generated at crystalline defects from the measurement circuit. This is achieved by forming a lateral pn junction that creates a separate collection path for these carriers, directing them away from the main measurement path and into a drain region, thereby eliminating their contribution to dark current while maintaining the necessary electric field strength
Solution Approach 2:
The patent segments the charge carrier collection paths by creating distinct regions: a main collection path for signal carriers and a separate drain path for dark current carriers. The lateral pn junction divides the semiconductor structure into regions with different functions, allowing simultaneous optimization of both signal detection and dark current reduction
2Power
If the space charge region is extended by reverse bias voltage, then the photocurrent generation is improved, but the measurement precision deteriorates due to interference from dark current
Solution Approach 1:
The patent extracts the harmful dark current component from the measurement path by routing it through a separate collection path created by the lateral pn junction. This separation allows the main measurement circuit to receive only the photocurrent signal, significantly improving measurement precision while maintaining effective photocurrent generation in the extended space charge region
Solution Approach 2:
The lateral pn junction acts as an intermediary structure that mediates between the space charge region and the external circuit. It provides a controlled interface that selectively directs different types of charge carriers to different destinations, enabling the system to maintain high photocurrent generation while achieving precise measurement by filtering out dark current interference
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 configuration significantly reduces dark current by shrinking the space charge region and pinching it at the diode periphery, enhancing the accuracy of photocurrent measurements.
Implementation Method 1
A field electrode is arranged above the lateral pn junction and is separated from the lateral pn junction by a dielectric material, and the field electrode is provided with a further electrical connection separate from the anode and cathode connections
Implementation Method 2
When the photodiode is irradiated, electron-hole pairs are produced in the crystalline semiconductor material by lifting electrons from the valence band up into the conduction band
Implementation Method 3
A field electrode is arranged above the lateral pn junction and is separated from the lateral pn junction by a dielectric material
Data Source
Figure 1~2
Figure 3
Figure 4
AI summary
The photodiode device comprises a doped region (2) contiguous with a contact region (3) of the same conductivity type located at the substrate surface (1'), an appertaining anode or cathode connection (7, 11), a further contact region (5) of an opposite conductivity type at the substrate surface, and a further anode or cathode connection (8, 12). The contact region (3) is arranged at least on opposite sides of an active area of the substrate surface that covers the further contact region (5). A lateral pn junction (16) and an associated space charge region is formed at the substrate surface by a boundary of one of the contact regions, the boundary facing the other contact region. A field electrode (6) is arranged above the lateral pn junction, separated from the lateral pn junction by a dielectric material (10), and is provided with a further electrical connection (9, 13) separate from the anode and cathode connections. By the field electrode (6), the space charge region at the surface (1') is reduced and the peripheral dark current of the photodiode decreases considerably.