Overdoped Conduction Mesh for Photodetection Stability
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Solution Overview
Problem
Diode array photo-detectors face challenges in sensitivity due to electrical resistance in the substrate, leading to variations in polarization and charge transfer issues, as well as defects at the interface between the passivation layer and semiconductor regions, which reduce photonic signal quality and increase noise.
Innovation Solution
A photo-detection device with a conduction mesh formed by metal diffusion between adjacent diodes, reducing series access resistance and stabilizing the interface, combined with a peripheral substrate contact and a CdHgTe absorption layer with varying gap energy, enhancing charge collection and reducing dark current.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a diode array is used for detection of electromagnetic radiation, then the ability to capture spatio-temporal variation of light intensity is improved, but electrical resistance in the substrate induces variation in polarization and alters diode operation
Solution Approach 1:
The substrate is divided into multiple independently contacted regions, with each diode having its own dedicated substrate contact. This segmentation eliminates the collective RC effect and polarization variations that occur when all diodes share a common substrate contact, as each diode operates electrically independently with its own reference potential.
Solution Approach 2:
Each diode region is provided with localized substrate contacts positioned close to the individual diodes, creating locally optimized electrical pathways. This local quality approach reduces the series resistance and RC time constants for each pixel, improving both detection sensitivity and operational stability compared to peripheral substrate contacts.
2Productivity
If the number of diodes and photon flux are increased, then the detection capability is improved, but the electrical resistance effect strongly influences diode operation and slows down charge transfer
Solution Approach 1:
The substrate contact structure is segmented into multiple independent contacts, one for each diode or small group of diodes. This segmentation reduces the total series resistance in the charge transfer path and eliminates the collective RC effect that limits charge transfer speed in large-format detectors with high photon flux capabilities.
Solution Approach 2:
Substrate contacts are positioned in the plane of the substrate close to each diode, rather than only at peripheral locations. This two-dimensional distribution of contacts reduces the charge transfer distance and resistance, enabling faster charge extraction even as the detector area and diode count increase.
3Ease of manufacture
If interface defects and trap states are present at the passivation layer-semiconductor interface, then manufacturing is simplified, but carrier generation/recombination centers reduce photonic signal and increase thermal current
Solution Approach 1:
Local substrate contacts are positioned close to each diode, creating localized electrical pathways that minimize the influence of extended interface defects and trap states in the passivation layer. This local contact approach reduces the impact of carrier generation and recombination at interface defects on the overall photonic signal quality.
Solution Approach 2:
The substrate contact structure extracts charges locally at each diode region before they can be significantly affected by interface defects and trap states in the passivation layer. This early charge extraction minimizes the interaction between photogenerated carriers and interface defects, reducing thermal current and improving signal quality.
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 solution improves diode array sensitivity by reducing series resistance and noise, stabilizing the interface, and increasing the modulation transfer function, particularly effective in high flux and low pitch imaging applications.
Implementation Method 1
a heat treatment is performed which causes metal to diffuse into the absorption layer from the metal layer
Implementation Method 2
a heat treatment is performed which causes metal to diffuse into the absorption layer from the metal layer and form an overdoped region under each trench
Implementation Method 3
A diode array can be used to provide detection of electromagnetic radiation. It can indeed form electron-hole pairs by interaction between the electromagnetic radiation and the substrate
Data Source
Figure 1a~2
Figure 3a~3b
Figure 4a~4b
AI summary
The invention relates to a photodetection device comprising a substrate and an array of diodes, the substrate including an absorption layer (1) having a first type of doping, and each diode comprising, in the absorption layer (2), a collection region which has a second type of doping opposite to the first type. The device comprises, under the surface of the substrate, a conductive mesh (7) including at least one conductive channel inserted between the collection regions (2) of two adjacent diodes, the at least one conductive channel (7) having the first type of doping and a higher doping density than the absorption layer. The doping density of the at least one conductive channel (7) is the result of a diffusion of metal in the absorption layer from a metal mesh provided on the surface of the substrate. The invention also relates to a method for manufacturing such a device.