Bispectral Detector Recess Masking for Recombination Noise
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Solution Overview
Problem
Bispectral detectors with semiconductor layers face issues due to imperfections in recesses, leading to high recombination rates and noise, which degrade the quality of detection and reduce fill factor.
Innovation Solution
A bispectral detector design where recesses in the upper layer are electrically masked by a doping screen layer with a high concentration of dopants, preventing charge carriers from recombining on imperfections and reducing crosstalk, achieved through ion implantation and appropriate layer thickness to ensure minority carriers do not reach the recess sides.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If recesses are machined through the top layer to access the lower layer for forming PN junctions, then photodiode formation is enabled, but recombination occurs on the imperfect recess walls reducing detection quality
Solution Approach 1:
A screen layer of opposite conductivity type is introduced as an intermediary between the recess walls and the charge carriers. This screen layer acts as a mediator that prevents direct interaction between carriers and the harmful recess walls, thereby reducing recombination while maintaining the necessary structural access through recesses.
Solution Approach 2:
The imperfect recess walls, which originally cause harmful recombination, are transformed into a beneficial structure by coating them with a screen layer of opposite conductivity type. This converts the harmful surface into a protective barrier that actually reduces recombination by repelling carriers away from the defective walls.
2Productivity
If the fill factor of photodiodes is increased by optimizing recess geometry, then detection efficiency improves, but recombination on recess walls increases
Solution Approach 1:
The screen layer serves as a protective intermediary that allows the recess geometry to be optimized for high fill factor without suffering from the accompanying recombination losses. It decouples the geometric optimization from the electrical performance degradation.
3Reliability
If charge carriers are collected efficiently from both layers, then detection sensitivity improves, but crosstalk between layers occurs
Solution Approach 1:
The screen layer acts as an electrical intermediary that prevents direct carrier exchange between the two active layers. By introducing this intermediate conductivity layer, carriers can be collected efficiently from each layer while the screen layer blocks the crosstalk pathway.
Solution Approach 2:
The detector structure is segmented into distinct electrical zones separated by the screen layer. This segmentation creates independent collection regions for each layer while maintaining physical proximity for efficient carrier collection, thereby reducing inter-layer crosstalk.
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 approach significantly reduces recombination sources and noise, optimizing the fill rate of photodiodes and minimizing crosstalk, thereby enhancing the detector's performance and quality.
Implementation Method 1
A doping screen layer with a high concentration of dopants, which masks said recesses electrically for said charge carriers, is formed on said recesses on which said semiconductor zones of the second type are formed
Implementation Method 2
separated by an intermediate layer forming a potential barrier between the upper and lower layers
Implementation Method 3
a stack of upper and lower semiconductor layers of a first type of conductivity for the absorption of the first and second ranges of electromagnetic radiation respectively
Implementation Method 4
absorption of incident radiation
Data Source
Figure 1
Figure 2~5
Figure 4~6
AI summary
The bispectral detector comprises a stack of upper and lower semiconductor layers of a first conductivity type for the absorption of first and second ranges of electromagnetic radiation, semiconductor areas of a second conductivity type that is opposite to first type, and electrically conducting elements connected to semiconductor areas for the collection of electric charges. The upper and lower semiconductor layers are separated by an intermediate layer that forms a barrier of potential between the upper (18) and lower layers (14). The bispectral detector comprises a stack of upper and lower semiconductor layers of a first conductivity type for the absorption of first and second ranges of electromagnetic radiation, semiconductor areas of a second conductivity type that is opposite to first type, and electrically conducting elements connected to semiconductor areas for the collection of electric charges. The upper and lower semiconductor layers are separated by an intermediate layer that forms a barrier of potential between the upper (18) and lower layers (14). Each semiconductor area in the lower layer is implanted partially in a bottom of recesses traversing the upper layer and an intermediate layer (16). The recess traversing the upper layer is separated from the upper layer by a second semiconductor barrier layer of a second conductivity type. A concentration of dopants of the second conductivity is greater than 10 1> 7>cm -> 3>. A thickness is chosen according to the concentration and is greater than a length of diffusion of the minority charge carrier in the barrier layer. Each semiconductor area in the upper layer forms a continuous volume with an adjacent semiconductor area in the lower layer. The intermediate layer is made of an insulating material or a semiconductor material of the first conductivity type of which a band gap is greater than three times of each of the upper and lower layers. An independent claim is included for a process for manufacturing a bispectral detector.