HgCdTe Avalanche Photodiode with Segmented Doping for Reduced Response Time
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Solution Overview
Problem
Avalanche photodiodes made from mercury-cadmium telluride (CdHg1-xTe) struggle to vary the forbidden band width in the absorption zone, limiting the reduction of response time due to cadmium and mercury interdiffusion during activation annealing, which results in a constant cadmium proportion and thus a fixed response time.
Innovation Solution
A semiconductor structure with a first absorption zone of mercury-cadmium telluride where the cadmium proportion is varied along one dimension, incorporating a doping element like arsenic, which alternates in concentration to prevent cadmium diffusion during annealing, allowing for a varying cadmium proportion and an accelerated carrier diffusion, thereby reducing the response time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a doping element like arsenic is introduced to provide majority carriers in the first zone, then the conductivity is improved, but cadmium and mercury interdiffuse during activation annealing, resulting in a constant cadmium proportion and fixed response time
Solution Approach 1:
The first zone is divided into multiple subzones along the direction of carrier diffusion, where each subzone has a different doping element concentration. This segmentation allows the structure to prevent cadmium diffusion while maintaining conductivity and enabling variable response times through different cadmium proportions in different subzones.
Solution Approach 2:
Different regions of the first zone are assigned different doping element concentrations to achieve local optimization. The doping concentration varies from one subzone to another, creating local variations in carrier concentration that prevent harmful interdiffusion while maintaining overall conductivity and enabling tailored response characteristics.
2Ease of manufacture
If the cadmium proportion is kept constant to maintain structural stability, then manufacturing is simplified, but the response time cannot be reduced
Solution Approach 1:
The cadmium proportion parameter is varied across different subzones of the first zone rather than being kept constant. This parameter change enables the structure to achieve faster response times in certain regions while maintaining overall manufacturing feasibility through a systematic approach to composition control.
3Loss of time
If the cadmium proportion is varied to reduce response time, then the carrier diffusion is accelerated, but cadmium and mercury interdiffusion occurs during annealing
Solution Approach 1:
The doping elements are introduced in a predetermined concentration distribution before the activation annealing process. This preliminary action creates a concentration gradient that acts as a barrier to cadmium diffusion during subsequent thermal processing, allowing the structure to maintain its varied cadmium proportion and achieve reduced response time without composition degradation.
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 structure achieves a reduced response time by varying the cadmium proportion, enhancing the electric field for faster carrier diffusion and improving the signal-to-noise ratio without significant cadmium diffusion risks, outperforming conventional configurations.
Implementation Method 1
a first so-called absorption semiconductor zone of a first type of conductivity having a first longitudinal face intended to receive the electromagnetic radiation
Implementation Method 2
the second zone being adapted to provide a multiplication of carriers by ionization by impact
Implementation Method 3
the concentration of which is varied alternately in a direction substantially perpendicular to the first longitudinal face between a so-called low concentration and a so-called high concentration
Data Source
Figure 1~2
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AI summary
The invention relates to a semiconductor structure (1) of the avalanche photodiode type intended to receive electromagnetic radiation in a given wavelength range. The structure comprises a first semiconductor zone (210) of a first type of conductivity having a first longitudinal face (201), said first zone (210) being made of mercury-cadmium telluride of the type CdxHg1-xTe with a varying proportion x of cadmium. The structure (1) further comprises at least one second semiconductor zone (310) in contact with the first zone (210), and a third semiconductor zone (410) in contact with the second zone (310). The first zone (210) comprises a dopant element, such as arsenic, the concentration of which is varied alternately in a direction substantially perpendicular to the first longitudinal face (201) between a so-called low concentration and a so-called high concentration.The invention further relates to a method of manufacturing a structure (1) according to the invention.