Avalanche Photodiode Edge Termination for UV Signal Uniformity
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Solution Overview
Problem
Avalanche photodiodes for detecting ultraviolet photons suffer from degraded stability, sensitivity, and uniformity due to charge carrier generation at the device edges, leading to nonuniform and unreliable signal responses, especially when detecting low-level radiation.
Innovation Solution
The photodiode design ensures avalanche multiplication occurs in the bulk active region by laterally extending the edge termination outside the surface, achieving an electric field strength equal to the critical field strength at the pn-junction, thereby eliminating edge influences on the signal. This is achieved by reducing the effective surface charge density in steps, with specific doping and thickness configurations in the fourth layer to control the electric field and ensure total depletion of the second layer at low voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the edge termination is not extended laterally outside the surface, then the device structure is simpler, but charge carrier generation occurs at the device edges resulting in nonuniform signal and degraded stability
Solution Approach 1:
The edge termination is extended laterally outside the surface in the horizontal dimension, separating it from the bulk active region. This spatial separation in another dimension prevents edge effects from contaminating the detection signal while maintaining overall device functionality.
Solution Approach 2:
The device is segmented into distinct regions: the bulk active region for photon detection and the laterally extended edge termination region. This segmentation isolates the edge effects to a separate spatial zone, preventing them from affecting the uniformity and stability of signals generated in the bulk active region.
2Measurement precision
If the reverse bias is increased above the breakdown voltage for Geiger mode operation, then the sensitivity for detecting very low radiation levels is improved, but the edge effects become more pronounced causing nonuniform signal
Solution Approach 1:
The harmful edge effects are extracted and isolated to the laterally extended termination region, removing their influence from the bulk active region where photon detection occurs. This allows Geiger mode operation with high sensitivity while maintaining signal uniformity.
Solution Approach 2:
The laterally extended edge termination acts as an intermediary structure that manages the high electric field conditions required for Geiger mode operation, confining the associated edge effects to itself while protecting the bulk active region from these detrimental influences.
3Manufacturing precision
If the surface charge density is not controlled, then the manufacturing process is simpler, but the electric field distribution becomes nonuniform causing edge contributions to the signal
Solution Approach 1:
Different regions of the device are given different surface charge densities optimized for their specific functions. The bulk active region maintains uniform charge for consistent photon detection, while the laterally extended edge termination has controlled charge distribution to manage edge effects, achieving local optimization of electric field characteristics.
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 enhances the sensitivity and stability of the photodiode by ensuring that the signal is free from edge contributions, allowing for reliable detection of low-level ultraviolet radiation with improved uniformity and reproducibility.
Implementation Method 1
When radiation enters an avalanche photodiode reverse biased so as to have an active region with a high electric field for avalanche multiplication of charge carriers created therein, a chain-reaction concerning generation of electron-hole pairs will result in the diode. This avalanche multiplication of the photo current results in an amplified signal of the diode
Implementation Method 2
The detection of UV-radiation is useful for a wide range of civil and military applications... When radiation enters an avalanche photodiode reverse biased so as to have an active region with a high electric field for avalanche multiplication of charge carriers created therein
Data Source
Figure 1~6
Figure 2~4
Figure 7~8
AI summary
An avalanche photodiode for detecting ultraviolet photons comprises a first semiconductor layer (1) and a low doped second semiconductor layer (2) on top thereof. These layers are of SiC or Al x Ga 1-x N, in which 0 ‰¤ x ‰¤ 0.5, and x may be different for these layers of the diode. A voltage close to the breakdown voltage of the diode being intended to be applied across electrodes (6, 7) of the diode in operation thereof for creating an active region of a high electric field for avalanche multiplication of charge carriers created by said photons in said second layer. A fourth layer (9) is arranged above the second layer laterally outside a surface (4) of the diode being configured to be exposed to photons to be detected, with the second (7) of said electrodes arranged on top thereof. The thickness of the fourth layer (9) and the doping concentration thereof are adapted to obtain an effective surface charge density of said fourth layer in a region laterally next to said surface obtaining an electric field strength substantially equal to a critical electric field strength of the diode at a pn-junction formed below said fourth layer laterally to said surface upon application of a said voltage across said electrodes.