Lateral Single-Photon Avalanche Diode for Low-Voltage NIR Detection
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Solution Overview
Problem
Conventional single-photon avalanche diodes require high breakdown voltages to achieve a wide space charge region for efficient near-infrared radiation detection, limiting the absorption of radiation at wavelengths like 800 nm to about 10% due to a restricted space charge region dimension.
Innovation Solution
A lateral single-photon avalanche diode design featuring a semiconductor body with epitaxial layers and a trench filled with doped polysilicon, allowing for a low breakdown voltage and deep absorption region, with the pn-junction formed between the doped region and the epitaxial layers, enabling efficient radiation detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If the breakdown voltage is increased to achieve a wide space charge region, then the absorption of near-infrared radiation is improved, but the operating voltage exceeds the preferred range of 20 V to 40 V
Solution Approach 1:
The patent transitions from a conventional vertical pn-junction geometry to a lateral pn-junction geometry where the junction extends horizontally through epitaxial layers. This dimensional change allows the space charge region to extend deeper into the semiconductor body without requiring increased breakdown voltage, as the electric field distribution is redistributed across the lateral structure rather than being confined to a vertical depletion region.
Solution Approach 2:
The patent employs selective doping in different regions: the first epitaxial layer has higher doping concentration (10^17 to 10^18 atoms/cm³) while the second epitaxial layer has lower or intrinsic doping. This local variation in doping quality creates optimal conditions for maintaining low breakdown voltage in the avalanche region while enabling deep radiation absorption through the lightly-doped second layer.
2Measurement precision
If the space charge region dimension is increased to improve radiation absorption, then the quantum efficiency is improved, but the breakdown voltage must be increased beyond preferred operating ranges
Solution Approach 1:
By configuring the pn-junction laterally with the p-type doped region extending through multiple epitaxial layers, the space charge region achieves greater effective path length for photon interaction without increasing the vertical depletion width that would require higher breakdown voltages. The lateral extension provides extended interaction volume while maintaining controlled electric field strength.
Solution Approach 2:
The patent uses a composite structure of differently doped epitaxial layers (first layer with higher doping, second layer with lower or intrinsic doping) to create regions with different functional properties. The heavily-doped first layer provides structural support and controlled breakdown characteristics, while the lightly-doped second layer enables deep photon absorption with minimal additional voltage requirement.
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 design enhances quantum efficiency and absorption of long wavelengths (>670 nm) while maintaining a low breakdown voltage, ensuring effective Geiger-mode operation with improved dynamic efficiency and reduced crosstalk in pixel arrays.
Implementation Method 1
The first further layer is a first epitaxial layer grown on the base layer, and the second further layer is a second epitaxial layer grown on the first further layer
Implementation Method 2
Avalanche photodiodes having the pn junction biased in the reverse direction become conducting when the applied voltage exceeds a breakdown voltage. In this mode of operation the electric field strength in the space charge region can attain values of more than 500 kV/cm, so that already few electron-hole pairs generated by incident photons can trigger a self-sustaining avalanche current
Implementation Method 3
A doped region of a second type of conductivity, which is opposite to the first type of conductivity, is arranged in the semiconductor body, penetrates the first further layer and extends into the base layer and into the second further layer
Data Source
Figure 1~2
Figure 3
AI summary
A lateral single-photon avalanche diode comprises a semiconductor body (1) of a first type of conductivity which includes a base layer (10), a first further layer (11) on the base layer and a second further layer (12) on the first further layer. The base layer and the second further layer have an intrinsic doping or a doping concentration that is lower than the doping concentration of the first further layer. Thereby, the high electric field region or avalanche region is essentially confined to the first further layer (11). A doped region (5) of an opposite second type of conductivity is arranged in the semiconductor body, penetrates the first further layer and extends into the base layer and into the second further layer. Anode and cathode terminals (3, 4) are electrically connected to the first further layer and the doped region, respectively. The doped region can be produced by filling a trench (19) with doped polysilicon.