Infrared Photodetector Anti-Reflection Stack for Shorter Fall Time
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Solution Overview
Problem
Existing semiconductor light receiving devices have complex structures and high manufacturing costs due to the need for multiple light-absorption layers, which increase the fall time and create a 'dead zone' in detecting defects in optical fiber cables by allowing re-reflection of light, making it difficult to detect backscattered light efficiently.
Innovation Solution
A semiconductor light receiving device with a simple structure featuring a light absorption layer and an anti-reflection portion on a semiconductor substrate, utilizing a first metal film with a complex refractive index of 3 to 5 and a dielectric film with a refractive index of 2 or less, along with a second metal film, to prevent light re-reflection and reduce fall time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of time
If multiple light-absorption layers are used to reduce fall time, then the fall time is reduced, but the device structure becomes more complex and manufacturing cost increases
Solution Approach 1:
A reflection prevention layer is introduced as an intermediary between the light-absorption layer and the substrate. This layer prevents light reflected from the substrate from re-entering the light-absorption layer, thereby reducing fall time without requiring multiple light-absorption layers. The reflection prevention layer acts as a mediator that blocks the harmful reflected light while maintaining the simplicity of a single light-absorption layer structure.
Solution Approach 2:
The reflection prevention layer is constructed using composite materials with specific optical properties - a first layer with refractive index higher than the substrate and a second layer with refractive index lower than the first layer. This composite structure optimizes light reflection prevention while maintaining structural simplicity, resolving the contradiction between performance improvement and structural complexity.
2Reliability
If multiple light-absorption layers are used to prevent light re-entry, then light re-reflection is prevented, but manufacturing precision requirements increase due to crystal growth difficulties
Solution Approach 1:
The reflection prevention layer serves as an intermediary that eliminates the need for complex multi-layer crystal growth. By placing this layer between the light-absorption layer and substrate, it prevents reflected light from re-entering the detector, achieving reliable light re-reflection prevention through a simpler single-layer structure that is easier to manufacture with consistent precision.
Solution Approach 2:
The invention controls the refractive index parameters of the reflection prevention layer - specifically designing it with a first layer having higher refractive index than the substrate and a second layer with lower refractive index than the first. This parameter optimization ensures effective light reflection prevention while simplifying the manufacturing process and reducing precision requirements compared to multiple light-absorption layers.
3Device complexity
If a simple single light-absorption layer structure is used, then device structure is simplified, but light re-reflection occurs increasing fall time
Solution Approach 1:
A reflection prevention layer is introduced as an intermediary between the light-absorption layer and the substrate. This layer prevents light reflected from the substrate from re-entering the light-absorption layer, thereby reducing fall time without requiring multiple light-absorption layers. The reflection prevention layer acts as a mediator that blocks the harmful reflected light while maintaining the simplicity of a single light-absorption layer structure.
Solution Approach 2:
The reflection prevention layer is constructed using composite materials with specific optical properties - a first layer with refractive index higher than the substrate and a second layer with refractive index lower than the first layer. This composite structure optimizes light reflection prevention while maintaining structural simplicity, resolving the contradiction between performance improvement and structural complexity.
4Ease of manufacture
If a simple single light-absorption layer structure is used, then manufacturing cost is reduced, but light re-reflection occurs creating dead zones in defect detection
Solution Approach 1:
A reflection prevention layer is introduced as an intermediary between the light-absorption layer and the substrate. This layer prevents light reflected from the substrate from re-entering the light-absorption layer, thereby reducing fall time without requiring multiple light-absorption layers. The reflection prevention layer acts as a mediator that blocks the harmful reflected light while maintaining the simplicity of a single light-absorption layer structure.
Solution Approach 2:
The reflection prevention layer is constructed using composite materials with specific optical properties - a first layer with refractive index higher than the substrate and a second layer with refractive index lower than the first layer. This composite structure optimizes light reflection prevention while maintaining structural simplicity, resolving the contradiction between performance improvement and structural complexity.
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 effectively reduces the fall time of the semiconductor light receiving device, preventing light re-reflection and allowing for efficient detection of backscattered light, thereby minimizing the 'dead zone' and simplifying the device structure while maintaining low reflectance.
Implementation Method 1
a light receiving portion (6) having a light absorption layer (4) for absorbing the incident light
Implementation Method 2
an anti-reflection portion (11) provided in an irradiation region (10) where incident light that enters the light receiving portion (6) from the first surface side (2a) and transmitted through the light absorption layer (4) reaches, on a side of a second surface (2b) opposite to a first surface (2a) of the semiconductor substrate (2)
Implementation Method 3
a semiconductor substrate (2) transparent to incident light in an infrared region for optical communications
Data Source
AI summary
A semiconductor light receiving device (1A, 1B) having a semiconductor substrate (2) transparent to incident light in an infrared region for optical communications, a light receiving portion (6) with a light absorption layer (4) on a first surface (2a) side of the semiconductor substrate (2) to absorb the incident light, and an anti-reflection portion (11, 21) in an irradiation region (10) where incident light transmitted through the light absorption layer (4) reaches on a second surface (2b) side of the semiconductor substrate (2), the anti-reflection portion (11, 21) is formed on the second surface (2b) of the semiconductor substrate (2) by layering a first metal film (12) having a real part and imaginary part of a complex refractive index of 3 or more and 5 or less, respectively, a dielectric film (13) having a refractive index of 2 or less, and a second metal film (14).