Semiconductor Light Detecting Element With Irregular Asperity
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Solution Overview
Problem
Semiconductor light detecting elements using silicon substrates face challenges in achieving satisfactory spectral sensitivity in the near-infrared wavelength band due to increased size and dark current issues with thick substrates, which also impede response speed.
Innovation Solution
The formation of irregular asperities on the surface of the semiconductor layer within the light detecting element causes light to be reflected, scattered, or diffused, increasing its travel distance within the substrate, enhancing sensitivity in the near-infrared band while reducing dark current through carrier recombination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the thickness of the silicon substrate is increased to enhance spectral sensitivity on the long wavelength side, then the sensitivity in the near-infrared wavelength band improves, but the size of the semiconductor light detecting element increases, dark current increases, and response speed decreases
Solution Approach 1:
The invention divides the silicon substrate into two distinct functional layers: a first semiconductor layer with higher impurity concentration for carrier recombination and dark current suppression, and a second epitaxial semiconductor layer with lower impurity concentration for light detection. This segmentation allows each layer to perform its specific function optimally, resolving the contradiction between sensitivity and dark current.
Solution Approach 2:
The invention applies different impurity concentrations to different regions of the silicon substrate. The first semiconductor layer has a higher impurity concentration (1×10^16 to 1×10^18 atoms/cm³) to induce carrier recombination and reduce dark current, while the second epitaxial layer has a lower impurity concentration (1×10^12 to 1×10^14 atoms/cm³) to enhance light absorption and detection sensitivity in the near-infrared band.
2Measurement precision
If the thickness of the silicon substrate is increased to enhance spectral sensitivity on the long wavelength side, then the sensitivity in the near-infrared wavelength band improves, but the response speed decreases
Solution Approach 1:
The segmented structure separates the functions of light absorption (second epitaxial layer) and carrier recombination (first semiconductor layer). This allows the detection layer to be optimized for sensitivity while the substrate layer handles carrier management, improving response speed without sacrificing near-infrared sensitivity.
Solution Approach 2:
By concentrating the impurity concentration in the first semiconductor layer rather than uniformly distributing it throughout a thick substrate, the invention creates localized carrier recombination zones. This reduces the overall carrier transit distance and improves response speed while maintaining the thickness needed for near-infrared absorption in the second layer.
3Measurement precision
If the thickness of the silicon substrate is increased to enhance spectral sensitivity on the long wavelength side, then the sensitivity in the near-infrared wavelength band improves, but the size of the semiconductor light detecting element increases
Solution Approach 1:
The invention segments the silicon substrate into two functional layers with different thicknesses optimized for their specific purposes. The first semiconductor layer can be thinner since its primary function is carrier recombination, while the second epitaxial layer provides the necessary thickness for near-infrared absorption. This segmented approach achieves the required sensitivity with a smaller overall device size compared to a uniformly thick substrate.
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 improves sensitivity characteristics in the near-infrared wavelength band and reduces dark current, allowing for more efficient light detection without the need for guard rings, thus enhancing the semiconductor light detecting element's performance.
Implementation Method 1
Light incident into the semiconductor light detecting element is reflected, scattered, or diffused on the surface with the irregular asperity therein to travel through a long distance in the silicon substrate
Implementation Method 2
Light incident into the semiconductor light detecting element is reflected, scattered, or diffused on the surface with the irregular asperity therein to travel through a long distance in the silicon substrate
Implementation Method 3
This allows the light incident into the semiconductor light detecting element to be absorbed mostly in the silicon substrate to generate charge
Implementation Method 4
the silicon substrate has the semiconductor layer with the higher impurity concentration than the epitaxial semiconductor layer, it induces recombination of unnecessary carriers generated independently of light on the surface side of the semiconductor layer. This recombination results in reduction in dark current
Implementation Method 5
The semiconductor layer prevents carriers generated by light near the surface of the semiconductor layer from being trapped in the surface. For this reason, charge generated by light efficiently migrates to the photosensitive region
Data Source
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AI summary
A semiconductor light detecting element 1A is provided with a silicon substrate 2 having a semiconductor layer 20, and an epitaxial semiconductor layer 21 grown on the semiconductor layer 20 and having a lower impurity concentration than the semiconductor layer 20; and conductors provided on a surface of the epitaxial semiconductor layer 21. A photosensitive region is formed in the epitaxial semiconductor layer 21. Irregular asperity 22 is formed at least in a surface 2BK opposed to the photosensitive region in the semiconductor layer 20. The irregular asperity 22 is optically exposed.