Semiconductor Light Receiving Element With Concave Back-Surface Reflector
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Solution Overview
Problem
Semiconductor light receiving elements face challenges in achieving high response speed and sensitivity due to the need for smaller light absorption regions, which reduce light receiving area and increase sensitivity to incident position deviations, and existing solutions like convex or Fresnel lens shapes can hinder high response speed with space charge effects.
Innovation Solution
A semiconductor light receiving element with a light absorption region near the main surface and a partially spherical concave reflecting portion on the back surface, where the radius of curvature is set to balance coupling efficiency and space charge effects, allowing efficient light reflection and absorption without excessive condensation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the diameter of the light absorption region is reduced to increase response speed, then the element capacitance decreases and response frequency increases, but the light receiving area decreases and sensitivity deteriorates
Solution Approach 1:
The patent utilizes the third dimension (depth) by forming a concave reflecting portion on the back surface of the semiconductor substrate. This allows light to be reflected from below and guided to the light absorption region, effectively increasing the light receiving area without increasing the planar diameter, thus resolving the contradiction between response speed and sensitivity
Solution Approach 2:
The concave reflecting portion acts as an intermediary structure that redirects light paths. It captures light incident on the back surface and guides it to the light absorption region, enabling the system to achieve both high response speed (small absorption region diameter) and high sensitivity (effective light collection from larger area)
2Speed
If the diameter of the light absorption region is reduced to increase response speed, then the element capacitance decreases, but the sensitivity to incident position deviations increases
Solution Approach 1:
By introducing the back surface reflection dimension, the patent creates a larger effective light receiving area that is concentric with the small light absorption region. This allows the system to maintain high response speed while reducing sensitivity to incident position deviations, as light can enter through the larger concentric area and still be guided to the absorption region
Solution Approach 2:
The patent divides the light receiving function into two segments: the small light absorption region for high-speed response and the larger concentric light receiving area (formed by the incident region minus the light absorption region) for light collection. The concave reflecting portion mediates between these two segments, allowing them to function independently yet cooperatively
3Productivity
If a convex lens shape or Fresnel lens shape is used to condense light on the light absorption region, then light receiving efficiency improves, but the space charge effect increases and response speed deteriorates
Solution Approach 1:
Instead of using a convex lens shape that condenses light from the front surface, the patent inverts the approach by using a concave reflecting portion on the back surface to reflect and guide light upward to the light absorption region. This inverted configuration avoids the space charge effect while maintaining efficient light collection
Solution Approach 2:
The patent extracts the light condensing function from the front surface (removing the convex lens or Fresnel lens structure) and relocates it to the back surface through the concave reflecting portion. This extraction eliminates the harmful space charge effect while preserving the beneficial light concentrating effect
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 design achieves both high response speed and improved sensitivity by ensuring efficient light absorption and reducing sensitivity loss from incident position deviations, while maintaining a larger light receiving area than the absorption region.
Implementation Method 1
a partially spherical concave reflecting portion provided on a back surface opposite to the main surface of the semiconductor substrate and capable of reflecting incident light incident on the incident region from the main surface side of the semiconductor substrate toward the light absorbing region
Implementation Method 2
a light absorption region formed in a vicinity of a main surface of a semiconductor substrate transparent to an incident light
Data Source
AI summary
A semiconductor light receiving element comprises a light absorption region formed in the vicinity of the main surface of the semiconductor substrate transparent to the incident light; an incident region set to be concentric with and larger than the light absorption region; and a partially spherical concave reflecting portion formed on a back surface of the semiconductor substrate and capable of reflecting incident light incident on the incident region from the main surface side toward the light absorbing region; wherein, when the radius of curvature of the portion is R, the diameter of the incident region is B, the distance between the light absorbing region and the concave reflecting portion is W, and the diameter of the light absorbing region is P, then the radius of curvature R satisfies a condition of 2 BW/(B−P/2)≤R≤2BW/(B−P).