Side-Contact Photodiode Structure for Fast, Sensitive Light Reception
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Solution Overview
Problem
Semiconductor light-receiving elements face a trade-off between light reception sensitivity and operating speed, where increasing the light-absorbing layer thickness enhances sensitivity but decreases speed, and reducing the ring-shaped electrode width to increase speed complicates manufacturing and increases contact resistance, making it difficult to achieve high-speed operation with high sensitivity.
Innovation Solution
A semiconductor light-receiving element with a metal electrode contacting the side of a semiconductor layer doped with impurities, where the electrode is formed on a surface parallel to the growth direction, allowing for a larger light-receiving diameter and increased process margin without sacrificing sensitivity, by reducing contact resistance and improving adhesion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the light-absorbing layer thickness is increased to improve light reception sensitivity, then the sensitivity increases, but the operating speed decreases due to longer carrier transit time
Solution Approach 1:
The patent transitions from a conventional planar electrode configuration to a vertical side-contact configuration. The metal electrode contacts the semiconductor layer from the side surface rather than from the top surface, creating a three-dimensional contact geometry. This dimensional change allows the electrode to be positioned closer to the light-absorbing region without occupying the optical path, thereby improving sensitivity while maintaining fast response through reduced carrier collection distance.
2Speed
If the ring-shaped electrode width is reduced to improve operating speed, then the capacitance decreases and speed increases, but the manufacturing precision and adhesion deteriorate
Solution Approach 1:
The patent moves the electrode contact from a two-dimensional top-surface ring configuration to a three-dimensional side-surface configuration. This allows the electrode to wrap around or contact the semiconductor from the side, providing extended contact area and improved adhesion without requiring precise control of narrow top-surface features. The vertical contact geometry naturally provides mechanical support and larger bonding area.
Solution Approach 2:
The metal electrode structure is designed to surround or envelop portions of the semiconductor layer from the side, creating a nested configuration where the electrode partially encloses the semiconductor structure. This nested geometry provides multiple contact points and distributed adhesion areas, improving both manufacturing robustness and electrical contact reliability while maintaining the low-capacitance benefit of reduced top-surface footprint.
3Reliability
If a reflective mirror is added to increase the optical path length, then the light reception sensitivity improves, but the device complexity increases
Solution Approach 1:
The patent achieves extended optical path length without adding top-surface reflective mirrors by utilizing the vertical dimension. The side-contact electrode configuration allows the light to traverse the semiconductor layer vertically multiple times or along extended three-dimensional paths before being collected, effectively increasing the interaction length between light and absorber material without requiring additional optical components on the top surface.
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 enables high-speed operation with maintained light reception sensitivity and increased manufacturing process margin by reducing contact resistance and improving adhesion, allowing for a larger light-receiving diameter and efficient electrical signal extraction.
Implementation Method 1
semiconductor light-absorbing layer having bandgap energy adjusted to absorb incident light
Implementation Method 2
signal light is incident from the back side of the InP substrate 101 of the semiconductor light-receiving element 100, and is reflected off the reflective mirror 105 on the top portion of the element
Data Source
AI summary
Provided is a semiconductor light receiving element which can achieve a high-speed operation without sacrificing light receiving sensitivity while increasing the margin of a manufacturing process. The semiconductor light receiving element according to the present invention is characterized by comprising: a semiconductor layer doped with a first impurity; a semiconductor light absorption layer in which a band gap energy is adjusted to absorb incident light on the semiconductor layer doped with the first impurity; a semiconductor layer on the semiconductor light absorption layer and doped with a second impurity; and a metal electrode contacting side surfaces of the semiconductor layer doped with the second impurity, wherein side surfaces of the metal electrode are surfaces parallel to a growth direction of the semiconductor layer doped with the second impurity.