Stacked Photodiode Structure for High-Speed Self-Bias Operation
Solution Overview
Problem
Conventional semiconductor photosensitive elements require an external bias voltage for high-speed operation, which complicates their design and reduces light receiving sensitivity due to the need for additional components like ohmic layers that hinder light transmission and increase resistance.
Innovation Solution
A semiconductor photosensitive element is designed with a stacked structure of multiple photodiodes, where one diode generates a bias voltage internally, eliminating the need for external bias and enhancing high-frequency operation by separating high-frequency and DC current paths through distinct junctions and electrode configurations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a reverse bias is applied from the outside to enable high-speed operation, then the operation speed is improved, but the device complexity increases due to the need for feed lines and external bias voltage sources
Solution Approach 1:
The patent implements self-service by stacking multiple photodiodes where one or more photodiodes generate bias voltage internally to supply other photodiodes in the stack. This eliminates the need for external feed lines and bias voltage sources, reducing device complexity while maintaining high-speed operation capability. The generated bias voltage is used to create depletion layers and electric fields within the photodiode stack itself.
2Ease of operation
If an ohmic layer is inserted between pin junctions to enable DC current flow, then the ease of operation is improved, but the light receiving sensitivity deteriorates due to the layer blocking light and having high resistance
Solution Approach 1:
The patent extracts and eliminates the problematic ohmic layer from the structure. Instead of inserting an ohmic layer between pin junctions that blocks light and has high resistance, the invention uses a stack configuration where photodiodes are connected through their inherent p-n junctions. The stacking arrangement allows DC current to flow through the series connection of junctions without requiring additional ohmic layers, thus maintaining light receiving sensitivity while enabling proper current flow.
3Ease of operation
If two PDs are stacked to generate internal bias, then the ease of operation is improved by eliminating external bias, but the operation speed deteriorates because currents in reverse directions cancel each other out
Solution Approach 1:
The patent applies local quality by creating different functional regions within the photodiode stack. One or more photodiodes in the stack are designated as bias-generating elements that produce voltage in a specific direction, while other photodiodes are optimized for high-speed signal detection. The current directions are arranged so that the bias-generating photodiodes produce current in one direction while the signal-detecting photodiodes operate with currents in opposite directions, preventing cancellation and maintaining high-speed operation capability.
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 configuration allows for high-speed operation without external bias, maintaining high light receiving sensitivity by using metal electrodes outside the light receiving region and optimizing the thickness of absorption layers for balanced current generation across diodes.
Implementation Method 1
a first light absorption layer, a first semiconductor layer of a second conductivity type, a first semiconductor layer of the first conductivity type, a second light absorption layer
Data Source
AI summary
A semiconductor photosensitive element comprises: a semiconductor substrate of a first conductivity type; a first light absorption layer, a first semiconductor layer of a second conductivity type, a first semiconductor layer of the first conductivity type, a second light absorption layer, and a second semiconductor layer of a second conductivity type, arranged in this order on the semiconductor substrate; a first electrode connected the second semiconductor layer of the second conductivity type; a second electrode connected to the semiconductor substrate; and a third electrode electrically connecting the first semiconductor layer of the first conductivity type to the first semiconductor layer of the second conductivity type. The third electrode is located outside a light detection region for detecting optical signals.