Inversion-Layer APD Structure for Faster Vertical Carrier Transport
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Solution Overview
Problem
Avalanche photodiodes (APDs) with lateral carrier paths face speed limitations due to carrier transit time in the Germanium absorption region and multiplication region in silicon, limiting their response.
Innovation Solution
The APD design incorporates a buried oxide layer with a lightly doped silicon region forming an inversion layer at the interface with the oxide, which acts as a cathode for a vertical electrical field, allowing photo carriers to travel vertically, reducing the thickness of the multiplication region and enhancing response.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If lateral carrier paths are used in APD with Germanium absorption region and silicon multiplication region, then device structure is simplified and easier to manufacture, but carrier transit time increases causing speed limitation
Solution Approach 1:
The patent transitions from lateral carrier transport to vertical carrier transport by changing the spatial dimension of charge carrier movement. The electric field is oriented vertically through the inversion layer at the silicon-oxide interface, causing carriers to move vertically through the absorption region and multiplication region, thereby reducing the effective path length and transit time while maintaining structural simplicity.
2Speed
If multiplication region thickness is reduced to improve response time, then speed performance improves, but device complexity increases due to need for inversion layer and vertical field configuration
Solution Approach 1:
The inversion layer at the silicon-oxide interface serves as an intermediary structure that enables vertical electric field formation without requiring complex doping profiles or additional components. This intermediate inversion layer mediates between the oxide layer and the silicon multiplication region, creating the necessary vertical field with minimal structural complexity.
Solution Approach 2:
The patent utilizes parameter changes in the oxide layer (specifically positive charge density) to create the inversion layer effect. By changing the electrical parameters at the interface between oxide and silicon, the system achieves vertical field formation with minimal structural modification, thereby improving response time without proportionally increasing device 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
This configuration results in reduced carrier transit times and improved APD performance by creating a thinner vertical electric field, enabling faster response and higher efficiency compared to lateral electric fields.
Implementation Method 1
the APD includes a vertical electrical field in the germanium absorption region, the P doped region, the lightly doped region, and the inversion layer
Implementation Method 2
a germanium absorption region above the P doped region
Implementation Method 3
a multiplication region formed from doped silicon placed on a silicon on insulator (SOI) layer
Data Source
AI summary
Embodiments herein describe an APD with a vertical electric field. In one embodiment, to reduce the thickness of the vertical electric field, an inversion layer at the interface between N doped silicon and an oxide is used as a cathode for the vertical electric field.