Photodetector Anode-Cathode Side-Edge Contacts
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Solution Overview
Problem
Current photodetectors, particularly those using germanium, face challenges in reducing operating voltage, enhancing gain, and improving bandwidth and responsivity while maintaining low capacitance and integrating well with low-voltage CMOS technologies.
Innovation Solution
The structure for a photodetector includes a light-absorbing region with anode-cathode pairs positioned along its side edges, formed using a semiconductor-on-insulator substrate with shallow trench isolation regions and selective deposition of germanium, allowing for reduced operating voltage and enhanced avalanche gain without contacts on the light-absorbing region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If conventional photodetector structures are used, then the device can detect light, but the operating voltage is high and gain is low
Solution Approach 1:
The patent transitions from conventional top-contact photodetector geometry to side-edge contact geometry. The anode and cathode are positioned at the side edges of the light-absorbing region rather than on top, creating a lateral electric field configuration that enables avalanche multiplication and reduces operating voltage while maintaining detectability.
Solution Approach 2:
The patent creates localized high electric field regions at the side edges of the light-absorbing germanium region where the anode and cathode contacts are positioned. This local field enhancement enables avalanche gain specifically at the contact interfaces while the bulk of the light-absorbing region maintains optimal conditions for photon absorption and carrier generation.
2Reliability
If germanium is used for high infrared absorption, then responsivity improves, but capacitance increases
Solution Approach 1:
By moving the contacts to the side edges and creating a lateral field configuration, the patent reduces the overlap area between the electric field and the light-absorbing germanium region. This geometric reconfiguration maintains the high infrared absorption and responsivity of germanium while minimizing the capacitive coupling between the contacts and the absorber.
3Ease of operation
If contacts are placed on the light-absorbing region, then electrical connection is achieved, but operating voltage increases and gain decreases
Solution Approach 1:
The patent moves the electrical contacts from the vertical top surface to the lateral side edges of the light-absorbing region. This dimensional change in contact placement enables the formation of a lateral p-n junction that produces high electric fields for avalanche multiplication, achieving both good electrical connection and low operating voltage with high gain.
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 reduces operating voltage, increases gain, enhances bandwidth, and improves responsivity by creating high electric fields and minimizing carrier transit time, while being readily integrable with low-voltage CMOS technologies.
Implementation Method 1
The germanium photodetector converts modulated pulses of light into current as photons of electromagnetic radiation are absorbed in the germanium
Implementation Method 2
enhanced avalanche gain without contacts on the light-absorbing region
Data Source
AI summary
Structures for a photodetector and methods of fabricating a structure for a photodetector. The structure includes a light-absorbing region having a side edge, an anode adjacent to the side edge of the light-absorbing region, and a cathode adjacent to the side edge of the light-absorbing region.