Evanescently Coupled Germanium Photodiode for High-Bandwidth Detection
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Solution Overview
Problem
Silicon-based optical devices face limitations in generating and absorbing light at wavelengths used for optical communication due to silicon's poor performance, while III-V semiconductors are expensive and less compatible with silicon fabrication processes.
Innovation Solution
A semiconductor-based photodiode is coupled with an optical waveguide, using germanium as the photodetector material, which is efficiently coupled evanescently to control light absorption in a high electric field region, minimizing absorption in low field regions and enhancing bandwidth.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If silicon-based waveguides are used for optical devices, then waveguide fabrication is excellent with submicron dimensions, but light generation and absorption at optical communication wavelengths is poor
Solution Approach 1:
The patent employs a composite structure combining silicon waveguides with germanium photodiodes. The silicon provides excellent waveguide fabrication with submicron dimensions, while the germanium layer integrated on the silicon substrate provides efficient light absorption at optical communication wavelengths (1310 nm and 1550 nm). This composite approach resolves the contradiction by allowing each material to perform its strength: silicon for precise waveguiding and germanium for reliable photodetection.
2Reliability
If III-V semiconductors are used for photodetectors, then light absorption performance is improved, but fabrication cost increases and compatibility with Si fabrication processes decreases
Solution Approach 1:
The patent merges germanium photodiode fabrication with existing silicon CMOS fabrication processes. The germanium layer is deposited and processed on the silicon substrate using techniques that are compatible with standard silicon manufacturing, allowing the photodetector to achieve III-V level performance while maintaining silicon process compatibility and cost-effectiveness. This integration eliminates the need for separate III-V semiconductor fabrication lines.
3Ease of operation
If photodiode is directly coupled with waveguide, then coupling is simple, but light absorption occurs in low-field regions reducing bandwidth
Solution Approach 1:
The patent introduces an evanescent field coupling mechanism as an intermediary between the waveguide and photodiode. Instead of direct physical contact, the waveguide is positioned close to the photodiode such that the evanescent field of the guided mode extends into the germanium absorption region. This intermediary coupling method maintains simplicity while ensuring that light absorption occurs primarily in high-field regions of the photodiode, preserving bandwidth performance.
4Productivity
If optical waveguide is spaced apart from semiconductor layer, then evanescent coupling is achieved for bandwidth enhancement, but coupling efficiency decreases
Solution Approach 1:
The patent optimizes the spacing parameter between the waveguide and photodiode to achieve the desired balance. By carefully controlling the gap distance, the evanescent field coupling is maximized to provide sufficient bandwidth enhancement while maintaining adequate coupling efficiency. The spacing is tuned so that the evanescent field extends sufficiently into the germanium layer for effective absorption without being so large as to cause excessive loss.
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 supports higher bandwidths (up to 60 GHz) at higher optical signal intensities by optimizing light absorption in the photodiode, improving the performance of optical detectors.
Implementation Method 1
an optical waveguide spaced apart from the semiconductor layer and evanescently coupled with a depletion region of the photodiode
Data Source
AI summary
Embodiments described herein include an apparatus comprising a semiconductor-based photodiode disposed on a semiconductor layer, and an optical waveguide spaced apart from the semiconductor layer and evanescently coupled with a depletion region of the photodiode. The photodiode may be arranged as a vertical photodiode or a lateral photodiode.