Gradient Germanium-Silicon Photodetector Defect Isolation
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Solution Overview
Problem
The existing methods for growing single crystal germanium on silicon substrates, such as rapid melt growth (RMG), face challenges like contamination from the silicon seed region and the formation of defects due to melting and recrystallization, leading to poor responsivity and yield in photodetectors.
Innovation Solution
A photodetector design featuring a gradient material layer with a silicon-rich region away from the incident light and a germanium-rich region near the optical signal, along with a defect gettering region outside the optical signal path, formed using a CMOS-compatible process that minimizes contamination and defect formation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If rapid melt growth technique is used to grow single crystal germanium on silicon substrate, then process compatibility is improved, but contamination from silicon seed region occurs resulting in poor photodetector responsivity
Solution Approach 1:
The photodetector structure is segmented into distinct regions: a silicon-rich region away from the incident light and a germanium-rich region near the optical signal. This segmentation allows the silicon substrate to provide mechanical support and process compatibility while the germanium-rich region maintains high photodetector responsivity by minimizing silicon contamination in the active detection area.
Solution Approach 2:
The patent applies local quality by creating a gradient material composition where the germanium mole fraction varies spatially. The region near the optical signal has high germanium concentration for optimal photodetection, while the region away from the signal has higher silicon content for substrate compatibility. This local variation in material composition resolves the contradiction between process compatibility and responsivity.
2Stability of the object's composition
If melting and recrystallization process is applied in RMG technique, then single crystal germanium can be formed, but defects are formed near the end of photodetector affecting yield and responsivity
Solution Approach 1:
The patent extracts or removes the defective region from the active photodetector structure. By designing a gradient composition where defects concentrate in the silicon-rich region away from the optical signal, the harmful defects are effectively separated from the germanium-rich active detection region, preserving both single crystal structure and photodetector performance.
Solution Approach 2:
The patent converts the harmful effect of defect formation during melting and recrystallization into a beneficial outcome. The gradient material composition causes defects to preferentially form in the silicon-rich region, which is intentionally positioned away from the optical signal path. Thus, the defect formation process is redirected to a non-critical region, maintaining high responsivity in the germanium-rich active region.
3Reliability
If gradient material layer with silicon-rich region is used away from incident light, then contamination is minimized, but manufacturing complexity increases
Solution Approach 1:
The patent employs parameter changes by varying the germanium mole fraction as a continuous gradient through the material layer. This gradient composition is achieved through controlled deposition or growth processes where the germanium concentration transitions from high near the optical signal to low away from it. This parameter variation enables contamination control while using standard CMOS-compatible manufacturing techniques.
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 design enhances the responsivity and yield of photodetectors by isolating defects from the active photodetector region and maintaining a high germanium mole fraction, thereby improving the conversion of optical signals to electrical signals.
Implementation Method 1
The photodetector material, an active region, absorbs energy from the photons of the transmitted optical signal, which, in response, excites charge carriers, e.g., electrons and holes
Implementation Method 2
A photodetector design featuring a gradient material layer with a silicon-rich region away from the incident light and a germanium-rich region near the optical signal, along with a defect gettering region outside the optical signal path
Implementation Method 3
The lattice constant of germanium is not perfectly matched with the lattice constant of silicon; the lattice constant of germanium is slightly larger than that of silicon. The mismatch between the lattice constants of germanium and silicon presents problems for using a regular epitaxial growth technique
Data Source
AI summary
Photodetector including: a waveguide of a waveguide material extending over a substrate; an insulating layer formed over the waveguide and having an opening exposing the waveguide; a photodetector layer formed over the insulating layer and into the opening so as to make contact with the waveguide, the photodetector layer having a first end at the opening and a second end distal from the opening, the photodetector layer being a gradient material of the waveguide material and germanium wherein a waveguide material portion of the gradient material varies from a maximum at the first end to a minimum at the second end and wherein a germanium portion of the gradient material varies from a minimum at the first end to a maximum at the second end; a photodetector region at the second end; and a photodetector layer extension extending at an angle from the photodetector layer at the second end.