Germanium Photodetector Dark Current Reduction via Segmentation
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Solution Overview
Problem
Conventional germanium photodetectors experience high dark current levels, which degrade the signal-to-noise ratio and increase power consumption, limiting transmission distance in optical communication systems.
Innovation Solution
The solution involves reducing the area of the germanium layer's surface contact with the electrode and utilizing multiple germanium layers in series to minimize threading dislocations, thereby reducing dark current without compromising photocurrent levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a germanium layer is formed on a silicon substrate to enable light absorption and photocurrent generation, then the photodetector can detect optical signals, but threading dislocations occur at the germanium-silicon interface that increase dark current
Solution Approach 1:
The germanium layer is divided into multiple thin sub-layers (e.g., four layers of 5nm each) instead of a single thick layer. This segmentation reduces the total threading dislocation density because each thin layer has fewer dislocations, and the cumulative effect maintains sufficient light absorption while lowering dark current generation at interfaces.
Solution Approach 2:
The patent applies different doping concentrations to different regions of the germanium layer. The first germanium layer has a lower doping concentration (1×10^18 to 1×10^19 atoms/cm³) while subsequent layers have higher doping concentrations (1×10^19 to 1×10^20 atoms/cm³). This local quality variation optimizes both light absorption in lower-doped regions and carrier collection in higher-doped regions, while managing dark current.
2Reliability
If the germanium layer area is increased to improve light absorption and photocurrent, then detection sensitivity improves, but the dark current increases due to larger surface contact area with electrodes
Solution Approach 1:
By segmenting the germanium layer into multiple thin layers, the patent achieves sufficient light absorption path length without requiring a large lateral area. The stacked configuration allows light to pass through multiple interfaces, increasing absorption probability while keeping the electrode contact area small, thus maintaining photocurrent while reducing dark current.
Solution Approach 2:
The patent transitions from a single-plane germanium layer to a multi-layer stacked configuration in the vertical dimension. This dimensional change increases the effective light absorption volume without proportionally increasing the lateral surface area contact with electrodes, thereby improving photocurrent generation while limiting dark current pathways.
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 approach effectively decreases dark current, enhancing the signal-to-noise ratio and increasing transmission distance while maintaining sufficient photocurrent levels, leading to improved power efficiency and performance in optical communication devices.
Implementation Method 1
Once light enters the core layer 110 and the light is absorbed by the germanium layer 114, then a photocurrent flows between the electrode 117 and the electrodes 116, 118
Data Source
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AI summary
The present invention provides a germanium photodetector which reduces a dark current without degradation of a photocurrent. The germanium photodetector includes: a silicon substrate; a lower clad layer formed on the silicon substrate; a core layer (210) formed on the lower clad layer; a p-type silicon slab (211) formed in a part of the core layer (210) and doped with a p-type impurity ion; p++ silicon electrode sections (212, 213) that are highly-doped with a p-type impurity and act as an electrode; and germanium layers (241, 242) which absorb light. The germanium photodetector further includes an upper clad layer, an n-type germanium region doped with an n-type impurity above the germanium layer, and an electrode. According to the present invention, two germanium layers (241, 242) are provided on the p-type silicon slab (211) so as to miniaturize the area of the surface of the individual germanium layer in contact with the p-type silicon slab (211), so that the dark current due to threading dislocation can be reduced.