Waveguide Photodiode Buffer Layer Reduces Parasitic Capacitance
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-frequency response of waveguide photodiodes is hindered by increased parasitic capacitance due to a thinned absorption layer, which is necessary to shorten minority carrier transit time in optical receivers for high-speed optical communication systems.
Innovation Solution
A functional optical device with a waveguide photodiode integrated on a semiconductor substrate, featuring an absorption layer sandwiched between p-type and n-type cladding layers, including an un-doped or lightly doped n-type buffer layer to reduce parasitic capacitance while maintaining short minority carrier transit times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If the absorption layer is thinned to shorten minority carrier transit time, then high frequency response is improved, but parasitic capacitance increases which deteriorates high frequency response
Solution Approach 1:
The n-type layer is segmented into two distinct regions: a first n-type layer with higher impurity density and a second n-type layer with lower impurity density. This segmentation allows the first layer to provide low resistance contact while the second layer minimizes parasitic capacitance, thereby resolving the contradiction between reducing transit time and minimizing parasitic capacitance for improved high frequency response.
Solution Approach 2:
Different regions of the n-type layer are assigned different impurity densities to fulfill different functional requirements. The first n-type layer (closer to the absorption layer) has higher impurity density to ensure efficient carrier collection, while the second n-type layer (closer to the substrate) has lower impurity density to reduce parasitic capacitance. This local differentiation resolves the contradiction by optimizing each region for its specific function.
2Speed
If the absorption layer is thinned to reduce transit time, then response speed is improved, but device complexity increases due to additional layer structure
Solution Approach 1:
The second n-type layer serves multiple functions simultaneously: it acts as a buffer between the absorption layer and the substrate, provides electrical connection, and most importantly, reduces parasitic capacitance due to its lower impurity density. By making this layer multi-functional, the patent achieves improved response speed without proportionally increasing device complexity, as the same structural element addresses multiple requirements.
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
Enhances high-frequency response by reducing parasitic capacitance without elongating minority carrier transit times, thereby improving signal processing efficiency in optical communication systems.
Implementation Method 1
the waveguide PD receives photons from the optical waveguide along an absorption layer
Implementation Method 2
The core layer in the optical waveguide is sandwiched by the cladding layer and the n-type layers including the n-type conducting layer and the buffer layer, which also forms an optical confinement structure
Data Source
AI summary
A functional optical device is disclosed. The functional optical device integrates a coupling unit, a waveguide photodiode (PD) and an optical waveguide on a semiconductor substrate. The coupling unit extracts an optical signal by performing interference of signal light with local light. The optical waveguide carries the optical signal from the coupling unit to the waveguide PD. The semiconductor substrate provides a heavily doped conducting layer and a buffer layer that is un-doped or lightly doped with n-type impurities by density smaller than density of impurities in the heavily doped conducting layer. The conducting layer and the buffer layer continuously and evenly extend from the optical waveguide to the waveguide PD.