Optical Modulator Structure to Reduce P-Type Dopant Diffusion
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Solution Overview
Problem
The diffusion of p-type dopants between semiconductor layers in optical modulators leads to increased p-type dopant concentration in the core layer, causing electric field leakage and optical loss due to free carrier absorption.
Innovation Solution
The optical modulator design includes a first and second mesa waveguide with an inclined joining surface between semiconductor layers, reducing the likelihood of p-type dopant diffusion and electric field leakage, and a manufacturing method that forms a recess in the second semiconductor layer to minimize interdiffusion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If p-type semiconductor layers are used in mesa waveguides, then electrical conductivity is improved, but p-type dopant diffusion into the core layer causes electric field leakage and optical loss
Solution Approach 1:
An n-type third semiconductor layer is introduced as an intermediary between the p-type second semiconductor layer and the core layer. This n-type layer acts as a barrier that prevents p-type dopant diffusion into the core layer while maintaining electrical conductivity through the structure. The n-type layer serves as a mediator that resolves the conflict between needing p-type conductivity and preventing dopant contamination.
Solution Approach 2:
The semiconductor structure is segmented into distinct regions with different conductivity types. Instead of using a continuous p-type structure, the waveguide is divided into p-type first semiconductor layer, core layer, p-type second semiconductor layer, and n-type third semiconductor layer. This segmentation isolates the p-type dopant sources from the core layer, preventing diffusion while maintaining overall electrical functionality.
2Object-generated harmful factors
If a recess is formed in the second semiconductor layer, then dopant diffusion is reduced, but manufacturing complexity increases
Solution Approach 1:
The recess is formed in the second semiconductor layer before depositing the n-type third semiconductor layer. This preliminary action creates a physical barrier structure that prevents dopant diffusion from occurring during subsequent processing steps. By preparing the recess in advance, the design proactively prevents the diffusion problem rather than attempting to correct it later.
Solution Approach 2:
The structure combines different semiconductor materials with different properties in a composite architecture. The p-type second semiconductor layer and n-type third semiconductor layer are combined, with the recess providing a physical and chemical barrier. This composite structure leverages the different properties of p-type and n-type semiconductors to achieve both conductivity and dopant prevention.
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 suppresses p-type dopant concentration in the core layer, reducing electric field leakage and optical loss, thereby enhancing the performance of the optical modulator.
Implementation Method 1
The diffusion of p-type dopants between semiconductor layers in optical modulators leads to increased p-type dopant concentration in the core layer, causing electric field leakage and optical loss due to free carrier absorption
Implementation Method 2
forming a recess in the second semiconductor layer by wet-etching the second semiconductor layer
Data Source
AI summary
An optical modulator includes a first mesa waveguide extending in a first direction, and a second mesa waveguide. The first mesa waveguide includes a p-type first semiconductor layer disposed over a substrate, a core layer disposed over the first semiconductor layer, a p-type second semiconductor layer disposed over the core layer, and an n-type third semiconductor layer disposed over the core layer. The second semiconductor layer and the third semiconductor layer are arranged adjacent to each other in the first direction. An electrode is disposed over the third semiconductor layer. A joining surface between the second semiconductor layer and the third semiconductor layer is inclined with respect to a surface orthogonal to the first direction.