Ge Electro-absorption Modulator Vertical PIN Junction
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Solution Overview
Problem
Conventional Ge-based electro-absorption modulators (EAMs) face limitations in electric field strength and suffer from high optical losses due to the use of doped polycrystalline silicon or metal, which also increase fabrication complexity.
Innovation Solution
A Ge-based EAM structure featuring a vertical PIN junction (VPIN) is developed, utilizing a Ge or GeSi layer with intrinsic and doped regions to generate a vertical electric field without the need for highly-doped polycrystalline silicon or metal, allowing for higher electric field strengths and reduced optical losses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If doped polycrystalline silicon or metal is used on top of Ge or GeSi to generate electric field, then electric field strength is improved, but optical losses increase due to high absorption of these materials
Solution Approach 1:
The patent extracts and removes the problematic doped polycrystalline silicon or metal materials from the device structure. Instead of using these high-absorption materials to generate the electric field, the invention employs an intrinsic Ge or GeSi layer that does not absorb near-infrared light, thereby eliminating the source of optical losses while maintaining the necessary electric field generation capability through the PIN junction structure
Solution Approach 2:
The patent introduces an intrinsic Ge or GeSi layer as an intermediary material between the doped regions. This intrinsic layer serves as the active region where the electric field is generated through the PIN junction without causing significant optical absorption, thus mediating between the need for strong electric fields and the requirement for low optical losses
2Force
If conventional EAM structure with doped polycrystalline silicon or metal is used, then electric field generation is achieved, but fabrication complexity increases
Solution Approach 1:
The patent extracts and eliminates the complex multi-material stack of doped polycrystalline silicon or metal layers required in conventional EAMs. The invention simplifies the fabrication by using only intrinsic Ge or GeSi layers combined with standard Si waveguide layers, removing the need for complex material deposition and processing steps associated with polycrystalline silicon and metal integration
Solution Approach 2:
The patent changes the material parameters from complex multi-material compositions (doped polycrystalline silicon, metal) to simpler intrinsic Ge or GeSi materials. This parameter change in material composition and structure reduces the number of fabrication steps, eliminates the need for specialized processing of polycrystalline silicon and metal, and simplifies the overall device fabrication process
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
The VPIN junction design enables the generation of larger electric fields and reduces optical losses, improving the modulation efficiency and performance of the EAM without adding fabrication complexity.
Implementation Method 1
by exploiting the Franz-Keldysh effect in a bulk semiconductors, which is a change in the absorption spectrum of a bulk semiconductor in the presence of an applied electric field
Implementation Method 2
by exploiting the quantum-confined Stark effect in semiconductor quantum-well structures. The quantum-confined Stark effect describes the shift of discrete electron states to lower energy levels (and correspondingly discrete hole states to higher energy levels), when an external electric field is applied across a quantum-well
Data Source
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AI summary
The present invention relates to an electro-absorption modulator (EAM) 100) and to a fabrication method thereof. The EAM 100 comprises a first conductivity type Si layer 101 and a second conductivity type Si layer 102. Further, it comprises a Ge layer 103 provided partly on the first conductivity type Si layer 101 and partly on the second conductivity type Si layer 102. The Ge layer 103 specifically includes an intrinsic lower region 104 and a second conductivity type upper region 105.