SiGe Buffer Layer Reduces Dark Current in Waveguide-Coupled APDs
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
High-speed avalanche photodiodes (APDs) have a relatively strong dark current and are costly, making them less flexible and less suitable for high-speed optical networks like 10 Gbps PONs.
Innovation Solution
A SiGe optical buffer layer with a Ge composition of less than or equal to 20% is introduced between the Si and Ge layers, combined with an evanescent wave coupling structure, to reduce lattice mismatch and dark current while maintaining quantum efficiency and gain bandwidth product.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a high-speed APD is used to achieve high responsivity, then the power budget requirement is improved, but the dark current increases and flexibility decreases
Solution Approach 1:
A SiGe optical buffer layer is introduced as an intermediary between the Si waveguide layer and the Ge absorption layer. This buffer layer serves as a mediator that gradually transitions the crystal structure from Si to Ge, reducing lattice mismatch and dislocation density, thereby suppressing dark current while maintaining high responsivity
Solution Approach 2:
The patent uses composite material structure combining Si, SiGe, and Ge layers. The SiGe buffer layer with graded composition (increasing Ge content from bottom to top) creates a composite structure that optimizes both optical absorption and electrical performance, reducing dark current while maintaining high-speed operation
2Reliability
If a common coupling method with thick SiGe buffer layer is used, then the coupling efficiency is improved, but the component rate declines
Solution Approach 1:
The patent optimizes the thickness parameter of the SiGe buffer layer to a specific range (0.5-2.0 μm) and controls the Ge composition gradient, achieving optimal coupling efficiency without requiring excessive buffer thickness. This parameter optimization maintains high component manufacturing rates while ensuring sufficient optical coupling
3Ease of manufacture
If Si and Ge layers are directly combined, then the manufacturing process is simplified, but lattice mismatch increases causing high dark current
Solution Approach 1:
The direct Si-Ge interface is segmented into a graded SiGe buffer layer structure, where the composition transitions gradually from pure Si to pure Ge. This segmentation approach divides the abrupt interface into multiple intermediate composition layers, reducing lattice mismatch and dislocation density while remaining compatible with standard epitaxial growth processes
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
Significantly reduces dark current and maintains performance metrics, avoiding the component rate decline caused by thick SiGe buffer layers in common coupling methods.
Implementation Method 1
an evanescent wave coupling structure is used, so as to avoid a problem of a declined component rate caused by a relatively thick SiGe buffer layer that is required when a common manner of coupling front normally incident light is used
Implementation Method 2
an intrinsic-germanium (I-Ge) absorption layer (31) disposed on the GeOI substrate and configured to absorb an optical signal and generate a photo-generated carrier
Implementation Method 3
a SiGe optical buffer layer of a proper thickness is added between a Si layer and an intrinsic Ge layer, and a Ge composition in the SiGe layer is controlled to be less than or equal to 20%, which not only significantly alleviate a problem of a lattice mismatch between the Si layer and the intrinsic Ge layer
Implementation Method 4
An APD (Avalanche Photodiode, avalanche photodiode) may have very high responsivity due to a multiplication effect
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The present invention discloses an avalanche photodiode and a manufacturing method thereof, relates to the field of communications, and can resolve a problem that an existing avalanche photodiode has a relatively strong dark current. The avalanche photodiode includes: a GeOI substrate; an I-Ge absorption layer (31), configured to absorb an optical signal and generate a photo-generated carrier; a first p-type SiGe layer (23), a second p-type SiGe layer (24), a first SiGe layer (21), and a second SiGe layer (22), where a Si content in any one of the SiGe layers is less than or equal to 20%; a first SiO2 oxidation layer (72) and a second SiO2 oxidation layer (73); a first Taper type silicon Si waveguide layer (11) and a second Taper type silicon Si waveguide layer (12); a heavily-doped n-type silicon Si multiplication layer (13); and anode electrodes (61) and a cathode electrode (62).