GeSi Avalanche Photodiode Strain Engineering for Extended Wavelengths
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Solution Overview
Problem
Germanium/Silicon (GeSi) avalanche photodiodes (APDs) are limited by the absorption of bulk Ge ceasing at 1550 nm, restricting their application in optical communication systems, and suffer from high dark current noise, which hampers their performance in high-speed applications.
Innovation Solution
Incorporating a top stressor layer on the Ge-containing absorption layer to increase tensile strain, allowing absorption beyond the optical bandgap and reducing dark current through graded doping profiles with p-type dopants like gallium or boron.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Illumination intensity
If bulk Ge is used for absorption layer, then optical absorption at telecommunication wavelength is excellent, but absorption ceases at 1550 nm due to bandgap limits
Solution Approach 1:
The patent applies parameter changes by introducing tensile strain to the Ge absorption layer through top stressor layers. This strain modifies the bandgap structure of Ge, enabling optical absorption beyond 1550 nm while maintaining absorption efficiency at telecommunication wavelengths. The strain parameter transformation allows the material to absorb photons with energies below the original bandgap limit.
Solution Approach 2:
The patent uses composite material structures by combining Ge absorption layer with top stressor layers (such as SiN or SiO2) and graded doping profiles. This composite approach integrates the excellent optical absorption of Ge with the bandgap engineering capability of stressor layers, creating a multi-functional structure that extends wavelength coverage while maintaining high absorption performance.
2Productivity
If GeSi APD is used for high-speed optical communication, then carrier multiplication properties are outstanding, but dark current is high causing noise
Solution Approach 1:
The patent applies local quality by implementing graded doping profiles where the doping concentration varies spatially within the absorption layer. By creating regions with different doping levels (higher at interfaces, lower in the middle), the structure locally optimizes carrier multiplication at the multiplication layer while suppressing dark current generation in the absorption region, thus resolving the contradiction between productivity and harmful factors.
3Adaptability or versatility
If top stressor layer is added to extend absorption wavelength, then absorption beyond 1550 nm is achieved, but device structure becomes more complex
Solution Approach 1:
The top stressor layers serve multiple functions simultaneously: they provide tensile strain to extend the absorption wavelength beyond 1550 nm, act as anti-reflection coatings to enhance light coupling, and can be integrated with existing CMOS fabrication processes. This multi-functionality reduces the need for additional separate components, thereby mitigating the complexity increase despite the extended wavelength capability.
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 optical absorption in wavelengths beyond 1550 nm and significantly reduces dark current, thereby improving the performance and applicability of GeSi APDs in optical communication systems.
Implementation Method 1
The at least one top stressor layer is configured to increase a tensile strain of the Ge-containing absorption layer
Implementation Method 2
An avalanche photodiode (APD) is a type of photosensitive semiconductor device in which light is converted to electricity due to the photoelectric effect
Implementation Method 3
avalanche photodiode (APD) is a type of photosensitive semiconductor device in which light is converted to electricity due to the photoelectric effect coupled with electric current multiplication as a result of avalanche breakdown
Data Source
AI summary
Avalanche photodiodes (APDs) having at least one top stressor layer disposed on a germanium (Ge)-containing absorption layer are described herein. The top stressor layer can increase the tensile strain of the Ge-containing absorption layer, thus extending the absorption of APDs to longer wavelengths beyond 1550 nm. In one embodiment, the top stressor layer has a four-layer structure, including an amorphous silicon (Si) layer disposed on the Ge-containing absorption layer; a first silicon dioxide (SiO2) layer disposed on the amorphous Si layer, a silicon nitride (SiN) layer disposed on the first SiO2 layer, and a second SiO2 layer disposed on the SiN layer. The Ge-containing absorption layer can be further doped by p-type dopants. The doping concentration of p-type dopants is controlled such that a graded doping profile is formed within the Ge-containing absorption layer to decrease the dark currents in APDs.