GeSi Avalanche Photodiode Strain Engineering and Graded Doping
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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
The introduction of a top stressor layer on the Ge absorption layer increases tensile strain, enhancing absorption beyond 1550 nm, and a graded doping profile with p-type dopants reduces dark currents, thereby improving the spectral response and sensitivity of APDs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
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 limitation
Solution Approach 1:
The patent applies strain engineering by introducing top stressor layers (such as SiN or SiO2) and bottom stressor layers to induce tensile strain in the Ge absorption layer. This strain modifies the bandgap structure of Ge, enabling optical absorption beyond the natural 1550 nm bandgap limitation and extending the spectral response to 1650 nm and beyond.
Solution Approach 2:
The patent creates a composite structure combining Ge absorption layer with stressor layers (SiN, SiO2, SiGe) and doping layers (p-type and n-type). This composite approach allows the Ge layer to maintain its excellent absorption properties while the stressor layers modify its optical characteristics to extend absorption beyond the natural bandgap limit.
2Device complexity
If conventional doping is used in GeSi APD, then device structure is simple, but dark current is high which limits high-speed performance
Solution Approach 1:
The patent implements a graded doping profile where doping concentration varies spatially within the absorption layer. P-type dopants are introduced with concentrations ranging from 1×10^18 to 1×10^20 atoms/cm³, creating localized regions of different doping levels. This local variation in doping quality reduces dark current while maintaining the overall device structure.
Solution Approach 2:
The patent changes the doping parameter by introducing graded doping profiles with specific concentration ranges (p-type: 1×10^18 to 1×10^20 atoms/cm³, n-type: 1×10^17 to 1×10^19 atoms/cm³). This parameter modification effectively reduces dark current generation while preserving the structural simplicity needed for manufacturing.
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 solution extends the absorption range of GeSi APDs to 1650 nm and significantly reduces dark current, enhancing their performance and sensitivity for high-speed optical communication applications.
Implementation Method 1
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 2
The at least one top stressor layer may be configured to increase a tensile strain in the Ge absorption layer such that absorption of the Ge absorption layer between 1550 nm and 1650 nm is increased
Implementation Method 3
The absorption layer can be further doped with p-type dopants. The doping concentration of the p-type dopants is controlled such that a graded doping profile is formed within the absorption layer to decrease the dark currents of APDs
Implementation Method 4
APDs differ from conventional photodiodes in that incoming photons internally trigger a charge avalanche in APDs, thus APDs can measure light of even lower level
Data Source
AI summary
Avalanche photodiodes (APDs) having at least one top stressor layer disposed on a germanium (Ge) absorption layer are described herein. The top stressor layer can increase the tensile strain of the Ge 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 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 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 absorption layer to decrease the dark currents in APDs.