Silicon-Cap APD Structure for Hot Carrier Injection Control
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Avalanche photodiodes (APDs) suffer from hot carrier injection (HCl) degradation due to photo carriers being scattered and injected into the surrounding oxide, leading to a distortion of the electric field and reduced photocurrent gain over time.
Innovation Solution
The APD architecture includes a silicon cap layer forming a larger multiplication region on top of a germanium absorption region, with a charge layer formed using in-situ doping to control the electric field, preventing hot carriers from escaping into the oxide and maintaining a strong electric field in the multiplication region.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If photo carriers are accelerated in the multiplication region, then photocurrent gain is enhanced, but hot carrier injection into the oxide occurs causing degradation over time
Solution Approach 1:
A charge layer is introduced as an intermediary between the germanium absorption region and the silicon multiplication region. This charge layer mediates the electric field distribution, confining it primarily within the multiplication region while reducing field penetration into the oxide, thereby enabling high gain without excessive hot carrier injection degradation
Solution Approach 2:
The patent modifies the electric field distribution parameters by introducing a charge layer with specific doping concentrations and thicknesses. This changes the field profile to concentrate the high field in the multiplication region while reducing the field in the oxide, allowing sustained operation with maintained gain
2Area of moving object
If the multiplication region is made larger, then photocurrent gain is improved, but hot carrier scattering into the oxide increases
Solution Approach 1:
The charge layer creates locally differentiated electric field qualities: a strong confined field in the multiplication region for high gain, and a reduced field in the oxide region to minimize hot carrier injection. This local quality control allows large multiplication region area without proportionally increasing harmful HCl
3Force
If the electric field is strengthened in the multiplication region, then avalanche multiplication is enhanced, but hot carrier injection into the oxide is increased
Solution Approach 1:
The device is segmented into distinct functional regions with different electric field characteristics: the germanium absorption region with low field for carrier generation, the silicon multiplication region with high field for avalanche multiplication, and the oxide region with reduced field to prevent hot carrier injection. The charge layer acts as a boundary that enforces this segmentation
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 effectively reduces HCl degradation and allows for precise control of the charge layer, ensuring a strong electric field in the multiplication region, thereby enhancing the APD's ability to provide photocurrent gain and maintaining device performance over time.
Implementation Method 1
The multiplication region layer experiences a high field during operation as a result of the applied bias to the APD that splits between the Ge absorption region and the silicon multiplication region according to the device geometry and the extent and doping level of a charge layer
Implementation Method 2
The high field region in the multiplication region performs photocarrier multiplication by means of the avalanche effect. Photogenerated electrons injected from the absorption layer are accelerated in the multiplication region and create a secondary photocurrent due to impact ionization events
Implementation Method 3
Accelerated carriers in the multiplication region (either primary photo carriers or secondary carriers) are likely to be scattered and injected in the oxide (e.g., the BOX) surrounding the silicon multiplication region, which is called hot carrier injection (HCl)
Data Source
AI summary
Embodiments herein describe an APD architecture that includes a silicon cap layer formed on top of a germanium layer (e.g., a Ge absorption region). The silicon cap layer can form a multiplication region of the APD. Moreover, a charge layer can be formed between the absorption region and the silicon cap layer (e.g., the multiplication region).