Lateral APD SAACM Structure Reducing Excess Noise
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Solution Overview
Problem
Avalanche photodiodes (APDs) in optical communication systems face challenges with excess noise, which reduces sensitivity and accuracy in signal detection, due to the stochastic process of impact ionization, and existing solutions are limited by material constraints and high electric fields that lead to dark current and reliability issues.
Innovation Solution
The proposed APD has a lateral structure with separate photon absorption, charge carrier acceleration, and charge carrier multiplication regions (SAACM structure), where charge carriers are first accelerated in the acceleration region and initiate impact ionization in the multiplication region, reducing randomness and excess noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If a conventional APD structure with separate absorption, charge, and multiplication regions is used, then gain is achieved through impact ionization, but excess noise increases due to the stochastic nature of the process
Solution Approach 1:
The device is divided into three distinct lateral regions: photon absorption region, charge carrier acceleration region, and charge carrier multiplication region. This segmentation allows each region to perform its specific function optimally, with the acceleration region preparing carriers through drift before they enter the multiplication region, thereby reducing the stochastic noise associated with conventional impact ionization processes.
Solution Approach 2:
The patent transitions from a vertical stacked structure to a lateral configuration where absorption, acceleration, and multiplication regions are arranged side-by-side in the same semiconductor layer. This dimensional change enables better control over carrier trajectories and reduces excess noise by separating the acceleration and multiplication processes spatially.
2Power
If high electric fields are applied to achieve impact ionization and gain, then multiplication is enhanced, but dark current increases and reliability decreases
Solution Approach 1:
High electric fields are confined specifically to the charge carrier acceleration region, while the multiplication region operates under different field conditions. This local differentiation allows the acceleration region to provide the necessary field strength for carrier preparation without subjecting the entire device to high fields that would generate dark current and reduce reliability.
Solution Approach 2:
Charge carriers are accelerated and prepared in the acceleration region before entering the multiplication region. This preliminary action of drift acceleration ensures carriers have sufficient energy and proper directionality before multiplication, reducing the need for excessively high fields in the multiplication region itself and thereby improving device reliability.
3Ease of manufacture
If material constraints are followed in conventional APD designs, then fabrication is simplified, but design flexibility and performance optimization are limited
Solution Approach 1:
The lateral SAACM structure can be implemented across different semiconductor material systems (e.g., Si, InP, InGaAs) without requiring fundamental design changes. The universal lateral configuration allows the same structural approach to be adapted to various materials, providing both manufacturing simplicity and design flexibility for different wavelength and performance requirements.
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 approach enhances sensitivity to optical signals, reduces dark current, and allows for the use of various semiconductor materials, making the APD more suitable for high-speed, low-energy optical communication systems with lower link power requirements.
Implementation Method 1
a photon absorption region disposed on the substrate
Implementation Method 2
charge carriers are first accelerated in the acceleration region
Implementation Method 3
charge carriers are first accelerated in the acceleration region and initiate impact ionization in the multiplication region
Data Source
AI summary
Examples described herein relate to an avalanche photodiode (APD) and an optical receiver including the APD. The APD may include a substrate and a photon absorption region disposed on the substrate. The substrate may include a charge carrier acceleration region under the photon absorption region; a charge region adjacent to the charge carrier acceleration region; and a charge carrier multiplication region adjacent to the charge region. The charge carrier acceleration region, the charge region, and the charge carrier multiplication region are laterally formed in the substrate. When a biasing voltage is applied to the optoelectronic device, photon-generated free charge carriers may be generated in the photon absorption region and are diffused into the charge carrier acceleration region. The charge carrier acceleration region is configured to accelerate the photon-generated free charge carriers prior to the photon-generated free charge carriers entering into the charge region and undergoing impact ionization in the charge carrier multiplication region.