SOI P-N Junction Diode for Terahertz Detection
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Solution Overview
Problem
High-frequency detectors based on p-n junction diodes face limitations due to effective path length for carrier diffusion and series resistance, which restrict their operation frequency and signal-to-noise ratio.
Innovation Solution
A novel diode structure is fabricated using a silicon-on-insulator (SOI) substrate, where a p-n junction diode is formed with doped regions and a back contact, reducing effective diffusion capacitance and series resistance by optimizing the diode's design and fabrication process, including the use of epitaxial growth and selective etching techniques.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If conventional p-n junction diode structure is used, then device simplicity is maintained, but effective path length for carrier diffusion and series resistance limit operation frequency
Solution Approach 1:
The diode structure is segmented into distinct regions including a first doped region, a second doped region with different conductivity type, and a third doped region. This segmentation allows optimization of carrier diffusion paths and reduction of series resistance by creating specialized zones for different functions, thereby enabling higher operation frequencies while managing structural complexity through modular design
Solution Approach 2:
Different regions of the diode are doped with different doping concentrations and conductivity types to create local variations in electrical properties. The first doped region has a first doping concentration, the second doped region has a second doping concentration, and the third doped region has a third doping concentration. This local quality optimization reduces effective series resistance and controls carrier diffusion paths, improving operation frequency
2Speed
If effective path length for carrier diffusion is reduced, then operation frequency increases, but manufacturing precision requirements increase
Solution Approach 1:
The carrier substrate is removed in advance to expose the insulator layer before forming the doped regions. This preliminary action allows subsequent doped regions to be formed with precise control over their depth and positioning, as the insulator layer serves as a defined boundary and stopping layer during doping processes, thereby enabling reduced carrier diffusion path length with manageable manufacturing precision
Solution Approach 2:
The insulator layer acts as an intermediary element between the carrier substrate and the active device layer. By removing the carrier substrate and exposing the insulator layer, the insulator serves as a reference plane and electrical isolation barrier, enabling precise formation of doped regions with controlled depths and positions, thus facilitating reduced carrier diffusion paths while maintaining manufacturability
3Reliability
If effective series resistance is reduced, then signal-to-noise ratio improves, but device complexity increases
Solution Approach 1:
Multiple doped regions with different conductivity types are merged into a single integrated diode structure. The first doped region, second doped region, and third doped region are combined to form a unified device that achieves low series resistance through optimized current paths while maintaining a compact structure, thereby improving signal-to-noise ratio without excessive complexity increase
Solution Approach 2:
The doping concentrations are optimized with specific parameter values: the first doped region has a first doping concentration, the second doped region has a second doping concentration, and the third doped region has a third doping concentration. By carefully selecting and varying these doping parameters, the effective series resistance is reduced to improve signal-to-noise ratio while controlling the complexity of the device structure
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 novel diode structure significantly enhances the signal-to-noise ratio and mechanical flexibility, allowing for higher operation frequencies while maintaining low noise performance.
Implementation Method 1
high-frequency (e.g., terahertz (THz)) detectors based on p-n junction diodes
Implementation Method 2
an effective path length for carrier diffusion
Data Source
AI summary
A method of forming a semiconductor detector including: forming a p-n junction diode in an active device layer of a silicon-on-insulator (SOI) substrate, the active device layer being formed on an insulator layer of the SOI substrate; forming a first opening through the insulator layer to access a backside of a first doped region of the diode, the first doped region underlying a second doped region of the diode; forming a back contact on a back surface of the first doped region and electrically connecting with the first doped region; forming a conductive interconnect layer on an upper surface of the SOI substrate, the interconnect layer including a first top contact providing electrical connection with the second doped region; and forming an electrode in the first opening on the backside of the detector structure, the electrode providing electrical connection with the back contact of the diode.