UV Photodiode Trench Doping for Lower Reflection and Trapping
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Solution Overview
Problem
Photodiodes face reduced sensitivity due to increased interface length in effective media, which traps UV light-generated charge carriers, and existing methods do not adequately address reflection losses and durability issues, especially for UV light where penetration depth is low.
Innovation Solution
A method involving specific doping steps at different angles to form a photodiode with a graded refractive index effective medium, where the doping concentration along the interface decreases towards the pn-junction, reducing charge carrier trapping and enhancing UV sensitivity. This includes forming trenches filled with oxide and doping the sides and bottom of these trenches to push charge carriers away from the interface.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If an effective medium is used to reduce reflection losses, then reflection losses are reduced, but charge carrier trapping increases due to increased interface length
Solution Approach 1:
The effective medium is segmented into multiple discrete trenches filled with oxide material, rather than a continuous layer. This segmentation reduces the total interface length between the effective medium and the light-sensitive region, thereby reducing charge carrier trapping while maintaining the anti-reflection functionality through the distributed trench structure.
Solution Approach 2:
The doping concentration is varied locally along the interface, with higher doping concentrations near the trenches and lower concentrations towards the pn-junction. This local quality variation creates an electric field that repels charge carriers from the interface region, reducing trapping effects while preserving the effective medium's optical properties.
2Measurement precision
If UV light is used for detection, then sensitivity to UV light is improved, but penetration depth decreases causing higher charge carrier concentration near interface
Solution Approach 1:
The doping concentration is locally optimized with higher concentrations near the interface region where UV-generated charge carriers accumulate due to shallow penetration depth. This local doping enhancement creates an electric field that directs charge carriers away from trapping sites at the interface, improving UV detection sensitivity without suffering from interface trapping losses.
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 method significantly increases UV sensitivity and durability by reducing charge carrier trapping and reflection losses, allowing for improved detection of weaker UV signals with reduced noise and chip area requirements, while maintaining performance under UV light exposure.
Implementation Method 1
The high refractive index of the semiconductor material can cause a significant amount of light to be reflected before it enters the light sensitive region of the photodiode... The reflection losses can be reduced by creating a graded index using an effective medium by forming a layer comprising different proportions of materials having different refractive indices.
Implementation Method 2
A high doping concentration along the interface that steadily decreases towards the pn-junction pushes generated charge carriers away from the interface and towards the pn-junction (for detection).
Implementation Method 3
Photodiodes are used in a wide range of applications for detecting and measuring electromagnetic radiation.
Data Source
AI summary
A method of forming a photodiode including providing a semiconductor wafer and performing a first doping step to form a first well in the wafer having a first type of doping. The method further includes performing a second doping step to form a second well having a second type of doping, so as to form a pn-junction of the photodiode between the first well and the second well. The method includes performing a shallow trench isolation etch to form a plurality of trenches in a surface of the wafer in the second well, and performing a third doping step by injecting dopants at a first angle relative to the surface of the wafer in order to increase a doping concentration of the second type of doping along the sides of the trenches in the second well. The method includes performing a fourth doping step by injecting dopants at a second angle relative to the surface of the wafer in order to increase a doping concentration of the second type of doping at the bottom of the trenches in the second well. The method includes performing a fifth doping step to increase a doping concentration of the second type of doping at the surface of the semiconductor wafer between the trenches in the second well, and forming a first contact for contacting the first well and forming a second contact for contacting the second well in order to apply a voltage across the pn-junction when in use.