nBn Photodetector Barrier Layer Reduces Dark Current
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Solution Overview
Problem
Existing thermal imaging devices using infra-red detectors require cryogenic cooling, are costly, and suffer from high dark noise due to the presence of depletion layers, which limits their performance and operational temperature.
Innovation Solution
A photo-detector design featuring a photo-absorbing layer with a barrier layer that prevents tunneling of majority carriers and thermalized carriers, eliminating the need for a depletion layer and reducing dark current, allowing operation at higher temperatures without passivation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If cryogenic cooling is used to reduce dark current, then dark current is reduced, but device complexity and cost increase
Solution Approach 1:
The invention extracts and eliminates the depletion layer from the photodetector structure, which is the primary source of dark current generation through Shockley-Reed-Hall processes. By removing this problematic region entirely and using a barrier layer instead, the design eliminates the need for cryogenic cooling systems while maintaining low dark current performance.
Solution Approach 2:
The invention changes the operational temperature parameter from cryogenic ranges (requiring complex cooling) to higher temperatures (reducing cooling requirements). This is achieved by modifying the semiconductor structure to prevent thermal generation of carriers that would otherwise require low-temperature operation to suppress.
2Reliability
If depletion layer is used to detect carriers, then carrier detection is enabled, but dark noise increases
Solution Approach 1:
The invention introduces a barrier layer as an intermediary between the absorbing layer and contact layer. This barrier layer mediates carrier transport by allowing photogenerated carriers to pass while blocking thermalized majority carriers, thereby enabling carrier detection without the dark noise problems associated with depletion layers.
Solution Approach 2:
The invention converts the harmful effect of thermal carrier generation into a beneficial filtering mechanism. The barrier layer exploits the energy difference between photogenerated carriers and thermalized carriers to selectively transmit useful signals while blocking noise, turning what would be a source of dark current into a filtering advantage.
3Object-generated harmful factors
If cooling system is added to reduce dark current, then dark current is reduced, but weight and power consumption increase
Solution Approach 1:
The invention extracts and removes the entire cryogenic cooling subsystem from the detector assembly. By eliminating the cooling requirement through structural modification (removing the depletion layer), the design reduces weight by removing heavy cooling components while maintaining low dark current performance.
4Object-generated harmful factors
If cryogenic temperatures are used to reduce dark current, then dark current is reduced, but manufacturing cost increases
Solution Approach 1:
The invention extracts and eliminates the need for expensive cryogenic cooling infrastructure. By redesigning the detector to operate without depletion layers and without cryogenic cooling, the manufacturing cost is reduced while maintaining low dark current through the barrier layer 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 solution significantly reduces dark current, enabling thermal imaging devices to operate at higher temperatures, reducing power consumption, weight, and production costs while extending operational duration.
Implementation Method 1
Examples of these existing technologies are presented in FIG. 5A to FIG. 5F. The cryogenic temperatures primarily are used to reduce the dark current generated in the p-n junction diode
Data Source
AI summary
A IDCA system combining thermo-electric cooler (TEC) and an internal nBn photo-detector having a photo absorbing layer comprising an n-doped semiconductor exhibiting a valence band energy level; and a contact layer comprising a doped semiconductor. A barrier layer is disposed between the photo absorbing layer and the contact layer, the barrier layer exhibiting a valence band energy level substantially equal to the valence band energy level of the doped semiconductor of the photo absorbing layer; the barrier layer exhibiting a thickness and a conductance band gap sufficient to prevent tunneling of majority carriers from the photo absorbing layer to the contact area and block the flow of thermalized majority carriers from the photo absorbing layer to the contact area. Alternatively, a p-doped semiconductor is utilized, and conductance band energy levels of the barrier and photo absorbing layers are equalized.