Photosensitive FET With Work Function Gradient Semiconducting Layer
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Solution Overview
Problem
The existing photosensitive field-effect transistors using graphene and semiconducting photoactive materials face challenges in achieving optimal carrier multiplication and spectral response, particularly at long infrared wavelengths due to unfavorable energetics at the interface between graphene and the photoactive layer, leading to inefficient charge trapping and recombination.
Innovation Solution
A semiconducting layer comprising vertically stacked assemblies of semiconducting materials with different work functions is introduced, creating a built-in electric field that funnels charge carriers to the transistor channel, enhancing charge multiplication and spectral response by optimizing the work function gradient based on the properties of the two-dimensional channel material.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single semiconducting photoactive layer is used, then the device structure is simple, but the carrier multiplication effect is insufficient and spectral response is limited
Solution Approach 1:
The photoactive layer is segmented into multiple semiconducting layers with different bandgaps arranged in a specific order. Each layer absorbs different wavelength ranges of electromagnetic radiation, creating multiple interfaces that enhance carrier multiplication effects and broaden spectral response while maintaining manageable structural complexity
Solution Approach 2:
The patent uses composite semiconducting materials with different bandgap energies (e.g., PbS, PbSe, PbTe) to create a multi-layer photoactive structure. This composite approach enables simultaneous optimization of carrier multiplication across different spectral regions, resolving the contradiction between structural simplicity and detection effectiveness
2Adaptability or versatility
If the bandgap of the semiconducting photoactive material corresponds to long infrared wavelengths, then the spectral response extends to longer wavelengths, but the built-in electric field strength is reduced leading to inefficient charge trapping
Solution Approach 1:
Different semiconducting layers are assigned different local properties (bandgap energies) to optimize their function: layers with smaller bandgaps absorb long-wavelength infrared radiation while layers with larger bandgaps provide stronger built-in electric fields for efficient charge trapping. This local optimization resolves the contradiction between spectral range and trapping efficiency
Solution Approach 2:
The patent systematically varies the bandgap parameter across multiple semiconducting layers to create a gradient structure. By changing the bandgap parameter from layer to layer, the device achieves both extended spectral response and maintained charge trapping efficiency through optimized parameter distribution
3Reliability
If multiple semiconducting layers with different work functions are stacked, then the built-in electric field is enhanced improving carrier funneling, but the device structure and manufacturing complexity increase
Solution Approach 1:
The complex multi-layer structure is segmented into discrete semiconducting layers with specific work function values, allowing systematic optimization of carrier funneling while managing manufacturing complexity through modular layer design
Solution Approach 2:
The work function parameter is systematically varied across the semiconducting layers to create an optimized gradient for carrier funneling. This parameter-based design approach allows prediction and optimization of electric field distribution, reducing the trial-and-error complexity in device fabrication
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 configuration improves the electrical and optical properties of the photoactive layer, leading to increased sensitivity and efficiency in detecting electromagnetic radiation across a broader wavelength range, including long infrared wavelengths, by effectively trapping minority carriers and funneling majority carriers into the graphene channel.
Implementation Method 1
A graphene field-effect transistor (GFET), for example, comprises a semiconducting graphene channel whose conductivity increases when it is illuminated by electromagnetic radiation
Implementation Method 2
A built-in electric field (electrostatic potential) may be formed between the photoactive layer and the graphene layer in thermodynamic equilibrium. It may facilitate trapping of minority carriers when electromagnetic radiation illuminates the photoactive material
Implementation Method 3
This increased conductivity can be measured, and strongly amplified, in a field-effect transistor geometry where the current through the channel is controlled by a gate voltage applied to an electrode adjacent to the channel
Data Source
Figure 1a~1c
Figure 1d~1e
Figure 1f
AI summary
A photosensitive field-effect transistor configured to provide an electrical response when illuminated by electromagnetic radiation incident on the transistor. The photosensitive field-effect transistor comprises a layer of two-dimensional material which forms a horizontal transistor channel configured to transport current, and a horizontal semiconducting layer in contact with the transistor channel. The semiconducting layer comprises two or more assemblies of semiconducting material. If the two-dimensional material in the transistor channel has a high work function, the assemblies of semiconducting material are vertically stacked on the transistor channel in order of decreasing work function. If the two-dimensional material in the transistor channel has a low work function, the assemblies of semiconducting material are vertically stacked on the transistor channel in order of increasing work function. The semiconducting materials may, for example, comprise semiconductor nanocrystals, quantum dots or thin-film semiconducting layers.