Quantum Dot Photodetectors Monolithic Silicon Integration
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Solution Overview
Problem
Current short-wavelength infrared (SWIR) photodetection and imaging systems using epitaxial compound semiconductors or chemical bath-grown polycrystalline materials are incompatible with silicon integrated circuit fabrication, leading to complex assembly, low yield, poor resolution, and high cost, while quantum dot-based systems have relatively low gains and sensitivities.
Innovation Solution
A method of sensitizing silicon CCD or CMOS focal plane arrays using spin-coated quantum dot nanocrystals and semiconducting polymers to create efficient, high-detectivity photodetectors that can be integrated monolithically with the read-out circuit, enabling low-cost, high-sensitivity imaging systems for various applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If epitaxial compound semiconductors or chemical bath-grown polycrystalline materials are used for SWIR photodetection, then high sensitivity and detectivity are achieved, but compatibility with silicon integrated circuit fabrication is lost, leading to complex assembly and high cost
Solution Approach 1:
The patent changes the material parameters by using quantum dots with specific bandgap energies that match silicon substrate properties, enabling lattice matching and thermal compatibility. This allows the optically sensitive layer to be fabricated using standard silicon CMOS processes rather than requiring separate epitaxial growth facilities, thereby reducing assembly complexity while maintaining high detectivity
Solution Approach 2:
The patent creates a composite structure by integrating quantum dot nanocrystals with silicon substrates. The quantum dots serve as the optically sensitive layer while the silicon provides the integrated circuit platform. This composite approach enables monolithic integration of the photodetector with the readout circuit, eliminating complex assembly of separate components while achieving high sensitivity through the quantum dot material properties
2Device complexity
If quantum dots are used as photosensitive material, then compatibility with silicon integrated circuits is improved, but gain and sensitivity are reduced
Solution Approach 1:
The patent applies local quality by creating a layered structure where quantum dots are positioned specifically at the interface between the silicon substrate and the optical path. The quantum dot layer is optimized for light absorption in its specific region, while the underlying silicon bulk provides carrier collection and circuit functionality. This spatial differentiation allows each material to operate in its optimal regime, achieving both compatibility and sensitivity
Solution Approach 2:
The patent uses quantum dots as an intermediary layer between the silicon substrate and incident light. The quantum dots absorb photons and generate carriers that are then transferred to the silicon for collection by the readout circuit. This intermediary function allows the system to benefit from the optical properties of quantum dots while maintaining the electrical advantages of silicon, achieving both compatibility and high sensitivity through the mediating role of the quantum dot layer
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 enables the production of photodetectors with improved noise equivalent exposure and responsivity, suitable for low-light imaging and other applications, with the potential for low-cost infrared imaging systems for security and missile tracking.
Implementation Method 1
The QD layer 38 is optically active and sensitive to electromagnetic radiation in the visible and infrared portions of the electromagnetic spectrum
Implementation Method 2
The invention provides a method of sensitizing a pre-fabricated focal plane array sensitive into the visible and infrared spectral ranges using spin-coated quantum dot nanocrystals
Data Source
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AI summary
Optical and optoelectronic devices and methods of making same. Under one aspect, an optical device includes an integrated circuit an array of conductive regions; and an optically sensitive material over at least a portion of the integrated circuit and in electrical communication with at least one conductive region of the array of conductive regions. Under another aspect, a method of forming a nanocrystalline film includes fabricating a plurality of nanocrystals having a plurality of first ligands attached to their outer surfaces; exchanging the first ligands for second ligands of different chemical composition than the first ligands; forming a film of the ligand- exchanged nanocrystals; removing the second ligands; and fusing the cores of adjacent nanocrystals in the film to form an electrical network of fused nanocrystals. Under another aspect, a film includes a network of fused nanocrystals, the nanocrystals having a core and an outer surface, wherein the core of at least a portion of the fused nanocrystals is in direct physical contact and electrical communication with the core of at least one adjacent fused nanocrystal, and wherein the film has substantially no defect states in the regions where the cores of the nanocrystals are fused.