Quantum Dot Photoconductor for Infrared Light Absorption
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Solution Overview
Problem
Silicon photodiodes have low light absorption, particularly in the infrared band, limiting their application in sensitive night filming, 3D cameras, movement sensors, iris recognition sensors, and thermal image sensors due to increased optical/electric interference and decreased light absorption at smaller pixel sizes.
Innovation Solution
A photoconductor with a type II or quasi-type-II junction structure formed by quantum dot materials, including nanocrystals of Group IV, II-VI, III-V, III2-VI3, I-III-VI2, and I2-II-IV-VI4 semiconductors, coated with ligands, which enhances light absorption and separation of electron/hole pairs, improving reaction speed and sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If silicon photodiode is used for light absorption in image sensor, then high reliability and compatibility with logic device are achieved, but light absorption is too low especially in infrared band
Solution Approach 1:
The patent employs a composite material structure consisting of a silicon substrate combined with a quantum dot layer. The quantum dot layer is formed by depositing semiconductor nanocrystals (such as PbS, PbSe, or InAs) onto the silicon substrate, creating a hybrid structure that combines the high reliability of silicon with the superior infrared light absorption of quantum dots. This composite approach allows the device to maintain silicon's stability and compatibility while adding quantum dot's enhanced optical properties.
Solution Approach 2:
The patent changes the material parameters by introducing quantum dots with specific bandgap energies that are optimized for infrared absorption. By selecting quantum dot materials with appropriate bandgap values (e.g., PbS with 0.41 eV, PbSe with 0.27 eV), the device can absorb infrared wavelengths that silicon cannot effectively detect, thereby extending the spectral response into the infrared region while maintaining overall device reliability.
2Device complexity
If pixel size is reduced to below 1 μm to increase integration, then device complexity is reduced, but optical/electric interference increases and light absorption decreases
Solution Approach 1:
The quantum dot-silicon composite structure enables enhanced light absorption in reduced pixel sizes by utilizing the quantum dot layer's high absorption coefficient. The quantum dots act as efficient light traps that can absorb photons even in thin layers, compensating for the reduced pixel area and maintaining sufficient signal generation despite smaller dimensions.
3Illumination intensity
If photoconductor with quantum dot is used to achieve high sensitivity, then light absorption is improved, but reaction speed becomes slow due to persistent photoconductivity
Solution Approach 1:
The patent utilizes the composite structure of quantum dot layer on silicon substrate to balance sensitivity and response speed. The silicon substrate provides fast carrier collection and low dark current characteristics, while the quantum dot layer contributes high light absorption. This combination mitigates the persistent photoconductivity issue by allowing rapid carrier extraction through the silicon, reducing residual current effects while maintaining high sensitivity during illumination.
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 photoconductor achieves a high photoelectric conversion rate and fast reaction speed, enabling improved light absorption and sensitivity across a wide IR and mid-IR range, overcoming the limitations of silicon photodiodes in current image sensors.
Implementation Method 1
a photoconductor includes a first semiconductor layer, a second semiconductor layer disposed on the first semiconductor layer... the first semiconductor layer and the second semiconductor layer form a type II junction or a quasi-type-II junction
Implementation Method 2
the first semiconductor layer and the second semiconductor layer form a type II junction or a quasi-type-II junction
Data Source
AI summary
A photoconductor includes a first semiconductor layer, a second semiconductor layer disposed on the first semiconductor layer, a first electrode connected to a first lateral side of the first semiconductor layer and the second semiconductor layer, and a second electrode connected to a second lateral side of the first semiconductor layer and the second semiconductor layer, where the first semiconductor layer and the second semiconductor layer form a type II junction or a quasi-type-II junction.