Quantum Dot Image Sensor Layers for Better Photocarrier Extraction
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Solution Overview
Problem
Quantum dot-based light-receiving devices face efficiency issues due to carrier recombination, which reduces the extraction of photocarriers generated in the quantum dot layer, leading to decreased performance in optoelectronic devices.
Innovation Solution
An optoelectronic device is designed with a structure comprising a first electrode, a second electrode, and an active layer with multiple quantum dot layers of different energy bands, including p-type and n-type layers, along with electron and hole transport layers, to enhance the extraction of photocarriers through a discontinuous energy band structure and controlled doping concentrations, thereby increasing external quantum efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a quantum dot layer is used as an absorption layer in a light-receiving device, then light absorption capability is improved, but carrier recombination occurs which reduces photocarrier extraction efficiency
Solution Approach 1:
The quantum dot absorption layer is divided into multiple sub-layers with different energy bands (first quantum dot layer with higher energy band, second quantum dot layer with lower energy band). This segmentation allows for staged photocarrier extraction, where high-energy photons generate carriers in the first layer and low-energy photons generate carriers in the second layer, reducing recombination losses and improving overall extraction efficiency.
Solution Approach 2:
Different regions of the quantum dot layer are assigned different energy band characteristics. The first quantum dot layer is optimized for high-energy photon absorption while the second layer is optimized for low-energy photon absorption. This local differentiation of energy band properties enables efficient photocarrier generation and extraction across the entire spectral range without significant recombination losses.
2Loss of energy
If multiple quantum dot layers with different energy bands are introduced, then photocarrier extraction efficiency is improved, but device structure complexity increases
Solution Approach 1:
Multiple quantum dot layers with different energy bands are merged into a single integrated absorption layer structure. This combined structure maintains the benefits of staged photocarrier extraction while simplifying the overall device architecture compared to using separate devices for different energy bands. The merged structure allows simultaneous operation of multiple energy band regions within one coherent layer.
3Speed
If doping concentration is increased to enhance charge extraction, then carrier mobility is improved, but carrier recombination increases
Solution Approach 1:
The energy band parameter is changed across different quantum dot layers to optimize charge extraction. The first quantum dot layer uses a higher energy band configuration that facilitates electron-hole separation, while the second layer uses a lower energy band configuration that promotes carrier extraction to respective electrodes. This parameter variation across layers enables efficient charge transport without requiring excessive doping concentrations that would increase recombination.
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 device achieves an external quantum efficiency of 25% or higher, improving the transfer efficiency of photocarriers and enhancing the overall performance of optoelectronic devices by effectively utilizing the quantum dot layers.
Implementation Method 1
when the quantum dots absorb light energy, a photocarrier is generated in the quantum dot layer
Implementation Method 2
Colloidal quantum dots exhibit different band gaps depending on their sizes due to the quantum confinement effect at the nano size
Data Source
AI summary
Provided is an image sensor including a sensor array including a plurality of light-sensors respectively including an optoelectronic device, the optoelectronic device including a first electrode, a second electrode spaced apart from the first electrode, and an active layer provided between the first electrode and the second electrode, the active layer including a plurality of quantum dot layers having different energy bands, and a circuit including circuits respectively connected to the plurality of light-sensors and configured to readout an optoelectronic signal generated from each of the plurality of light-sensors.