Photodiode Intrinsic Layer Composition Gradient
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Solution Overview
Problem
The reduction in pixel size of image sensors with silicon photodiodes leads to decreased absorption area and sensitivity, prompting the consideration of organic semiconductors with higher extinction coefficients and wavelength selectivity, but these photodiodes often have undesirable external quantum efficiency and light responsivity.
Innovation Solution
A photodiode design featuring an intrinsic layer with varying composition ratios of P-type and N-type semiconductors, including sublayers with specific ratios of N,N′-dimethyl quinacridone and C60 or C70, and additional layers like electron and hole blocking layers, to enhance light absorption and charge generation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If pixel size is reduced to increase resolution, then image sensor resolution is improved, but absorption area and sensitivity decrease
Solution Approach 1:
The patent changes the material composition parameters within the intrinsic layer by varying the ratio of P-type to N-type semiconductor materials across different sublayers. This compositional parameter change enables enhanced light absorption and exciton generation efficiency in smaller pixel structures, allowing high resolution to be maintained without proportionally reducing sensitivity.
Solution Approach 2:
The patent employs a composite intrinsic layer structure combining P-type semiconductor (e.g., DMQA) and N-type semiconductor (e.g., C60, C70, PCBM) materials in specific ratios. This composite material approach creates synergistic effects that improve light absorption coefficients and charge generation efficiency, compensating for the reduced absorption area in miniaturized pixels.
2Illumination intensity
If organic semiconductors are used to increase extinction coefficient and wavelength selectivity, then light absorption capability is improved, but external quantum efficiency and light responsivity become undesirable
Solution Approach 1:
The patent applies local quality by creating sublayers with different P-type to N-type semiconductor material ratios at different positions within the intrinsic layer. The first sublayer (near anode) has a higher P-type ratio for efficient hole transport, while the second sublayer (near cathode) has a higher N-type ratio for efficient electron transport. This spatial variation in material composition optimizes both light absorption and charge carrier extraction, simultaneously improving extinction coefficient and external quantum efficiency.
3Reliability
If composition ratios of P-type and N-type semiconductors are varied within the intrinsic layer, then external quantum efficiency and light responsivity are improved, but device structure complexity increases
Solution Approach 1:
The patent segments the intrinsic layer into multiple sublayers (first sublayer, second sublayer, and optionally third sublayer), each with distinct P-type to N-type semiconductor material ratios. This segmentation allows independent optimization of charge transport properties in different regions while maintaining a relatively simple overall device architecture. The segmented structure achieves improved external quantum efficiency without requiring complete redesign of the entire photodiode 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 varying composition ratios and additional layers improve the external quantum efficiency and light responsivity of the photodiode, increasing its sensitivity and response time to incident light.
Implementation Method 1
The intrinsic layer absorbs light to produce excitons, and the excitons are divided into holes and electrons at a joint surface of the N-type semiconductor and the P-type semiconductor
Data Source
AI summary
A photodiode according to example embodiments includes an anode, a cathode, and an intrinsic layer between the anode and the cathode. The intrinsic layer includes a P-type semiconductor and an N-type semiconductor, and composition ratios of the P-type semiconductor and the N-type semiconductor vary within the intrinsic layer depending on a distance of the intrinsic layer from one of the anode and the cathode.