Stacked Amorphous and Crystalline Silicon Photosensor Efficiency
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Solution Overview
Problem
Liquid crystal display devices using amorphous or polysilicon semiconductor layers for photosensors face low photoelectric conversion efficiency due to limitations in material choice and manufacturing complexity, which restricts the performance of these sensors.
Innovation Solution
A stacked semiconductor layer structure combining an amorphous semiconductor layer and a crystalline semiconductor layer, such as polysilicon or microcrystalline silicon, is used to enhance photoelectric conversion efficiency by compensating for the defects of one layer with the other, allowing for improved electron-hole pair generation and separation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If amorphous silicon or polysilicon is used for the semiconductor layer, then the manufacturing process becomes simpler and cost-effective, but the photoelectric conversion efficiency becomes insufficient
Solution Approach 1:
The patent applies composite materials by stacking an amorphous semiconductor layer and a crystalline semiconductor layer to form a photosensor. The amorphous layer (made by PECVD) provides ease of manufacture and light absorption, while the crystalline layer (made by LPCVD) provides high photoelectric conversion efficiency. This composite structure resolves the contradiction between manufacturing simplicity and photoelectric efficiency.
Solution Approach 2:
The patent segments the semiconductor layer into two distinct layers with different functions: the amorphous semiconductor layer for light absorption and electron-hole pair generation, and the crystalline semiconductor layer for efficient charge separation and transport. This segmentation allows each layer to optimize its specific function while maintaining overall manufacturing feasibility.
2Reliability
If mono-crystalline silicon or GaAs is used for the semiconductor layer, then the photoelectric conversion efficiency is improved, but the manufacturing process becomes complicated and expensive
Solution Approach 1:
Instead of using expensive mono-crystalline silicon or GaAs throughout, the patent creates a composite structure where only a thin crystalline layer (providing high efficiency) is stacked on an amorphous layer (providing manufacturing ease). This achieves high photoelectric conversion efficiency while maintaining cost-effective manufacturing processes using standard semiconductor fabrication techniques.
Solution Approach 2:
The patent applies local quality by concentrating the high-performance crystalline semiconductor material only in the region where it is most needed for charge separation and transport, while using the cost-effective amorphous semiconductor material in the light absorption region. This localized application of different material qualities optimizes both performance and manufacturing cost.
3Ease of manufacture
If the semiconductor layer thickness is reduced to 50 nm for crystalline material, then the manufacturing process is simplified, but light with wavelength larger than 500 nm passes through and electron-hole pair generation decreases
Solution Approach 1:
The patent segments the light absorption and charge separation functions into two layers. The amorphous semiconductor layer (thicker, e.g., 100-500 nm) handles light absorption and electron-hole pair generation for wavelengths >500 nm, while the crystalline semiconductor layer (thin, ~50 nm) handles charge separation. This segmentation allows each layer to have optimized thickness for its specific function.
Solution Approach 2:
The amorphous semiconductor layer acts as an intermediary that absorbs light and generates electron-hole pairs, then transfers these carriers to the crystalline semiconductor layer for efficient separation. This intermediary layer enables the thin crystalline layer to function effectively without needing to be thick enough to absorb all the light itself.
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 significantly enhances the photoelectric conversion efficiency of the photosensors, enabling better detection of light and improving the overall performance of the display device without increasing manufacturing complexity.
Implementation Method 1
electron-hole pairs generated by incidence of light are separated from each other
Implementation Method 2
the photosensor is usually configured such that a reverse-directional voltage is applied to the diode structure having two terminals, and electron-hole pairs generated by incidence of light are separated from each other
Data Source
AI summary
A display device having a photosensor which exhibits excellent photoelectric conversion efficiency is provided. In a display device which forms photosensors on a substrate thereof, the photosensor is formed by sequentially stacking a gate electrode, a gate insulation film and a semiconductor layer in such an order or in an opposite order from a substrate side, and electrodes are connected to both sides of the semiconductor layer respectively, the semiconductor layer is formed of a stacked body consisting of a crystalline semiconductor layer and an amorphous semiconductor layer, and the crystalline semiconductor layer is arranged on the gate insulation film side.