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Distinguishing the Charge Trapping Centers in CaF2-Based 2D Material MOSFETs
Zhe Zhao1,2, Tao Xiong2, Jian Gong1,3
1School of Physical Science and Technology, Inner Mongolia University, Hohhot 010021, China.
Nanomaterials (Basel, Switzerland)
|June 26, 2024
Summary
Crystalline calcium fluoride (CaF2) shows promise for 2D material MOSFETs but faces reliability issues. Oxygen adsorption is identified as a key factor causing these problems, necessitating vacuum packaging and high-quality material preparation.
Area of Science:
- Materials Science
- Semiconductor Physics
- Nanotechnology
Background:
- Crystalline calcium fluoride (CaF2) is a promising gate dielectric for 2D material MOSFETs, outperforming boron nitride and silicon dioxide (SiO2) due to its superior dielectric constant, wider band gap, and lower defect density.
- Despite its advantages, CaF2-based MOSFETs exhibit significant reliability issues, with the underlying causes not fully understood.
Purpose of the Study:
- To investigate intrinsic defects and adsorbates at CaF2/MoS2 and CaF2/MoSi2N4 interfaces.
- To identify the most active charge-trapping centers in CaF2-based 2D material MOSFETs.
- To elucidate the impact of adsorbates on device performance and type conversion.
Main Methods:
- First-principles calculations were employed to study defect and adsorbate behavior.
- Analysis focused on CaF2 interfaces with molybdenum disulfide (MoS2) and molybdenum disilicon tetranitride (MoSi2N4).
- Comparison of defect activity in n-type and p-type devices was performed.
Main Results:
- Intrinsic defects and adsorbed oxygen molecules (O2) were identified as significant charge-trapping centers.
- Adsorbed O2 molecules were found to be as active as intrinsic defects.
- Oxygen adsorption was shown to spontaneously convert MoSi2N4 to p-type.
Conclusions:
- Reliability issues in CaF2-based 2D MOSFETs are significantly influenced by adsorbed oxygen.
- High-vacuum packaging is crucial to mitigate the effects of oxygen adsorption.
- The preparation of high-quality 2D materials is essential for improved device performance.
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