Distinguishing the Charge Trapping Centers in CaF 2 -Based 2D Material MOSFETs.

Crystalline calcium fluoride (CaF₂) is drawing significant attention due to its great potential of being the gate dielectric of two-dimensional (2D) material MOSFETs. It is deemed to be superior to boron nitride and traditional silicon dioxide (SiO₂) because of its larger dielectric constant, wider band gap, and lower defect density. Nevertheless, the CaF₂-based MOSFETs fabricated in the experiment still present notable reliability issues, and the underlying reason remains unclear. Here, we studied the various intrinsic defects and adsorbates in CaF₂/molybdenum disulfide (MoS₂) and CaF₂/molybdenum disilicon tetranitride (MoSi₂N₄) interface systems to reveal the most active charge-trapping centers in CaF₂-based 2D material MOSFETs. An elaborate Table comparing the importance of different defects in both n-type and p-type devices is provided. Most impressively, the oxygen molecules (O₂) adsorbed at the interface or surface, which are inevitable in experiments, are as active as the intrinsic defects in channel materials, and they can even change the MoSi₂N₄ to p-type spontaneously. These results mean that it is necessary to develop a high-vacuum packaging process, as well as prepare high-quality 2D materials for better device performance. [ABSTRACT FROM AUTHOR]