A New Strategy to Develop p-Type Semiconductivity in Transition Metal Dichalcogenides: A First-Principles Study

Over the years, silicon has been the preferred choice of channel material in transistors due to its simplicity and scalability. However, the performance of Si-based transistors degrades significantly as the channel thickness is reduced below 4 nm [1]. TMDs with group formula MX₂, where M = Mo, W and X = S, Se are a class of two-dimensional (2D) semiconductors that can replace Si in the next-generation transistors. Recently, it was shown that the mobility of monolayer TMDs are comparable with 4 nm thick Si channels [1]. Therefore, integrating TMDs into existing hyper-scaler geometries has the potential to leapfrogging decades on Moore's law time scale [2]. However, strategies to p-dope TMDs have been largely unsuccessful. Conventional approaches like substitution doping creates inhomogeneity such as charged defects within the channel layer that limits the transistor mobility [3].<br/><br/>In this talk, we propose a new strategy to p-dope TMDs via a surface charge transfer mechanism (SCTM) using inorganic oxides. Using physics based HT screening we identify 11 element that when doped into the high-k dielectric oxide layer (e.g. HfO₂) can p-dope TMDs without creating channel defects. To validate these finding, we demonstrate p-doping of WSe₂using Ni-doped HfO₂using first-principles density functional theory (DFT) calculation. We also discuss practical device geometries for implementing this SCTM induced doping and strategies to control the concentration of dopants. Thus our holistic approach proves the feasibility of p-dope TMDs while retaining the advantages of having a high-k gate-dielectric layer. Demonstrating p-doping in atomically-thin TMDs can allow us to save decades in Moore’s law scaling, and can usher in the post-Si era for transistors. This approach can be easily generalized to tackle a broad array of materials design challenges. Our results provide a new strategy for p-doping TMDs.<br/><br/>[1] S. Su et al., Layered Semiconducting 2D Materials for Future Transistor Applications. <i>Small Struct.</i>, 2: 2000103, 2021.<br/>[2] S. Datta et al., Toward attojoule switching energy in logic transistors. <i>Science</i>, 378.6621, 733, 2022.<br/>[3] Z. Hu et al., Two-dimensional transition metal dichalcogenides: interface and defect engineering. <i>Chemical Society Reviews</i>, 47, 3100, 2018.