Multimodal Characterization of 2D Semiconductors Irradiated by High-Energy, High-Fluence Protons

Space science and exploration projects emphasize the need for electronics that are not only better at tolerating radiation for extended lifetime, but also have improved performance, and low energy consumption. 2D semiconductors can potentially outperform existing semiconductor technologies such as silicon for advanced microelectronics for space applications. 2D semiconductors are a-few-atom-thick materials with their body thickness less than 1 nm. Different from silicon, 2D semiconductors at such an extreme body thickness do not suffer from the unsaturated dangling bonds, surface roughness, and the associated carrier mobility degradation. Because of the further shrinkage of the body thickness, FETs made with sub-1-nm-thick 2D semiconductor channels also allow for the further downscaling of the gate lengths to sub-10-nm scale, a regime that no previous semiconductor technologies can achieve, with tremendous performance, power, and area benefits. Meanwhile, because of the same reason, the atomic-scale thickness gives rise to an ultra-small capture cross-section of ionizing radiation. As a result, transistors, memory devices, and integrated circuits made with 2D semiconductors are naturally more radiation tolerant than other semiconductor materials.
Previous investigations on radiation tolerance of low-dimensional semiconductors (such as 1D carbon nanotubes, 2D graphene, MoS₂, WS₂, etc.) have shown promising trends on the radiation hardness of these materials. However, the radiation conditions used in the previous studies are incomparable with the testing standards for radiation-hard electronics. In this work, we establish an experiment-simulation-combined framework to investigate radiation effects on monolayer MoS₂ with more application-relevant radiation conditions.
We investigated the displacement damage effects of 1-7 MeV range proton radiation on MoS₂, which covers the spectrum range of strongest interaction between protons and MoS₂ in the low-earth orbit (LEO) radiation conditions. Using comprehensive material characterization methods including Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and scanning transmission electron microscopy (STEM), different types of structural changes are quantified, including radiation-induced sulfur vacancies and the oxygen-passivated sulfur vacancies. The effect of oxygen passivation is associated with air exposure during radiation. In addition, through photoluminescence spectroscopy, Kelvin probe force microscopy (KPFM), and capacitive-voltage (C-V) measurements, we understood the impact of radiations on the electronic and optoelectronic properties of the MoS₂: sulfur vacancies cause n-type doping effect and oxygen passivation cause p-type doping effect; both of them contribute to charge impurities and degradation of mobilities. These characterization results indicate that monolayer MoS₂ does not undergo significant structural degradation with up to 10¹³ p/cm² fluence of 1-7 MeV proton radiation. We further performed Transport of ion in Matter (TRIM) simulation to compare proton radiation energy transfer and defect creation in MoS₂ and in silicon. We systematically investigated the influence of semiconductor body thickness, dielectric materials, and substrates on radiation tolerance and device performance, particularly as transistor dimensions continue to shrink. Our results highlight the advantages of 2D semiconductors over traditional silicon-based technologies, providing design guidelines for 2D semiconductor transistor technology that balances both downscaling potential and radiation hardness.