Semiconducting few-layer PdSe2 and Pd2Se3: native point defects and contacts with native metallic Pd17Se15

Abstract

PdSe₂ is a unique layered two-dimensional (2D) material with pentagonal structural motif and anisotropic properties. In addition, its strong interlayer interaction leads to new 2D form of the exfoliated monolayer, that is, Pd₂Se₃. Despite the increasing interest in these emerging 2D materials, the landscape of the native point defects, as a fundamental materials property, has not been revealed. In this work, we systematically investigate different types of defects in mono- and bi-layer PdSe₂ and monolayer Pd₂Se₃. In contrast to the common expectation, Se vacancy is not the readily formed defect. Instead, Se-excess defects, such as Se_Pd antisite and Se interstitial, are more likely to form over a majority of the allowed range of the atomic chemical potentials. Se-deficiency defect, Pd interstitial, is able to form under the Se-poor condition in bilayer PdSe₂. The defect-mediated interlayer fusion model in the formation of monolayer Pd₂Se₃ from bilayer PdSe₂ is reformulated. These dominant defects are found to stay in the neutral charge state, partly explaining the ambipolar behavior of the PdSe₂ transistors. Finally, the stacked and lateral contacts between these few-layer semiconductors and the native Pd₁₇Se₁₅ metal are also studied. All these interfaces show p-type contact properties. This work reveals the important materials properties of few-layer PdSe₂ and Pd₂Se₃ for the better development of new functional devices.