Among two-dimensional (2D) transition metal dichalcogenides (TMDs), platinum diselenide (PtSe2) stands at a unique place in the sense that it undergoes a phase transition from type-II Dirac semimetal to indirect-gap semiconductor as thickness decreases. Defects in 2D TMDs are ubiquitous and play crucial roles in understanding and tuning electronic, optical, and magnetic properties. Here we investigate intrinsic point defects in ultrathin 1T-PtSe2 layers grown on mica through the chemical vapor transport (CVT) method, using scanning tunneling microscopy and spectroscopy (STM/STS) and first-principles calculations. We observed five types of distinct defects from STM topography images and obtained the local density of states of the defects. By combining the STM results with the first-principles calculations, we identified the types and characteristics of these defects, which are Pt vacancies at the topmost and next monolayers, Se vacancies in the topmost monolayer, and Se antisites at Pt sites within the topmost monolayer. Our study shows that the Se antisite defects are the most abundant with the lowest formation energy in a Se-rich growth condition, in contrast to cases of 2D molybdenum disulfide (MoS2) family. Our findings would provide critical insight into tuning of carrier mobility, charge carrier relaxation, and electron-hole recombination rates by defect engineering or varying growth condition in few-layer 1T-PtSe2 and other related 2D materials.
Towards Intrinsic Charge Transport in Monolayer Molybdenum Disulfide by Defect and Interface Engineering
二硫化钼被认为是一种在电子和光电子器件应用中最有前途的二维半导体材料。到目前为止，单层二硫化钼中的电荷输运是由外部因素，如带电杂质，结构缺陷和陷阱，导致迁移率远低于本征极限。在这里，我们开发了一种简单的低温硫醇化学来修复硫空位并改善界面，从而显著减少带电杂质和陷阱。室温下背栅单层二硫化钼场效应晶体管的迁移率大于80 cm ~ 2 V ~（-1）s ~（-1）。此外，我们开发了一个理论模型，以定量提取控制晶体管性能的关键微观量，包括带电杂质，短程缺陷和陷阱的密度。我们的实验和理论研究相结合，提供了一个明确的路径，本征电荷输运在二维dichalcogenides为未来的高性能器件的应用。
