Influence of High‑κ\nDielectrics Integration\non ALD-Based MoS<sub>2</sub> Field-Effect Transistor Performance

The integration of high-κ dielectrics on MoS<sub>2</sub> field-effect\ntransistors (FETs) is essential for the realization of MoS<sub>2</sub> in ultrascaled nanoelectronic devices and circuits. Most studies\ncovering this topic are based on exfoliated MoS<sub>2</sub> flakes\nor chemical vapor deposition (CVD) grown MoS<sub>2</sub> films, whereas\nother techniques, such as atomic layer deposition (ALD), are also\ngaining attention for the growth of MoS<sub>2</sub> in recent years.\nIn this work, we grow large-area MoS<sub>2</sub> by means of plasma-enhanced\n(PE-)ALD and evaluate the influence of high-κ dielectrics on\nthe properties of ALD-based MoS<sub>2</sub> FETs through electrical\ncharacterization combined with surface-chemical and high-resolution\nscanning transmission electron microscopy (HR-STEM) analyses. We grow\nHfO<sub><i>x</i></sub>, AlO<sub><i>x</i></sub>, or both by means of PE-ALD or thermal ALD on our fabricated devices\nand show that, in addition to the dielectric constant, three other\nmajor parameters related to the processing of the dielectrics can\nsimultaneously affect the MoS<sub>2</sub> FET electrical characteristics\nand govern its doping. These parameters are the stoichiometry of the\ndielectric, its carbon impurity content, and the degree to which the\nMoS<sub>2</sub> surface oxidizes upon the dielectric growth. When\ngrown at 100 °C, our HfO<sub><i>x</i></sub> films are\noxygen-vacant whereas our AlO<sub><i>x</i></sub> films are\noxygen-rich. In addition, carbon impurities are incorporated into\nthe dielectrics at low deposition temperatures, being one of the likely\ncauses of the MoS<sub>2</sub> FET overall <i>n</i>-type\nperformance in all of the studied cases. Our investigations also reveal\nthat PE-ALD of HfO<sub><i>x</i></sub> or AlO<sub><i>x</i></sub> oxidizes the MoS<sub>2</sub> surface, whereas thermal\nALD AlO<sub><i>x</i></sub> leaves MoS<sub>2</sub> almost\nintact. In this respect, if thermal ALD AlO<sub><i>x</i></sub> of proper thickness is grown between MoS<sub>2</sub> and\nHfO<sub><i>x</i></sub>, it can reduce the degree to which\nthe MoS<sub>2</sub> surface oxidizes by HfO<sub><i>x</i></sub> and meanwhile improve the total dielectric constant, altogether\nleading to the most optimal electrical performance in ALD-based MoS<sub>2</sub> FETs.