Influence of High-κ Dielectrics Integration on ALD-Based MoS₂ Field-Effect Transistor Performance

The integration of high-κ dielectrics on MoS₂ field-effect transistors (FETs) is essential for the realization of MoS₂ in ultrascaled nanoelectronic devices and circuits. Most studies covering this topic are based on exfoliated MoS₂ flakes or chemical vapor deposition (CVD) grown MoS₂ films, whereas other techniques, such as atomic layer deposition (ALD), are also gaining attention for the growth of MoS₂ in recent years. In this work, we grow large-area MoS₂ by means of plasma-enhanced (PE-)ALD and evaluate the influence of high-κ dielectrics on the properties of ALD-based MoS₂ FETs through electrical characterization combined with surface-chemical and high-resolution scanning transmission electron microscopy (HR-STEM) analyses. We grow HfO _<i>x</i> , AlO _<i>x</i> , or both by means of PE-ALD or thermal ALD on our fabricated devices and show that, in addition to the dielectric constant, three other major parameters related to the processing of the dielectrics can simultaneously affect the MoS₂ FET electrical characteristics and govern its doping. These parameters are the stoichiometry of the dielectric, its carbon impurity content, and the degree to which the MoS₂ surface oxidizes upon the dielectric growth. When grown at 100 °C, our HfO _<i>x</i> films are oxygen-vacant whereas our AlO _<i>x</i> films are oxygen-rich. In addition, carbon impurities are incorporated into the dielectrics at low deposition temperatures, being one of the likely causes of the MoS₂ FET overall <i>n</i>-type performance in all of the studied cases. Our investigations also reveal that PE-ALD of HfO _<i>x</i> or AlO _<i>x</i> oxidizes the MoS₂ surface, whereas thermal ALD AlO _<i>x</i> leaves MoS₂ almost intact. In this respect, if thermal ALD AlO _<i>x</i> of proper thickness is grown between MoS₂ and HfO _<i>x</i> , it can reduce the degree to which the MoS₂ surface oxidizes by HfO _<i>x</i> and meanwhile improve the total dielectric constant, altogether leading to the most optimal electrical performance in ALD-based MoS₂ FETs.