Nickel diffusion into MoS₂ and the effect of annealing on contact resistance

Metal-semiconductor interfaces are crucial for the performance of many devices and understanding interactions between material interfaces after processing is therefore of interest. Here, field-effect transistors with Ni contacts are studied to determine the effects of annealing on contact resistance. Contact resistance and total resistance of as-deposited and annealed field-effect transistors with Ni/Ti/Au contacts increase upon annealing, with higher annealing temperatures yielding a greater increase in contact resistance. It appears that Ni diffusion into MoS₂ correlates with the observed higher contact resistance, and transmission electron microscopy, energy dispersive spectroscopy, and electron energy loss spectroscopy reveal the presence of Ni in single crystal MoS₂ flakes after annealing Ni/MoS₂ in ultra-high purity Ar gas at 400 °C. Metal diffusion into 2D semiconductors like MoS₂ may help or hurt device performance, and this work highlights the importance of considering the effects metal diffusion may have on contact resistance.