Solid-state formation of titanium carbide and molybdenum carbide as contacts for carbon-containing semiconductors

Metal carbides are good candidates to contact carbon-based semiconductors (SiC, diamond, and carbon nanotubes). Here, we report on an in situ study of carbide formation during the solid-state reaction between thin Ti or Mo films and C substrates. Titanium carbide (TiC) was previously reported as a contact material to diamond and carbon nanotubes. However, the present study shows two disadvantages for the solid-state reaction of Ti and C. First, because Ti reacts readily with oxygen, a capping layer should be included to enable carbide formation. Second, the TiC phase can exist over a wide range of composition (about 10%, i.e., from Ti 0.5C 0.5 to Ti 0.6C 0.4), leading to significant variations in the properties of the material formed. The study of the Mo-C system suggests that molybdenum carbide (Mo 2C) is a promising alternative, since the phase shows a lower resistivity (about 45% lower than for TiC), the carbide forms below 900 °C, and its formation is less sensitive to oxidation as compared with the Ti-C system. The measured resistivity for Mo 2C is ρ =59 μω cm, and from kinetic studies an activation energy for Mo 2C formation of Ea =3.15±0.15 eV was obtained. © 2006 American Institute of Physics.