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

Abstract

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 ${\mathrm{Ti}}_{0.5}{\mathrm{C}}_{0.5}$ to ${\mathrm{Ti}}_{0.6}{\mathrm{C}}_{0.4}$ ), leading to significant variations in the properties of the material formed. The study of the Mo–C system suggests that molybdenum carbide $\left({\mathrm{Mo}}_2\mathrm{C}\right)$ is a promising alternative, since the phase shows a lower resistivity (about 45% lower than for TiC), the carbide forms below $900°\mathrm{C}$ , and its formation is less sensitive to oxidation as compared with the Ti–C system. The measured resistivity for ${\mathrm{Mo}}_2\mathrm{C}$ is $\rho =59\mu \Omega \mathrm{cm}$ , and from kinetic studies an activation energy for ${\mathrm{Mo}}_2\mathrm{C}$ formation of $E_a=3.15\pm 0.15\mathrm{eV}$ was obtained.