Semiconducting properties of zinc-doped cubic boron nitride thin films

We have examined the electronic properties of zinc-doped cubic boron nitride $(cBN)$ thin films prepared by sputter deposition. The electric conductivity of films deposited in pure Ar increased as the concentration of zinc dopant increased, and hole conduction was identified by the measurement of thermoelectric currents. It was also found that the conductivity increment in such films was accompanied by a linear increase in the $B∕(B+N)$ ratio. At the same time, no modification of the composition and the conductivity by incorporated zinc was observed when film growth took place in presence of nitrogen gas. The effect of the excess boron on the conductivity emerged only when films show semi-insulating behavior. These results suggest that Zn substitution for nitrogen causes high electric conductivity of $cBN$⁠. The electric contact between Ti electrode and semiconducting $cBN$ was examined by the transfer length method, and Ohmic conduction was observed in the $Ti∕cBN$ contact. The specific contact resistance was affected by the specific resistance of $cBN$ films, and it was reduced from $105to100Ωcm2$ by increasing the concentration of incorporated Zn.