Effect of boron doping on the electrical conduction of tetrahedral amorphous carbon films

Boron doped tetrahedral amorphous carbon films were prepared on a filtered cathodic vacuum arc deposition system by varying the weight percentage of boron in the mixed graphite cathodes. The electrical conductivity versus temperature, I- V characteristic and C-V characteristic for the films were measured by four-probe method, impedance/gain-phase analyzer, and electrochemical interface, respectively. As the boron content increases from 0 to 6.04 at %, the electrical conductivity of the films at room temperature increases gradually and then drops down, while the activation energy varies in the reverse. At the boron content of 2.13 at %, a maximum value of 1.42 × 10^-7 S/cm and a minimum value of 0.1 eV were obtained for the above two parameters, respectively. Furthermore, the rectification characteristics in the I-V curve indicated a p-n junction diode was formed for the boron doped tetrahedral amorphous carbon/n-type silicon heterojunction with uniform doping levels in the space at the two ends of the junction.