Electrical characterization of homoepitaxial diamond films doped with B, P, Li and Na during crystal growth

Abstract

Abstract Using the microwave plasma CVD method, we have grown high-quality homoepitaxial diamond films on (100)-cut diamond substrates. The films were selectively grown as Hall bars by using a sputtered SiO2 mask on the diamond substrates. Electrical contacts were electron-beam evaporated Mo/Pt/Au layers which were annealed at high temperatures. Boron was mainly used as a p-type dopant, but lithium, sodium and phosphorus were also investigated as potential n-type dopants. Doping was done during film growth by placing the oxides of the different doping materials into the plasma chamber. The electrical conductivity as well as the current-voltage characteristics were measured over a large temperature range. In addition, Hall effect measurements were performed on boron-doped layers from 100 K to 1050 K. At room temperature the investigated Li-, Na- and P-doped films had very high resistivities over 109 Ωcm, undoped films even more than 1016 Ωcm. The activation energies of electrical resistivity were in the range 0–0.43 eV for boron and 0.16 eV for lithium. The undoped films grown on boron-doped substrates had breakdown fields up to 2 MV cm−1.