ELECTRICAL CHARACTERIZATION OF HOMOEPITAXIAL DIAMOND FILMS DOPED WITH B, P, LI AND NA DURING CRYSTAL-GROWTH

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 10(9) Omega cm, undoped films even more than 10(16) Omega cm. 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).