Electrical Effect of Vacuum-Evaporated Alpha-NPD on Oxygen-Terminated Boron-Doped Chemical-Vapor-Deposited Homoepitaxial Diamond Films

Electrical properties of chemical-vapor-deposited (CVD) homoepitaxial diamond layers, based upon Hall effect measurements in the temperature range from 100 K to 300 K, have been investigated when an organic material, N,N-diphenyl-N,N- bis(1-naphthyl)- 1,1biphenyl- 4,4diamine ( -NPD), was thermally deposited on them. In cases of O-terminated B-doped (p-type) diamond films with different carrier densities, substantial reductions in the electric conductivity due to hole density reductions were observed in the temperature range from 170 K to 200 K, where the Hall coefficients significantly changed. At temperatures higher than 200 K, however, it is found that the sheet conductivity of the substrate diamond layer was increased after the -NPD deposition to values larger than those measured before the -NPD deposition. These results indicate that a substantial amount of holes can be transferred from the CVD diamond film to the overlayered -NPD film when an appropriate interface was formed between the -NPD and diamond films. The possibility will be discussed that CVD diamond films can be applicable as a transparent anode material and a hole transport material with a extremely high thermal conductivity and a strong chemical inertness for organic light-emitting diodes.