ELECTRICAL-PROPERTIES OF BORON-DOPED DIAMOND FILMS AFTER ANNEALING TREATMENT

Trimethylborate (B(OCH3)(3)) was used to obtain boron-doped (p-type) polycrystalline diamond thin films on a silicon substrate using microwave plasma-assisted chemical vapor deposition. The effect of the doping agent (trimethylborate) was characterized in terms of electrical properties, and the current-voltage (I-V) characteristics of the boron-doped diamond films using aluminum as contacts at room temperature were examined. A surprising result was that annealing improved the electrical properties of boron-doped diamond films. As the boron concentration increased, the forward current decreased because of the effects of impurity scattering, and the I-V characteristics were still rectified. After the samples were annealed in a helium ambient at 900 degrees C for 30 min, the I-V characteristics changed: the higher the concentration of boron in the doped diamond films, the more ohmic was the observed behavior. The differences in the I-V characteristics of annealed and non-annealed films were subsequently confirmed by Fourier transform infrared spectroscopy (FTIR), capacitance-voltage (C-V) measurements, and cathodoluminescence (CL) experiments. The results of these experiments demonstrated that the annealing treatment caused boron atoms initially in inactive sites (e.g. interstitial or clustering sites) to be incorporated into substitutional sites. The increase in substitutional boron atoms altered the I-V characteristics of the boron-doped diamond films.