Electrical Characterization of Metal Contacts on Diamond Thin Films

ABSTRACTPolycrystalline boron-doped diamond thin films were prepared by microwave-enhanced plasma-assisted chemical vapor deposition. Ti, V, Ta, Nb, Al, Mo and W contacts were prepared by physical vapor deposition and their behavior was studied as a function of the annealing temperature, atmosphere and duration. For Ti contacts, short heat treatments (less than 60 minutes) at 500 °C under argon atmosphere were found to make ohmic contacts for applied voltages up to 50 V. Longer annealing times, more reactive atmospheres, and higher temperatures degraded the contact characteristics. In order to obtain a more complete picture of the interface structure, the capacitance-voltage characteristics and the impedance spectra of the systems were measured between 10 K and 1000 K. The interface contribution to the overall dielectric behavior of the system shows much shallower depletion widths in Ti-diamond (ohmic) contacts than with the non-linear Nb and Ta contacts. The higher values of the contact resistance and the shallower depletion width with Ti can be explained in terms of formation of a thin carbide-like region at the metalsemiconductor interface. The space-charge region width as well as the distribution of localized states in the band gap were also determined. The effect of the microstructure on the electrical properties of the systems is discussed in comparison with the behavior of metal-contacts on single-crystal diamonds.