Hydrogenated diamond-like carbon (DLC) was deposited using a radio-frequency plasma-enhanced chemical vapor deposition method. Electrical properties of Al, Au, Ti, and Zr contacts to nitrogen and boron doped DLC films have been studied, and mechanisms of the observed current-voltage (I-V) characteristics are investigated. Linear I-V characteristics were observed for Au, Ti, and Zr contacts to both nitrogen and boron doped DLC films. A band structure model for metal-DLC contact is proposed to explain the observed ohmic contacts. Fermi level shifting at the surface of DLC films produces an ohmic resistive layer instead of a Schottky barrier for metal-DLC contacts. Al contacts to both nitrogen and boron doped DLC films show nonlinear I-V characteristics, which are attributed to a dielectric layer of carbide (Al(4)C(3)) instead of a Schottky barrier suggested by other groups. Inert elements such as Au and Pt, and transition metals such as Ti, Zr and W. which form conductive carbides, are considered good contacting metals for electrical studies of DLC films. (C) 2009 Elsevier B.V. All rights reserved.