Phosphorus doping of diamond-like carbon films by radio frequency CVD-cum-evaporation technique

Abstract

Diamond-like carbon (DLC) films have been deposited by cracking methane gas in radio frequency plasma. Phosphorus was incorporated in DLC films by simultaneously evaporating phosphorus during the synthesis of DLC with methane gas by using capacitatively coupled plasma chemical vapour deposition (CVD) technique. The films were characterized by FESEM, XRD, XPS and Raman studies. The band gap of the pristine DLC films was found to be ~2.61eV and it decreased from 2.61eV to 2.31eV with increased incorporation of P in the DLC films. Raman studies indicated the presence of two broad peaks located at ~1360–1396cm−1 (D-line) and ~1542–1548cm−1 (G-line). The peak positions of the D-lines shifted in towards lower wave number with increased incorporation of phosphorus in them. This indicated that the DLC films became sp2 rich with increased incorporation of phosphorus. Electrical resistivity measurements have been carried out. The films were n-type as indicated by hot-probe technique. The values of electrical resistivity of the undoped and doped DLC films were 2.0×102Ω-cm and 0.7×102Ω-cm, respectively. Value of carrier concentrations (Nd) obtained were 2.5×1015cm−3 and 2.2×1016cm−3 for undoped and phosphorus doped DLC film with 3.4 at.% P in DLC, respectively.