Studies of phosphorus doped diamond-like carbon films

Phosphorus doped diamond-like carbon (DLC) films have been deposited on Si substrates using CH4-based RF plasmas with addition of 0-21% PH3 into the source gas mixture. Scanning Auger studies reveal that the films contain P:C ratios as high as 0.891 and that the degree of P incorporation is roughly proportional to the PH, concentration in the gas phase. Reduction in intensity and finally loss of the laser Raman G-band with increasing P content in the film shows that excessive P incorporation causes amorphisation of the film. The electronic properties of the films, such as held emission threshold and optical band gap, are a complicated function of film composition. Minimum field emission thresholds occur at P:C ratios of around 0.02, and voltage bias values similar to 30% lower than that for the undoped film. Annealing in vacuum at 150 degrees C can improve the field emission threshold of the low P content films by a factor of four. (C) 2000 Elsevier Science S.A. All rights reserved.