Low density of defect states in hydrogenated amorphous carbon thin films grown by plasma-enhanced chemical vapor deposition

The density of electronic defect states in most forms of amorphous carbon deposited at room temperature is found so far to be very high (10(18)-10(22) spins cm(-3)). In this letter, we demonstrate that the radio-frequency plasma-enhanced chemical vapor deposited hydrogenated amorphous carbon (a-C:H) thin film exhibits the lowest spin density of the order of 10(16) cm(-3), investigated by using electron spin resonance (ESR) spectroscopy, a very promising reproducible result comparable with high-quality a-Si:H. In addition, the optical gap of a-C:H has been tailored between a wide range, 1.8-3.1 eV. The ESR spectra of all the films reveal a single Lorentzian line whose linewidth DeltaH(pp) varies strongly with the optical gap. Also, there is a strong dependence of spin density on the optical gap, and we show that this dependency is a direct result of structural changes due to sp(3)/sp(2) carbon bonding network. (C) 2001 American Institute of Physics.