Optical gap of fluorinated amorphous carbon films prepared by electron cyclotron resonance trifluromethane and benzene plasmas

摘要

The optical gap of fluorinated amorphous carbon (a-C:F) films, which were prepared by electron cyclotron resonance plasma chemical vapor deposition using trifluromethane (CHF_3) and benzene (C_6H_6) as the source gases, is investigated. The optical gap E_g of the a-C:F films, which were deposited at input microwave power of 140-700 W, pressure of 0.1 - 1.0 Pa and CHF_3/C_6H_6 flow ratio of 1:1-10:1, is in the range of 1.76-3.98 eV and is dependent on the amount of fluorine and C=C bonding in the films. The optical gap E_g increases with raising the amount of fluorine but decreases as the amount of C=C bonding increased. This is because of the decrease in the amount of pi bonding formed by C=C and the increase in that of sigma bonding formed by C-F As a result, the density of state near band edgy reduces and the optical gap becomes wide.