CORRELATION OF TETRAHEDRAL AND TRIHEDRAL BONDING PROPERTIES IN AMORPHOUS CAMPHORIC CARBON THIN FILMS

Abstract

The tetrahedral carbon ( ta-C ) and boron doped amorphous carbon ( a-C:B ) thin films have been grown by pulsed laser deposition. The respective effects of diamond percentages by weight in the target (Dwt%) and boron percentages by weight in the camphoric carbon target (Bwt%), on the tetrahedral (sp3) and trihedral (sp2) bonding properties are discussed. The optical gap Eg and electrical resistivity ρ increase with Dwt%, up to 1.6 eV and 5.63 × 107 Ω cm respectively, for the film deposited using target with 50 Dwt%. We found that the Dwt% has modified the sp3 bonds content and the morphology of the carbon films. On the other hand, the Eg of a-C:B films is almost unchanged at about 0.95 eV up to 10 Bwt% and decreases thereafter to 0.6 eV at 16 Bwt%. The ρ increases initially to 2.29 × 106 Ω cm at 2 Bwt%, and decreases thereafter up to 4.58 × 105 and 1.82 × 104 Ω cm at 10 and 16 Bwt%, respectively. The variation of structural properties, Eg and ρ, can be related to the successful doping of B in the a-C films at low content of Bwt% (up to 10 Bwt%), as the structural properties and Eg remain almost unchanged and the ρ decreased. Since both Eg and ρ decreased sharply with higher Bwt%, this phenomenon can be related to graphitization. In this paper, the dependence of sp3 and sp2 impurity content on the growth and growth conditions of the films are also studied.