Modulating Band Gap of Boron Doping in Amorphous Carbon Nano-Film

Amorphous carbon (a-C) films are attracting considerable attention to due their large optical band gap (E(opt)) range of 1–4 eV. But the hopping conducting mechanism of boron doping a-C (a-C:B) is still mysterious. To exploring the intrinsic reasons behind the semiconductor properties of a-C:B, in this work, the boron doping a-C (a-C:B) nano-film was prepared, and the growth rate and E(opt) changing were analyzed by controlling the different experimental conditions of magnetron sputtering. A rapid deposition rate of 10.55 nm/min was obtained. The E(opt) is reduced from 3.19 eV to 2.78 eV by improving the substrate temperature and sputtering power. The proportion of sp(2)/sp(3) increasing was uncovered with narrowing the E(opt). The shrinking E(opt) can be attributed to the fact that boron atoms act as a fluxing agent to promote carbon atoms to form sp(2) hybridization at low energy. Furthermore, boron atoms can impede the formation of σ bonds in carbon atom sp(3) hybridization by forming B–C bonds with high energy, and induce the sp(3) hybridization transfer to sp(2) hybridization. This work is significant to further study of amorphous semiconductor films.