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 sp²/sp³ 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 sp² hybridization at low energy. Furthermore, boron atoms can impede the formation of σ bonds in carbon atom sp³ hybridization by forming B-C bonds with high energy, and induce the sp³ hybridization transfer to sp² hybridization. This work is significant to further study of amorphous semiconductor films.