Boron-doping effects on local structures of semiconducting ultrananocrystalline diamond/hydrogenated amorphous carbon composite thin films fabricated via coaxial arc plasma: an x-ray absorption spectroscopic study

Abstract

Ultrananocrystalline diamond / hydrogenated amorphous carbon composite thin films synthesized via coaxial arc plasma possess a marked structural feature; diamond grains embedded in an a-C and a a-C:H matrices that are the largest constituents of the films. Since the amorphous nature distinctly yields much larger light absorption coefficients as well as a generation source of photo-induced carriers with UV rays, these films can be potential candidates for deep-ultraviolet photodetector applications by proper engineering. P-type conductions of the films have been realized by doping boron in experimental conditions and their electrical characteristics were investigated recently. This work that utilized near-edge X-ray absorption fine structure spectroscopy reveals that bonding state σ* C-B of diamond surfaces are formed preferentially and can be an origin of an enhancement of electrical conductivities, by correlating the results with the above-mentioned investigation, and structural distortion would be caused at an early stage of the doping. Further doping into the films lessens the amount of unsaturated bonds such as π* C ≡ C and π* C = C , resulting in stabilization of the whole film structures. Our work suggests a fundamental case model of boron-doping effects on the films and a potential for an improvement of device capabilities consisting of the films as photovoltaics.