Quantitative in-situ Kelvin probe study of boron doping in hydrogenated amorphous silicon and hydrogenated amorphous silicon carbide

Abstract

We used an in-situ Kelvin probe to study the boron doping of hydrogenated amorphous silicon (a-Si: H) and hydrogenated amorphous silicon carbide (a-SiC: H) films. Secondary-ion mass spectrometry measurements show that incorporation ratio [B]/[Si] is close to unity for both materials doped with either diborane or trimethylboron. In the case of diborane, Kelvin probe measurements indicate a higher doping efficiency in a-Si: H material than in a-SiC: H material. The variation in the contact potential of a-Si: H with the diborane concentration has been quantitatively studied and compared with the variation in the activation energy of the dark conductivity. From numerical calculations a 3 × 10¹² cm⁻² eV⁻¹ surface density of states, compatible with the experimental results, was found. The change in the band bending and the shift of the bulk Fermi level of a-Si:H during the doping were then deduced.