Amorphous Si thin films prepared by vacuum arc deposition

Abstract Amorphous Si (a-Si) thin films up to 0.5 μm thick were prepared by vacuum arc deposition (VAD) on glass and polyimide substrates from a water-cooled, heavily boron doped (2.2 × 10 19 cm −3 ) Si cathode. The cathode spots (CSs) were swept along the cathode surface using the superposition of opposite-directed magnetic fields from two coils: a smaller coil located behind the cathode, and a second, larger coil encompassing the interelectrode region. The CSs rotated on the cathode surface in trajectories of adjustable radii of up to 46 mm. The macroparticles were filtered from the plasma jet using a quarter torus magnetic filter. Two additional Helmholtz coils were used to collimate the plasma exiting from the magnetic filter onto the substrate. The deposition chamber was evacuated with a diffusion pump, and the pressure during deposition was typically less than 8 × 10 −5 Torr. No process gas was introduced. Deposition rates of up to 1.7 nm s −1 were achieved. The films were found to be amorphous using X-ray and transmission electron diffraction. The films' boron doping was measured by secondary ion mass spectroscopy and found to be the same as that of the silicon cathode. The electrical conductivity of the films was measured as a function of temperature and found to vary from 1.5 × 10 −5 S cm −1 at room temperature up to 1.2 × 10 3 S cm −1 at 280 °C, with an activation energy of 0.4 eV. These values are of the same order of magnitude as the conductivity of glow discharge prepared hydrogenated a-Si films (a-Si:H), even though no hydrogen was introduced into the VAD system. The optical transmission spectrum of the films was measured from 280 nm up to 820 nm. The absorption coefficient at 800 nm is 1.1 × 10 4 cm −1 , and at 320 nm it is 8.5 × 10 4 cm −1 .