Deposition of a-Si,Sn:H alloy films by reactive magnetron sputtering from separate Si and Sn targets

Abstract

Listen

Translate article

We have deposited thin film a-Si,Sn:H alloy films in a dual magnetron sputtering system, and have studied the chemical bonding of the constituent atoms by infrared (IR) absorption spectroscopy, Auger electron spectroscopy (AES), and x-ray photoelectron spectroscopy (XPS). We have also measured the band-edge optical absorption, the photoconductivity, and the temperature dependence of the dark conductivity. We find that the variation of the optical band gap, the dark conductivity and the photoconductivity are essentially the same in these films as in films produced by the glow discharge decomposition of silane (SiH4) and either SnCl4 or Sn(CH3)4. For Sn concentration as high as 26 at. %, we cannot detect SnH vibrations by IR. We find that the optical gap decreases monotonically with increasing Sn concentration, but that the dark conductivity does not display a conduction mechanism with an activation energy close to one-half of the optical gap. Instead, both the dark and photoconductivities display a transition to a hopping conduction mechanism at a Sn concentration between about 1 and 2 at. % (this corresponds to an optical gap just below 1.7 eV). We propose a model for this transition in which the Sn is incorporated in nontetrahedral bonding geometries.