Étude des corrélations entre paramètres de préparation, caractéristiques électriques et physico-chimiques d'échantillons de a-Si : H dopés ou non

Abstract

Using linear and second-degree regression, we have studied correlations between measurements of electrical conductivity, activation energy, concentration of the various elements (hydrogen, carbon, oxygen, argon, and eventually a dopant: indium, thalium, or antimony), thickness, and some preparation parameters: deposition temperature, mass flow ratio between the various gases intervening in the plasma, and deposition time. We have shown that the deposition rate is the only parameter, in the range studied, that plays an important role for the composition of the intrinsic films. The other parameters, viz. flow ratios of the various gases present in the mixture, temperature, have a limited influence on the composition and the electrical characteristics. The chemical composition measurements have been directly correlated with the electrical measurements. The introduction of a doping metal in the material modifies not only its opto-electrical characteristics, but generally its hydrogen content. Our process of doping by evaporation follows the "universal" behaviour of metals from columns II and V, already known in hydrogenated amorphous silicium. For the p and n films, we have observed that the hydrogen concentration and the width of the energy gap increase first with the dopant concentration and decrease afterwards. The presence of a dopant in the amorphous material leads to a disorder restructuring that changes the chemical composition more than the density of states in the energy gap.