Groupe de Physique Statistique

Homogeneous amorphous Si1-xSnx alloys have been prepared by coevaporation on cold substrates over a wide composition range, 0x0.50. Their complex dielectric constant has been accurately determined between 0.5 and 3 eV by combining different methods on films with different thicknesses (from 30 to 300500 nm). The derivation of two characteristic alloy parameters (the optical gap and the average gap) from these data is discussed in detail. While the optical gap decreases linearly with increasing x, the average-gap variation shows a change in slope for x0.30, suggesting a modification of the alloy average bonding. A careful analysis of the overall evolution upon alloying of the 1 and 2 spectra supports the conclusion that these a-Si1-xSnx alloys are chemically ordered.