J. Phys. Radium 11, 375-379 (1950)
DOI: 10.1051/jphysrad:01950001107037500

Propriétés optiques des lames minces de silicium

P. Cotton

Faculté des Sciences, Marseille

Abstract
Investigations on thin films of silicon. - One can determine the complex index and the thickness of a thin metallic film deposited on glass, by means of values of the reflecting coefficients, R against air, R1 against glass, and the transmission factor T of the film. By making use of deposits in simple gradings this determination can be quite accurate. At the same time and on the same base, four or five layers are deposited, whose thicknesses have known ratios. The optical examination of these different layers makes it possible to trace out the curves giving R, R' and T as a function of the optical thickness of the film. Comparison of the experimental and theoretical curves gives the values of ν, k =x/y and the thickness of each layer. I have applied this method to thin films of silicon. The layers are obtained by thermal evaporation; a convenient arrangement (Talbot dise) reduces the thickness of the different layers during deposition. The measurement of the reflexion and trarsmission coefficients have been made by a photocell and by photographic photometry. They have been determined for a given number of visible radiations. The layers of silicon so obtained give beautiful colours, especially when observert by reflexion on the glass side. The maxima in the reflecting coefficients are very marked; the transmission factors exhibit oscillations. The complex index of silicon depends upon the condition of deposition. Slow deposition in a good vacuum on well outgassed supports give layers with an index of refraction in the neighbourhood of 4,2, and a coefficient of extinction k' =x/ν a value of 0.10. When the deposition is rapid or the vacuum insufficient, the layers are less stable and much less absorbing : the index of refraction reaches a higher value, but the coefficient of extinction diminishes considerably (it reaches 0.03). These less absorbing films are unfortunately not of use because of their lack of stability.

PACS
4279W - Optical coatings.
4270 - Optical materials.
7820C - Optical constants (including refractive index, complex dielectric constant, absorption, reflection and transmission coefficients, emissivity).

Key words
optical films -- optical materials -- refractive index -- silicon