Abstract

This study focuses on the study characteristic of the optical absorption of thin films of evaporated hydrogenated amorphous silicon (a-Si: H) prepared in a built Ultra-High Vacuum (UHV). Atomic hydrogen is produced using a plasma discharge tube directed towards the substrate holder. The optical absorption coefficient was obtained in the range of 0.5 to 2.5 eV using optical transmission measurements and Photothermal Deflection Spectroscopy (PDS). The results obtained are comparable to those of films prepared by decomposition of silane. The refractive index of the films decreases when the concentration of hydrogen increases. E_Gbandwidth increases (1.45 to 1.60 eV), the parameter threshold Urbach E₀decreases (from 149 to 62 meV) and finally the number of spins (4 x 10¹⁹ to 6.5 x 10¹⁶ cm^-3) depending on the concentration of hydrogen increases.

Key words: Hydrogenated amorphous silicon, optical absorption, density of electronic states, urbach absorption.