Optical properties of As2S3 layers deposited from solutions obtained by chemical reaction

Abstract

This paper deals with three approaches for the preparation of arsenic sulfide layers from solutions. First approach employs arsenic sulfide solutions obtained by dissolving powder of arsenic sulfide glass in n-propylamine. Second approach, a novel one, employs amorphous arsenic sulfide precipitated by chemical reaction of arsenic trichloride and ammonium sulfide. The precipitate was dissolved in n-propylamine. Third original approach relays on the same chemical reaction carried out in a mixture of n-propylamine and water that prevents the precipitation. By using all the approaches input arsenic sulfide solutions with a concentration of 0.33 mol/l were fabricated and applied onto glass slides by dip-coating method with withdrawing velocities of 50, 100, 200, and 250 mm/min. Applied layers dried in vacuum at 60 °C for 1 h and thermally treated at 180 °C for 30 s were characterized by optical and atomic force microscopy as well as by transmission spectroscopy in a wavelength range of 300–2500 nm. Refractive indices, thicknesses and band gaps were estimated from measured spectra. A maximum refractive index of about 2.15 at 600 nm and thicknesses up to 220 nm were determined on layers fabricated from input solutions obtained by dissolving of arsenic sulfide glass. Arsenic sulfide layers prepared on the basis of the arsenic sulfide precipitation exhibit refractive indices up around 1.90 and thicknesses up to 410 nm. Photonic band gap values on a level of 2.2 eV have been determined on these layers. On the other hands, composite layers prepared by reaction of arsenic trichloride and ammonium sulfide in the solution of n-propylamine and water exhibited low transparencies, refractive indices around 1.7 and thicknesses of about 2 µm.