Optical properties of Cd 3As 2 polycrystalline thin films

Abstract

The transmittance T and reflectance R have been measured at normal incidence of light for a set of vacuum deposited Cd 3As 2 thin films of different thickness in the wavelength range of 0.5–10 μm. The measured values T and R in conjunction with the film thickness were used to determine the optical constants (the refractive index n, the absorption index k and the absorption coefficient α) of the films. The lattice dielectric constant was found to be 17.6. Graphical representation of log (αhν) versus log ( 1 λ ) yielded three distinct linear regions. The first region had the photon energy range up to 0.3 eV. The second region had the photon energy range of 0.3–0.9 eV. The third region had the photon energy range of 0.95–2.1 eV. It was found that the only allowed type of optical transitions in the first region was indirect with an energy gap E d ing = 0.05 eV. In the second region, the only allowed type of optical transition was direct with energy gap E g d = 0.72 eV. In the third region, the only allowed type of optical transition was direct with energy gap E g d = 1.56 eV. The last two values were confirmed throughout the graphical representation of- lm( 1 ε ) = f(hv) . The existing allowed optical transitions in the above mentioned three regions were interpreted according to the LinChung model.