Validity of Swanepoel's Method for Calculating the Optical Constants of Thick Films

Abstract

Optical constants, dispersion and oscillator parameters of dierent thicknesses of amorphous Ge25Cd5Se70 lms have been deposited onto glass substrates using thermal evaporation technique. The optical constants have been investigated by optical spectrophotometry measurements. The straight forward analysis proposed by Swanepoel, which is based on the use of the extremes of the interference fringes has been used in order to derive the refractive index and the lm thickness in µm range. The refractive index could be extrapolated by the Cauchy dispersion relationship over the whole spectral range, which extended from 400 to 2500 nm. It is observed that, refractive index n increases with the lm thickness. The possible optical transition is found to be allowed indirect transition with energy gap increase from 1.915 to 1.975 eV with increasing lm thickness. The dispersion of the refractive index is discussed in terms of the WempleDiDomenico single oscillator model. The interband oscillator wavelength, the average oscillator strength, and the optical conductivity were estimated for dierent thicknesses of amorphous Ge25Cd5Se70 lms.

Role of Bismuth and Substrate Temperature on the Optical Properties of Some Flash Evaporated Se<SUB>100-X</SUB> Bi<SUB>X</SUB> Glassy System

“…Other researchers have also found selenium rich binary and ternary glasses to obey the indirect rule transition [16] [17]. Indirect optical band gap energy from the studied thin films was observed to decrease with increase in substrate temperature and bismuth content as shown in Figure 6.…”

Physical properties of electron beam evaporated CdTe and CdTe:Cu thin films

“…The reduction in energy band gap may also be due to the extension of localized states in amorphous structure. 15 As observed from the XRD pattern, the unsaturated bond in the amorphous structure due to the insufficient number of atoms causes defects that are responsible for the formation of localized states. The tailing of localized states in the band gap can be studied using the empirical Urbach rule as given below…”

“…This is because, during the film deposition at room temperature, the low thermal activation energy leads to the formation of some unsaturated bonds along with the saturated bonds due to the insufficient number of atoms and hence the atoms may not be able to sit in its lattice position, which leads to distortion. 15 Therefore, the films are in amorphous nature.…”

Thermally evaporated CdTe thin films for solar cell applications: Optimization of physical properties

“…Lowest dielectric constants were found for the film deposited at a substrate temperature of 250 °C. This can be attributed to high crystallinity of the film [16] as indicated in The optical conductivity (σo) is useful for studying the electronic states in materials and can be calculated using the formula [34,35,36];…”