Optical-constant calculation of non-uniform thickness thin films of the Ge10As15Se75 chalcogenide glassy alloy in the sub-band-gap region (0.1–1.8eV)

Abstract

Optical-transmission spectra are very sensitive to inhomogeneities in thin ®lms. In particular, a non-uniform thickness produces a clear shrinking in the transmission spectrum at normal incidence. If this deformation is not taken into account, it may lead to serious errors in the calculated values of the refractive index and ®lm thickness. In this paper, a method ®rst applied by Swanepoel for enabling the transformation of an optical-transmission spectrum of a thin ®lm of wedge-shaped thickness into the spectrum of a uniform ®lm, whose thickness is equal to the average thickness of the non-uniform layer, has been employed. This leads subsequently to the accurate derivation of the refractive index in the subgap region (0.1±1.8 eV), the average thickness, as well as a parameter indicating the degree of ®lmthickness uniformity. This optical procedure is applied to the particular case of freshly-prepared ®lms of the Ge 10 As 15 Se 75 ternary chalcogenide glassy alloy. The dispersion of the refractive index is discussed in terms of the Wemple±DiDomenico single-oscillator model. The optical-absorption edge is described using the`non-direct transition' model proposed by Tauc, and the optical energy gap is calculated by Tauc's extrapolation. Finally, the photo-induced and thermally induced changes in the optical properties of the aGe 10 As 15 Se 75 layers are also studied.

Determination of the optical parameters of a-Si:H thin films deposited by hot wire–chemical vapour deposition technique using transmission spectrum only

“…Furthermore, the optical absorption edge can be seen clearly for all three a-Si:H samples under investigation. Our results are very similar to the results of Marquez et al [23] and have similar trend as those shown by El-Sayed and Amin [24]. Recently, Sharma and Katyal [25] have also observed similar behaviour of extinction coefficient for a-(As 2 Se 3 ) 90 Ge 10 glassy alloy.…”

Effect of isomorphic atom substitution on the refractive index and oscillator parameters of TlInS2xSe2(1‐x) (0.25 ≤ x ≤ 1) layered mixed crystals

“…As a whole, the obtained picture is consistent with the well-known fact that refractive index and the energy gap are inversely related to each other [11]. The oscillator energy E so is an "average" energy gap and it is approximately equals to two times of the lowest direct band gap E gd (E so ≈ 2.0 E gd ) [14][15][16][17]. In this study, the [18,19].…”

Optical constants of TiO1.7 thin films deposited by electron beam gun

“…The spectral distribution of the absorption coefficient α of the films was calculated by two procedures, the first from the relation α = 4πk/λ, depend on the values of k calculated using Swanepoel's method and the second from the formula [9], α = (1/d).ln((1 − R) 2 /T). The obtained values of α from Swanepoel's method and the well-known formula in this region are approximately in the same nearly in magnitude.…”