Extracting the optical parameters of thermally evaporated Se film by modelling of transmittance spectra: Effect of heat treatment

Abstract

Thin Se films with an appropriate thickness were deposited by the thermal evaporation technique on glass substrates that are grasped at a temperature of ∼ 300 K. The as-deposited amorphous Se thin films were heat-treated in N 2 ambient for 1 h at different annealing temperatures that ranged from 323 to 363 K. The transmittance spectra of green and annealed Se films have been measured at vertical incidence angle along the wavelength range of 300-2500 nm. For the first time, the dielectric function (OJL2) model modified by O'Leary, Johnson, Lim was used alone to fit very well the transmission spectra along the whole wavelength range and extract the optical parameters of Se films. For each value of photon energy, the value of the complex dielectric function of all examined Se films was obtained. By simulating, the model parameters (absorption coefficient α, real and imaginary dielectric constants, refractive index n and optical bandgap Eg) and the film thickness have been deduced. We found that the index of refraction increased by increasing the annealing temperatures. Optical bandgap energy of Se films changes slowly from 2.0 eV of virgin a-Se film to 1.6 eV as the annealing temperature was raised to 343 K and then increased again from 1.93 eV to 2.2 eV for films annealed at temperatures that ranged from 348 to 363 K. By heat treatment crystallization of a-Se films occurred at and above the annealing temperature of 348 K that was confirmed by XRD patterns. The amorphous film showed a smooth surface consisting of very small grains of 40 nm size and low roughness of 1.9 nm. The grain size decreases, while roughness increased by increasing the annealing temperatures.

Controlling the optical properties of hafnium dioxide thin films deposited with electron cyclotron resonance ion beam deposition

“…It can also be observed that the transmittance data of samples shown exhibit interference effects. These interference fringes can be used as an indicator for the thickness of the films [31], where it can be observed that the films have different thickness due to the different configurations and oxygen percentages. As previously mentioned, all coatings have the same deposition time of 72 h, where the thicknesses varies between 140 -270 nm, dependent on the coating configurations.…”

“…OJL model is used to describe the interband transition in the amorphous semiconductors [30,31]. This model assumes the parabolic shape valance and conduction band of the DOS, with tail states exponentially decaying into the bandgap [29][30][31].…”

“…OJL model is used to describe the interband transition in the amorphous semiconductors [30,31]. This model assumes the parabolic shape valance and conduction band of the DOS, with tail states exponentially decaying into the bandgap [29][30][31]. The said tail states are the results of the disorder present in amorphous semiconductor, where this is also known as the Urbach tail [32].…”

“…Where E 0 can be acquired via SCOUT. The other OJL interband transitions within SCOUT are as follows [30,31,33,34]:…”

“…(3) Run the "automatic fit", where the downhill simplex method is applied to vary the fit parameters in order to minimize the deviation between the experimental and simulated values, until an optimal fit is obtained. ( 4) The E 0 , n and thickness values can now be obtained [30,31].…”