Optical properties of amorphous Ba0.7Sr0.3TiO3 thin films obtained by metal organic decomposition technique

Characterization of optical properties of amorphous BaTiO3 nanothin films

“…The obtained value was about 3.92 eV, which was higher than that of polycrystalline BaTiO 3 thin films reported by others [19,24]. It seems to us that the differences in the optical spectra, refractive index and calculated E g might be related to quantum-size effect in BaTiO 3 nanothin film [29]. The quantumsize effect resulted in an increase in the band gap energy if the crystallite dimensions became very small.…”

“…It also indicated the high absorption in the ultra violet region. The transmission of the films was decreased sharply when the wavelength was reduced to around 376 nm, which could be due to the fundamental absorption of light and occurrence of inter-band transitions as it has been mentioned earlier [19,29]. Absorption of the light photon may occur by the promotion or excitation of an electron from the nearly filled valence band, across the band gap into an empty state within the conduction band.…”

“…Transmission spectrum of this film drops rapidly at 376 nm, and the cutoff wavelength occurs at 283 nm, which is due to the fundamental absorption of light. In high absorption region, absorption coefficient, a(k), is related to the energy of incident photons, (hm), by band-to-band transition relation [24,29,31]: where B is a constant and nearly equal to one at absorption edge [24], p is an index that characterizes the optical absorption process and is theoretically equal to 1/2, 2, 3/2 or 3 for direct allowed, indirect allowed, direct forbidden and indirect forbidden transitions, respectively [34]. Absorption coefficient, a(k), is mainly influenced by two factors: (i) scattering losses and (ii) fundamental absorption.…”

“…The usual method of determining band gap energy is to plot a graph between (ahv) n (n = 2 or 1/2 for direct allowed transition and indirect transition, respectively) and photon energy hv, and to compare which value of n gives the best linear relation in the band edge region [29,33]. Whereas BaTiO 3 has direct band transition [4,19,24] and therefore plotting (ahv) 2 versus hv to (ahv) 2 = 0 determinates band gap value for BaTiO 3 nanothin film.…”

Set-Up Method on Properties of Ba_XSr_1-XTiO₃ Thin Films Deposited by RF-Magnetron Co-Sputtering by Projecting Temperature and Stoichiometric Effect

“…The authors explain these differences due to: a) the change in crystal structure [11], b) phase change [15], c) the increase in interatomic space due to excess volume and absence of long-range order in the lattice, in addition to the Burstein-Moss effect due to oxygen vacancies [14] d) the change in size of the microstructure [16], e) the presence of amorphous material and the effect of quantum size [25,26,28].…”