Investigation of structural, optical, dielectrical and optical conductivity properties of BaTiO3, Al0.01Ba0.99TiO3 and La0.01Ba0.99TiO3 thin films prepared by Pulsed Laser Deposition technique (PLD)AbstractPulsed Laser Deposition technique (PLD) was used to prepare BaTiO3 (BTO), Al0.01Ba0.99TiO3 (ABTO) and La0.01Ba0.99TiO3 (LBTO) thin films. The structure of these films were carried out using X-Ray Diffraction (XRD), while the surface topography were carried out using Scanning Electron Microscopy (SEM). This study had shown that, these films had nano polycrystalline structure.
The optical properties of these samples were studied. The optical parameters such as optical energy gap, refractive index, extinction coefficient, dielectric loss and dielectric tangent loss for these films were determined. The determined values of oscillating energy (Eo), dispersion energy (Ed) had increased respectively for the (BTO), (ABTO) and (LBTO) thin films. While the values of both (effective mass/carrier concentration) (N/m*) and infinity permittivity (µ€ћ) had decreased for respectively for the (BTO), (ABTO) and (LBTO) films.
On the other hand both two terms of optical conductivity (real part (1) and imaginary part (2)) and the ratio of Surface Energy Loss Function SELF /Volume Energy Loss Function (VELF) were determined optically for these films.Keywords :- BaTiO3, Al0.01Ba0.99TiO3 and La0.01Ba0.99TiO3 thin films, Pulsed Laser Deposition (PLD), structure, optical properties and dielectric results.1. IntroductionIn recent years, ternary compounds and ferroelectric materials especially which were prepared in a form of thin films have attracted attention. These materials exhibited potential in many important applications including; dynamic random access memories (DRAMS) . In addition, strip-loaded type optical waveguide structures based on BaTiO3 thin film . Moreover, it is promises to achieve high levels of component integration in micro-photonic applications such as light source, modulators . As it is well known, that doping of the rare is an effective and good method to improve all the physical properties . Many authors [5-9] had studied influence of doping physical properties of the Ba oxide films. On the other hand ferroelectric properties of BiO3 compounds had studied [10-11]. R. Maier et al  had studied the physical properties of BaFexTi1€’xO3. The doping effect on the Photoluminescence (PL) of BaTiO3-CaTiO3 ceramics was studied . The elctrooptical modulation of BaTiO3 crystal thin film had been studied [14,15]. The physical properties dependence on temperature for both BaTiO3 and SrTiO3 were studied, and it was found that the optical results has been affected by temperature .M. R¶ssle et al  studied the influence of temperature on band gap of both SrTiO3 and BaTiO3 using optical spectroscopy. On the other hand, S.Saha et al  had studied physical properties of BaTiO3, they found that the studied samples had a direct band gap of 1.2 eV. The optical properties of both perovskites bulk BaTiO3 and SrTiO3 had been studied . The electro-optical properties of BaTiO3/ZnO heterostructures had been studied . It was found that the linear electro-optical affect on the energy gap of these samples. The physical properties doped BaTiO3 (BT-Tm) were studied . Optical and electrical properties of BaTiO3 nanocrystals based on the reactions of BaCO3 were studied . It was found that, the BaTiO3 nanocrystals had a direct band gap of about 3.42 eV. On the other hand, optical and nonlinear optical properties of BaTiO3 samples had been studied [23-27]. The thickness affected the electrooptical properties of BaTiO3 thin films . The influence of temperature on physical properties of BaTiO3€’ґ were studied . The influence of doping on the optical physical properties of BaTiO3 samples were studied by many authors [30-37]. The structure, Hall effect of La0.01Ba0.99TiO3 had studied .In this paper, we have successfully fabricated thin films of BaTiO3, La0.01Ba0.99TiO3 and Al0.01Ba0.99TiO3 on quartz substrates by pulsed laser deposition. The structure and optical properties of the films were measured. Moreover, optical parameters and dielectric constants were estimated.3. Results and Discussion3.1. StructureX-Ray Diffraction (XRD) patterns of a BaTiO3, La0.01Ba0.99TiO3 and Al0.01Ba0.99TiO3 thin films are shown in Fig. 1. From this figure it was noticed that the all these films had polycrystalline structure, while the doping with Al and La affect on the crystallinty of these films, this clearly appear at planes (108), (407) and (211). The surface topography of these films were studied using SEM as shown in Fig.2. From this Fig it is clear that, the grain size of these samples increase by the addition of both Al and La, which affect on optical and dielectrical properties.The crystallite size (Cs) of these films has been calculated using Sherrer’s formula  (1)where both ” is the wavelength of the used X-ray, is the Bragg’s angle and І (the FWHM of the peak) is expressed in radians. While the dislocation density was determined by : (2)The lattice strain (Ls) , which affects on the broaden of the X-ray peaks and also on the optical and dielectric results, was determined using  (3)Another important factor is that, the number of crystallites per unit area (N), which has been determined using the following equation  (4)where d is the film thickness. The calculate values for these studied samples are shown in table 1.On the other hand the surface topography of these studied samples are shown in Fig 2(a, b and c), from this Fig it is clear that Al0.01Ba0.99TiO3 sample had the greatest grain size compared with the other two samples which is agree with X-Ray results.3.2. Optical resultsFigs 3 a,b show the optical transmission (T) and reflection (R) for the studied. From Fig. 3a, it could be noticed that the BaTiO3 and Al0.01Ba0.99TiO3 film had nearly the same values of (T), while La0.01Ba0.99TiO3 films had a different behavior, this could be attributed to, the optical properties of La is completely differ from the optical properties of Al. The same behavior of these samples is the same for reflectance spectra as shown in Fig. 3b. The absorption coefficient (±) of these investigated films were calculated from both the transmittance and reflection spectra as from the following equation : (5) where d is the film thickness. The optical energy gap (Eg) is determined from the absorption spectra curves at fundamental absorption region near the absorption edge using the empirical equation : (6)where A is a constant, Ѕ is the frequency of the incident radiation and h is Planck’s constant. Firstly the behavior of the absorption coefficient with photon energy (hЅ) was estimated as shown in Fig. 4a, while Fig. 4b, shows the relation between (±.hЅ)2 and (hЅ) in order to determine the direct transition for these studied films. The optical direct energy gap Egdirc was estimated from the extrapolation of the linear part of the curves in Fig. 5. for all samples, From this Fig. it was noticed that found that the BaTiO3 film had a Egdirc of value (3.80 eV), Al0.01Ba0.99TiO3 film had a Egdirc of value (3.65 eV), while La0.01Ba0.99TiO3 film had a Egdirc of value (3.50 eV). This means that the kind of dopant play important rule for change optical energy gap for the investigated film, this is due to the change in crystallinty of these films, which allow to increase the electrons mobility which decrease the energy gap.The value of the Urbach energy Eo was calculated according to Urbach equation  (7) The Eo value is calculated from the slope of the linear part of the logarithmic dependence of (±) on (hЅ) as shown in Fig.4c. The values of activation energy for these studied samples is shown in table. 2. The extinction coefficient (k) for these films were calculated from the relation :- (8)Where ( “) is the wave length of the incident light. The relation between extinction coefficient (k) of these films with (hЅ) was studied as shown in Fig. 4d, from this Fig. it was seen that the BaTiO3 film had the highest value of (k) compared with the another thin films, this is due to the small values of the electron mobility of the BaTiO3 thin films w.r.t. the other films. The refractive index (n) of this films with were calculated using the following equation  (9) (10)Where T+ is the highest value of the transmittance extreme, T- is the lowest value of the transmittance extreme and ns is the refractive index of the used substrate. Fig. 5a shows the dependence of (n) on the (“) for BaTiO3, Al0.01Ba0.99TiO3 and La0.01Ba0.99TiO3 thin films. From this Fig. all these films had the same behavior of the refractive index , while the La0.01Ba0.99TiO3 film had a lower value of the (n) compared with the other films. The values of (n) of these thin films was analyzed using the concept of the single oscillator and can be expressed by the Wemple”DiDomenico relationship  (11)where E is the photon energy, The values of Eo and Ed are obtained from the intercept and the slope resulting from the extrapolation of the line of Fig 5b. The values of Eo and Ed for all samples are shown in Table 2. From this table it was seen that the value of Eo~ 2Eg. The single – oscillator model parameters Eo and Ed are related to the imaginary part of the complex dielectric constant (µ2), the M-1 and M-3 (first and third order of moments) for optical spectrum  can be derived from the relations: (12) (13)Table 2. shows the values of the M-1 and M-3 for these studied thin films. The oscillator strength (f) which was calculated as follow : (14)The value of the oscillator strength is shown in Table 1, from this Table it was seen that type of dopant affect strongly the field strength values, due to the increasing of free electrons with doping.The (n)2 on (“)2 for the studied thin films is shown in Fig. 5c. this phenomena was studied in order to determine (N/m*) using the following equation : (15)Where µL is the lattice dielectric constant, µo is the permittivity of free space, e is the charge of electron, From this figure the slope equal to the value of (e.N/4c2µom*), so the effective mass of these films were calculated as shown in Table. 2. The kind of dopant affect strongly on the values of the calculated effective mass for these films.3.3. dielectrical and optical conductivity resultsThe dielectric loss (µ) and dielectric tangent loss (µ\) for these films were calculated using the equations  : (16) (17) Figs 6 a,b show both of (µ) and (µ\) on (hЅ) for all the studied films. From Fig. 6a it was seen that for BaTiO3, Al0.01Ba0.99TiO3 films they had the same values and behavior of the (µ), this could be attributed to, that these samples had the same behavior of both refractive index and also the extinction coefficient. Figs c,d show the real part of optical conductivity (1) and imaginary part of optical conductivity (2) dependence on photon energy for these films. The optical conductivity was calculated from the following equations  (18) (19)The important electron transitions in both cases of materials such as thin film and bulk material was described using two important parameters which were (SELF) and VELF). The relation between (VELF/SELF) and (hЅ) for these samples is shown in Fig. 7a. Both of (VELF, SELF) were calculated from the imperial equations :- (20) (21)Another important factor is electric susceptibility(c) which is he degree of polarization of a dielectric material in response to an applied electric field. The greater the electric susceptibility, the greater the ability of a material to polarize in response, (c) was determined using the following equation  (22)The electric susceptibility (c) dependence on photon energy for these studied samples is shown in Fig. 7b, from this Fig it was (c) increases with photon energy for all these samples, this means that these samples had an ability to polarize and also affected strongly with the Appling electric field. 4. ConclusionThe effect of both La and Al doping on the BaTiO3 thin films properties had been studied. The structure results had shown that, doping with both of Al and La had effected on the surface topography of these films, it was found that La doping led to an increase in the particle grain size. Doping with both of Al and La had effected on both of optical and dilelctrical results. The direct energy gap increase depending on the type of dopant, also both of desperation energy and oscillating energy had increased depending on the dopant type. The effective mass ratio with the carrier concentration and Infinity permittivity had decreased by changing the dopant type. The behavior of both (µ) and (µ\ ) had also changed depending on the type of dopant.The type of dopant plays an important rule in changing and controlling the physical properties of the samples, this means that we can got an excellent properties of these samples only by changing the type of dopant by small ratio. Figures Figure 1. The XRD pattern of (a) BaTiO3, (b)La0.01Ba0.99TiO3 and (c)Al0.01Ba0.99TiO3 Figure 2. The FE-SEM image of (a) BaTiO3, (b) La0.01Ba0.99TiO3 and (c) Al0.01Ba0.99TiO3 thin films grown on quartz substrates by pulsed laser deposition.Figure 3. (a) The transmission and (b) refletance spectra for a) BaTiO3, La0.01Ba0.99TiO3 and Al0.01Ba0.99TiO3 thin films grown on quartz substrates by pulsed laser deposition.Figure 4. The dependence of (a) absorption coefficient(±), (b) (±.hЅ)2, (c) Ln (± ) and (d) extinction coefficient on photon energy for BaTiO3, La0.01Ba0.99TiO3 and Al0.01Ba0.99TiO3 thin films grown on quartz substrates by pulsed laser deposition.Figure 5. The dependence of (a) refractive index (n) and wave length (b) (n2-1)-1 and wave length and (c) (n2) and (wave length)2 for BaTiO3, La0.01Ba0.99TiO3 and Al0.01Ba0.99TiO3 thin films grown on quartz substrates by pulsed laser deposition.Figure 6. The dependence of (a) dielectric loss (µ) (b) (dielectric tangent loss (µ\), (c) real part of optical conductivity (1) and (d) imaginary part of optical conductivity (2) on photon energy for BaTiO3, La0.01Ba0.99TiO3 and Al0.01Ba0.99TiO3 thin films grown on quartz substrates by pulsed laser deposition.Figure 7. The dependence of (a) VEL/SEL and (b) electric susceptibility c on photon energy for BaTiO3, La0.01Ba0.99TiO3 and Al0.01Ba0.99TiO3 thin films grown on quartz substrates by pulsed laser deposition. Table (1) The structural results analysis spectral half width (І ) grain size (Cs), dislocation density () line/cm2, The number of crystallites per unit area (N) / cm2 and Lattice strain Ls ) for BaTiO3, La0.01Ba0.99TiO3 and Al0.01Ba0.99TiO3 thin films.Al0.01Ba0.99TiO3 La0.01Ba0.99TiO3 BaTiO3 Lattice strain Ls The number of crystallit-es per unit area (N) / cm2 Disloc-ation density () line/cm2 Grain size Cs (nm) І (FWHM) Lattice strain Ls The number of crystallit-es per unit area (N) / cm2 Disloc-ation density () line/cm2 Grain size Cs (nm) І (FWHM) Lattice strain Ls The number of crystallit-es per unit area (N) / cm2 Disloc-ation density () line/cm2 Grain size Cs (nm) І (FWHM) (hkl)40.00 4.1E+17 1.2E+14 9.05 0.16 27.50 1.3E+17 5.8E+13 13.16 0.11 45.00 5.8E+17 1.5E+14 8.04 0.18 10224.46 9.3E+16 4.6E+13 14.80 0.10 22.01 6.7E+16 3.7E+13 16.44 0.09 29.35 1.6E+17 6.6E+13 12.33 0.12 11099.97 6.3E+18 7.6E+14 3.62 0.40 92.47 5.0E+18 6.5E+14 3.91 0.37 109.97 8.4E+18 9.2E+14 3.29 0.44 10422.64 7.3E+16 3.9E+13 15.98 0.20 22.64 7.3E+16 3.9E+13 15.98 0.20 28.30 1.4E+17 6.1E+13 12.79 0.25 20233.46 2.4E+17 8.5E+13 10.82 0.20 30.11 1.7E+17 6.9E+13 12.02 0.18 36.80 3.2E+17 1.0E+14 9.83 0.22 00613.77 1.7E+16 1.4E+13 26.28 0.22 11.89 1.1E+16 1.1E+13 30.43 0.19 15.02 2.1E+16 1.7E+13 24.09 0.24 20435.17 2.8E+17 9.4E+13 10.29 0.15 30.48 1.8E+17 7.1E+13 11.87 0.13 42.20 4.8E+17 1.4E+14 8.58 0.18 00842.59 4.9E+17 1.4E+14 8.50 0.18 35.49 2.8E+17 9.6E+13 10.20 0.15 47.32 6.7E+17 1.7E+14 7.65 0.20 10857.77 1.2E+18 2.5E+14 6.26 0.24 52.96 9.4E+17 2.1E+14 6.83 0.22 67.40 1.9E+18 3.5E+14 5.37 0.28 22020.73 5.6E+16 3.3E+13 17.46 0.21 18.75 4.2E+16 2.7E+13 19.30 0.19 23.69 8.4E+16 4.3E+13 15.28 0.24 20631.86 2.0E+17 7.8E+13 11.36 0.28 28.45 1.5E+17 6.2E+13 12.72 0.25 34.14 2.5E+17 8.9E+13 10.60 0.30 31448.39 7.2E+17 1.8E+14 7.48 0.21 39.17 3.8E+17 1.2E+14 9.24 0.17 55.31 1.1E+18 2.3E+14 6.54 0.24 22625.48 1.0E+17 5.0E+13 14.20 0.16 20.70 5.6E+16 3.3E+13 17.48 0.13 28.67 1.5E+17 6.3E+13 12.62 0.18 2225.60 1.1E+15 2.4E+12 64.62 0.12 4.67 6.4E+14 1.7E+12 77.54 0.10 6.53 1.8E+15 3.3E+12 55.39 0.14 40715.15 2.2E+16 1.8E+13 23.88 0.14 16.24 2.7E+16 2.0E+13 22.29 0.15 19.48 4.7E+16 2.9E+13 18.57 0.18 211 Table 2:- The calculated physical results of BaTiO3, Al0.01Ba0.99TiO3 andLa0.01Ba0.99TiO3 thin filmsf(eV)2 M-3 M-1 Activation energyeV Static refractive index no EdeV E0eV N/m* µL Energy gap (eV) sample 24.30 2.70 9.00 0.25 1.60 11.30 7.20 1.0E+47 12.0 3.80 BaTiO326.00 2.75 9.44 020 1.62 11.85 7.52 2.0E+47 48.0 3.65 Al0.01Ba0.99TiO327.60 2.80 9.85 018 1.60 12.45 7.80 1.4E+47 40.0 3.50 La0.01Ba0.99TiO3