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Investigation of non-linear optical, semiconducting and dielectrical properties of In1-xMnxSe thin films

**Abstract **

In1-xMnxSe (x=0, 0.05, 0.1and 0.15) thin films were evaporated by using thermal evaporation technique. Both of dispersion energy (Ed) and oscillating energy (Eo) were determined. The values of lattice dielectric constant (µL) and free carrier concentration/effective mass) (N/m*) were calculated.

On the other hand, other important parameters such as, the values of first order of moment (M-1), the third order of moment (M-3) and static refractive index (no), were determined.

The both of dielectric loss (µ) and dielectric tangent loss (µ) for these films increased with photon energy and had a highest value near the energy gap Eg. Also, the same behavior was noticed for the real part of optical conductivity and imaginary part of optical conductivity, the relation between Volume Energy Loss Function (VELF) and Surface Energy Loss Function (SELF) were determined.

The Linear optical susceptibility increases with photon energy for all compositions. The nonlinear optical parameters such as, nonlinear refractive index (n2), the third-order nonlinear optical susceptibility, non-linear absorption coefficient (Іc) , were determined theoritically.

Both of The electrical susceptibility (e) and relative permittivity (µr) increase with photon energy and had a highest value near the energy gap. The semiconducting results such as, density of the valence band, conduction band and Fermi level position (Ef) were calculated.

An AIIIBVI semiconductors such as, Ga1-xMnxS [1-3], Zn1€’xMnxSe [4], and finally In1-xMnxSe [5-7] had been studied widely, because of their applications such as, solar energy conversion [8″12], infrared devices [9], lasers [9], photovoltaic applications [13] diodes [14].

The structural and physical properties of InSe were investigated [15″18], InSe thin films had polycrystalline structure after heat treatment [19-22].

The optical properties of InSe thin films were studied [ 23-29], it was found that, InSe samples had an direct energy gap of 1.35 ± 0.02 eV [24], 1.10 eV[25], (2.5 to 3.34 eV)[26] and the values of (1.7, 1.2 and 1.1 eV)[17].

The electrical and dielectrical studies for InSe thin films and crystals were studied [30-35], the ac conductivity is decreased with frequency for InSe [30]. The temperature affect on ac conductivity [31-33], as a result of its strong electron interaction with holes [36]. On the other hand, MnSe had been studied widely, it was noticed that, MnSe crystals had hexagonal structure with lattice constant of (a=5.462 є) and (a=3.63 є; c=5.91 є) [37-39].

The optical properties of MnSe thin films had been studied [40-42], MnSe had energy gap (1.13 ” 1.25 eV) [40-41]. The electrical and dielectrical properties had been investigated [42-44], the electrical resistivity of MnSe decreased with temperature [44].The transport properties of In1-xMnxSe had been studied [7, 45-48], the energy gap and structure dependence on composition of In1-xMnxSe thin films and bulk materials had studied [49-50], these thin films had an amorphous structure [49], the energy gap increases with the x value for both thin films bulk material [50].

The aim of the present work is studying the effect of the composition on dielectrical loss (µ) and dielectric tangent loss (µ), both of real and imaginary part of optical conductivity(1, and 2) respectively, electrical susceptibility ((e)), linear optical susceptibility ((1)), the non-linear optical results such as, nonlinear refractive index (n2), nonlinear absorption coefficient (Іc), non-optical susceptibility ((3)), dielectrical results and finally electronic properties such as Fermi level position (Ef) and density of both of valence conduction band (Nv) and conduction band (Nc) of In1-xMnxSe thin films.

3. Results and discussions

3.1. Dielectric, optical conductivity and linear optical susceptibility results The structure of these thin films with different compositions had an amorphous structure as previous work [49], The optical transmittance (T) and reflectance (R) were measured and discussed in previous work [49]. The single oscillator theory was expressed by the Wemple”DiDomenico relationship [51]: (1)Where n is the refractive index values of these samples which is determined in previous work [49], E is the photon energy, Eo is the oscillator energy and Ed is the dispersion energy. The values of Eo and Ed for all samples are shown in table 1. Fig. 1 shows, the relation of (n2) and (“2) to determine the effective mass ratio with the carrier concentration using the following equation [52]: (2)Where µL is the lattice dielectric constant, µo is the permittivity of free space, e is the charge of electron, n, k is the liner refractive index and the absorption index of these films respectively, which was determined in previous work [49], N is the free carrier concentration for In1-xMnxSe films, and c is the speed of light, so the values of (N/m*) is shown in table 1. From this table it was noticed that, the value of (x) affected on the ratio of (N/m*), the access of Mn, the access of electrons.

The values of the first order of moment (M-1) and the third order of moment (M-3) derived from the relations [52]: (3) (4)Table 1 shows, the values of the M-1 and M-3 for these thin films. The oscillator strength f which was calculated as follow [53]: (5)The values of the f are shown in table 1. Another important parameter depending on both of Eo and Ed is that, static refractive index no which was determined using following equation [54]: (6)The values of no for all these samples are shown in table 1.Fig.2 represents the relation between (n2-1)-1 vs. (hЅ) for these thin films. It is shown that (n2-1)-1 increases as the Mn content increases. The dielectric loss (µ) and dielectric tangent loss (µ) for these films were calculated as follow [55]: (7) (8) Figs. 3(a,b) show both of (µ) and (µ) versus (hЅ) for In1-xMnxSe films. From this Fig., it was seen that, both of (µ) and (µ) decreased with (hЅ) for all studied samples, and the peak maximum values position decreased with increasing Mn content, this is due to the increasing of electron motilities with x values.

The optical conductivity was calculated from the following equations [56]: (9) (10)Figs 4(a,b) show, the both of (1) and (2) dependence on (hЅ) for these films. The behavior of both (1) and (2) for all these studied films is the same with (hЅ), by and increase with (hЅ) for all these samples. The values of Volume Energy Loss Function (VELF) and Surface Energy Loss Function (SELF) for these films were determined optically as follow [52]: (11) (12)The relation between VELF/SELF for these thin films is shown in Fig. 5. Linear optical susceptibility ((1)) describes the response of the material to an optical wave length, ((1)) was determined using the following relation [57]: (13)The relation between ((1)) and (hЅ) for In1-xMnxSe thin films is shown in Fig.6, from this Fig. it was seen that, the linear optical susceptibility ((1)) increased with (hЅ), this means that, there is a possibility of wide change in optical properties by a slight change in composition for these samples.

3.2. Nonlinear optical propertiesAn important parameter of the non-linear optical parameters is that the nonlinear refractive index (n2), which can be explained as, when light with high intensity propagates through a medium, this causes nonlinear effects[58], n2 was determined from the following simple equation [59-60]: (14)The dependence of n2 on wavelength for In1-xMnxSe thin films is shown in Fig. 7. The values of n2 decrease with wavelength for all these studied samples. An important parameter to assess the degree of nonlinearities is the third-order nonlinear optical susceptibility ((3)), which was determined using the following equation [61]: (15)Where A is a quantity that is assumed to be frequency independentand nearly the same for all materials =1.7 x 10-10 e.s.u [61].

The third-order nonlinear optical susceptibility 3 dependance on and photon energy for In1-xMnxSe thin films with different (x) values is shown in Fig.8. It was noticed that, the behavior of ((3)) is the same for all the studied samples, the values of ((3)) increses with (hЅ), this is due to, when (hЅ) incresed the defliction of the incident ligth beam increase . On the other hand, another important nonlinear parameter such was non-lnear absorption coefficient (Іc) which, determined as follows [62]: (16) Fig. 9 shows the influence of hЅ on (Іc). It is observed that, the values of Іc increses with hЅ for all these samples as shown in Fig. 9. Because of the higher values of (hЅ), the large number number of excited electron which overcome the band gap.

3.3. Electrical results Electrical susceptibility ((e)) was determined using the following relation [63]: (17) Fig. 10 shows the electrical susceptibility ((e)) dependence on (hЅ) of these investigated samples. From this figure it is clear that, the values of ((e)) increase with (hЅ), this is due to, the electron mobility increases with (hЅ).The relative permittivity µr was calculated using the following relation [64] (18) The relation between relative permittivity (µr) and wavelength for In1-xMnxSe thin films with different (x) values is shown in Fig. 11. It is clear that, the values of (µr) increase with (hЅ) for all these samples; this could be attributed to, the electron mobility increases with (hЅ).3.4. Semiconducting and electronic resultsThe density of states (DOS) of a system describes the number of states per interval of energy at each energy level available to be occupied.

The Nv and Nc play very important rule of examination the linear optical transition and non-linear optical properties. The Nv and Nc were calculated as follow [65]:- (19) (20)Where Nv and Nc were the density of states for both valence and conduction bands respectively, effective mass of electrons m*e (InSe) = 0.14 [66], m*e (MnSe (= 0.15 [67], effective mass of holes m*h (InSe) = 0.37 [66] and K is a Boltzmann constant. The determined values for both Nv, Nc were shown in table 1. Another important factor was determined theoretically is the position of Fermi level [61]: (21)The values of Fermi level position for these investigated thin films are shown in table 1.4. ConclusionThe values of Ed and Eo for In1-xMnxSe increase with different x values (x=0.05, 0.1 and 0.15), and had the values (Ed from 4.22 to 4.80 eV) and also Eo had the values from (3.14 to 3.40 eV). The values of (N/m*) increased with x values ,which increases free carrier. The values of M-1 and M-3 also increase with increasing Mn concentration. (no) slight increase with Mn content. The both of (µ) and (µ) increases with (hЅ), the maximum values decrease with increase Mn content, due to the increase of electron mobility’s with increasing Mn ratio. Both of (1) and (2) had maximum values of from (1.17 to 1.33 eV) with increasing Mn ratio.

The ((1)) increases with (hЅ) for all compositions. The values of (n2) increases with (“) for all these samples, while ((3)) increased with (hЅ). This means that these samples had a high ability to changing its optical properties by changing wavelength and applied field. The non-linear absorption coefficient (Іc) increased with (hЅ)for these samples, also both of the ((e)) and (µr) increase with (hЅ) and had a highest value near the energy gap. The composition values (x) affected on the values of both of Nv and Nc, while Ef affected slightly with the composition values (x).

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