Ga 80-x Se x Te 20 amorphous system was prepared by conventional technique. Structural, morphology and optical properties have been investigated. X-ray diffraction (XRD) patterns reveal the non-crystalline nature of the prepared sample. Differential thermal analysis (DTA) traces indicate the presen ce glass transition temper a ture Tg for all samples below 500°C. Addition Tg values increases by increas ing Se content. Energy dispersive X-ray spectroscopy (EDX) data shows good agreement with actual composition. Moreover , surface characterization was achieved by scanning electron microscope (SEM) . The patterns confirmed the non-crystalline nature. In order to analyze the data , the cohesive energy C.E w as calculated by all three composition optical properties that have been investigated in the wavelength range 500 - 2500 nm. Reflectivity R and transmitivity T spectrum were used to estimate the band gap energy using UV-Visible absorption spectrum. It is worthy mention that the optical band gap follows the Tg and cohesive energy behavior, where it increases by increasing Se content.
Chalcogenide glasses find wide applications in various fields of up-to-date technology due to their peculiar properties [
Bulk amorphous of Ga80−xSexTe20 (where x = 10, 15 and 20 at %) chalcogenide glass were prepared by conventional melt quenching technique [
The x-ray diffraction machine (XD-D ShimadZu) was used to study nature of the prepared sample). Moreover the scanning electron microscope (Joel-SEM-5400) which connected by energy dispersive spectroscopy (EDX) technique was used to study the morphology together with chemical compositions of samples, constitutes fully quantitative analyses results were obtained from the spectra by processing date through Zaf correction program. The transmittance and reflectance were measured using a double beam UV-VIS Spectrophotometer in the wavelength range 500 - 2500 nm.
The X-ray diffraction pattern of theGa80−xSexTe20 (where x = 10, 15 and 20 at %) glass composition was presented in
Morphological inspections performed by SEM on as-grown films have shown a flat surface without the presence of cracks agglomerates and precipitated
The possible bonds formed in chalcogenids system Ga80−xSexTe20 are Se-Ga, Se-Se, Se-Te. According to chemical bond approach (CBA) [
The bond energy E(A-B) of hetero nuclear bond, can be calculated by Equation [
E A − B = ( E A − A − E B − B ) 1 / 2 + 30 ( x A − x B ) 2 (1)
EA−A and EB−B are the bonds energies of homo nuclear bonds, xA and xB are electronegativity values of A and B Elements.
The bond energy of the homo polar bonds EGa−Ga is 31.82, ESe−Se is 44, and ETe−Te is 33 Kal/mol [
The electronegativity value are 1.81, 2.55, and 2.10 for Ga, Se and Te respectively [
By using Equation (1) values of EGa−Se, ESe−Te and ETe−Se are gives as 53.85, 44.93 and 44.18 respectively.
The bonds are formed in order of decreasing bond energy.
Ga-Se bonds having maximum energy are first followed by ETe−Se then EGa−Te bonds.
As these bond energies are assumed to be addition, so cohesive energies calculated by summing the bond energies over all possible in a compound. Cohesive energies calculated as:
C E = ∑ C i E i (2)
where Ci is the probability of formation of expected bonds, and Ei is the energy of the corresponding bond present in the system.
Composition | Electronegativity | Distribution of chemical bonds | Cohesive energy | ||
---|---|---|---|---|---|
Ga-Se | Ga-Te | Ga-Ga | CE ev | ||
Ga70Se10Te20 | 1.81 | 0.09523810 | 0.1904762 | 0.7143857 | 1.496454 |
Ga65Se15Te20 | 2.55 | 0.1538462 | 0.2051282 | 0.6410256 | 1.5544054 |
Ga60Se20Te20 | 2.10 | 0.2222222 | 0.2222222 | 0.5555556 | 1.6220154 |
It is observed that by increasing Se content leads to increasing the cohesive energy in chalcogenide system Ga80−xSexTe20.
Optical properties of Ga80−xSexTe20 (where x = 10, 15 and 20 at %) have been investigated in the wavelength (500 - 2500) nm. Figures 5(a)-(c) show reflectivity R and transmition T of investigated then films with wavelength.
The data of (
The obtained spectra were used to estimate the optical band gap energies as 0.721 ev, 0.97 ev, and 1.007 ev for Ga70Se10Te20, Ga65Se15Te20 and Ga60Se20Te20 respectively.
It is worthy to mention that the band gap increases by increase Se content, i.e. by increasing C.E the letter represent the average binding energy of the system.
Glassy system of Ga80−xSexTe20 (where x = 10%, 15% and 20%) Chalcogenide Semiconductors has been successfully prepared. The study includes DTA, XRD, SEM, EDX and UV-visible absorption spectrum. The analysis of DTA reveals the absence of any sharp exothermic peak indicating the absence of structural change, which is in a good agreement with X-ray diffraction, confirmed the amorphous state of the system. Also (SEM) and (EDX) are confirmed the absence of serious phase. Moreover, the cohesive energy of the investigated has been calculated by using chemical bond. It follows the Tg behavior, and by increasing Se content, cohesive energy increases.
Addition of selenium content in the Ga80−xSexTe20 system modifies the properties of the present sample especially the optical (T & R). Optical measurements indicate that the non-direct transition is dominant in mechanism responsible for the photon absorption inside the investigated samples. It is also observed that the increasing of Se content leads to increase of band gap. This is in fair agreement with Tg and cohesive energy data.
Al Mokhtar, K.M. and Alsobhi, B.O. (2017) Structural, Morphology and Some Optical Properties of Chalcogenide Ga80−xSexTe20 (Where x = 10%, 15% and 20%) Glassy Material. New Journal of Glass and Ceramics, 7, 91-99. https://doi.org/10.4236/njgc.2017.74008