EFFECT OF Cd ADDITION ON THE AC CONDUCTIVITY AND DIELECTRIC PROPERTIES OF Ge70Te30 FILMS (original) (raw)
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DC AND AC CONDUCTIVITY MEASUREMENTS ON Ge2Sb2Te5 FILMS
Thin films of Ge2Sb2Te5 were prepared using thermal evaporation technique. The amorphous structure and stoichiometery of the films were identified by X-ray diffraction and Energy Dispersive X-ray analysis, EDX. The conductivity measurements were carried out using DC I-V curves and AC Impedance spectroscopy techniques. The measured activation energy (Ev) is found to be about 0.36-0.39 eV, respectively, which is approximately half the energy gap (Eg= 0.72-0.78 eV). The amorphous-crystalline transition temperature (Tc) of the films was also estimated to be 135 o C. The results can be Phase change materials based on chalcogenide alloys are found to be suitable for optical and electrical memories due to its fast crystallization. The operation principle of these devices is based on the ability of the active materials to reversibly transform between amorphous and crystalline phases. Among these alloys, Ge2Sb2Te5 exhibits the best performance when used in DVD-RAM in terms of speed and stabi...
Thin films of thickness in the range of 500 -3000 A° of the composition Ge 20 As 30 Se X Te (50-X) (with x = 0 and 40) were prepared by thermal evaporation. D.C. conductivity was reported for the investigated films. It was found that the activation energy decreases by increasing the thickness of the film. It was observed that the increase of Se was followed by increase in the glass transition temperature. Also, it is noticed that increasing Se content affected the average heat of atomization and cohesive energy (C.E.) of the composition and the energy gap decreases by increasing Se content.
Semiconductors, 2011
Chalcogenide glassy semiconductors of the ternary system Ge-Se-Te along the Ge 10 (Se-Te) 90 and Ge 30 (Se-Te) 70 joins have been synthesized. The crystallization ability, near IR transmission spectra, and temperature dependence of the electrical conductivity of the alloys obtained have been studied. It is shown that chalcogenide glassy semiconductors along the Ge 10 (Se-Te) 90 join have a lower softening and crystalli zation points compared with semiconductors belonging to the Ge 30 (Se-Te) 70 join. A change in the electrical conductivity of samples by several orders of magnitude occurs upon a phase transition from the glassy to the crystalline state. Compositions of chalcogenide glassy semiconductors in the Ge-Se-Te system are found, which have α < 1 cm-1 absorption coefficient at wavelengths of λ ≈ 1.5 μm and exhibit a thermally induced phase transition from the glassy to the crystalline state.
Structural and electrical properties of Germanium-doped Sb70Te30 eutectic thin films
Journal of Non-Crystalline Solids, 2011
Ge-doped Sb 70 Te 30 eutectic films show high potential for high transfer rate recording and non-volatile memory applications. Their potential applications are based on the difference in optical and electrical properties between the crystalline and amorphous phases. However, the structure and crystallization mechanism of such films is not yet well understood. The aim of this work is to study the amorphous-to-crystalline phase transformation mechanism in eutectic thin films of pure Sb 70 Te 30 and doped with 2, 5 and 10 at% of Ge. Results of isokinetics and isothermal annealing were carried out using various techniques: four-probe electrical, optical reflectance and X-ray measurements. The results of optical and electrical measurements of Ge doped Sb 70 Te 30 eutectic films showed that the addition of Ge increases both, the crystallization temperature and the effective activation energy of crystallization and that the mechanism of crystallization does not depend on Ge contents. In amorphous films, Ge acts as impurity center and does not affect the optical band gap value, but decreases the pre-exponential factor in the thermally activated conductivity. In crystalline films, Ge is probably incorporated into the Sb 70 Te 30 structure and Ge vacancy are responsible for p-type metallic conduction, which increases with increasing the Ge content.
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Electrical conductivity of Ge10 Se90-x Bix (x=0,2,4,6,8,10) glassy systems prepared by melt quenching technique has been studied at different temperature in bulk form through I-V characteristic curves. It has been observed that the electrical conductivity increases as the Bi concentration increases up to 4 atomic weight percentages and on further addition of Bi it reduces. The variation in electrical conductivity with Bi concentration is attributed to the Se-Bi bond concentration. Using the Arrhenius equation of conductivity, the activation energy of conduction is evaluated. The effect of Bi concentration on activation energy has also been studied. It is quite evident from results that Poole-Frankel and Rechardson-Schottky conduction mechanism hold good for conduction in these glasses.
Optical properties and DC electrical conductivity of Ge28−xSe72Sbx thin films
Vacuum, 2006
Thin films of Ge 28Àx Se 72 Sb x (x ¼ 0, 8, 16, 24 at%) with thickness of 200 nm are prepared by thermal evaporation onto glass substrates under vacuum of 5.3 Â 10 À5 mbar. Optical reflectance and transmittance of these films are measured at room temperature in the light wavelength region from 200 to 1100 nm. The estimated optical energy gap, E g , is found to decrease from 2 eV (0 at% Sb) to 1.5 eV (24 at% Sb), whereas the band tail width, E e , increases from 0.062 to 0.077 eV, respectively. The refractive index, n, and extinction coefficient, k, are determined as functions of wavelength. The DC electrical conductivity, s, of films is measured as a function of temperature in the range from 300 to 360 K. The extracted value of activation energy, DE, is found to decrease from 0.95 eV (0 at% Sb) to 0.74 eV (24 at% Sb). Optical and electrical behavior of films can be explained in terms of cohesive energy (CE) and Se-Se defect bonds. r
Ac conductivity and dielectric properties of Ga2S3–Ga2Se3 films
The ac conductivity and dielectric properties of amorphous Ga 2 S 3 -Ga 2 Se 3 solid solution in thin film form have been studied in the temperature range from 306 to 403 K and in the frequency range from 10 2 to 10 5 Hz. The ac conductivity was found to be proportional to o s . The exponent s was found to be 0.997 at room temperature and decreased with increasing temperature. It was found also that ac activation energy DE(o) has small values, which decreased with increasing frequency. It was found that relaxation time t was 5.2 Â 10 À5 s. These results were interpreted in terms of the correlated barrierhopping model. It was found also that the dielectric constant e 1 and dielectric loss e 2 decreased with the increase of frequency, while they decreased with increasing temperature in the investigated ranges. The calculated value of the barrier height W m (0.485 eV) according to the Guintini equation agreed with that proposed by the theory of hopping of charge carriers over a potential barrier.
Electrical and optical investigations in Te–Ge–Ag and Te–Ge–AgI chalcogenide glasses
Journal of Alloys and Compounds, 2015
a b s t r a c t (GeTe 4 ) 100Àx Ag x and (GeTe 4 ) 100Àx (AgI) x glasses were prepared by a melting-quenching method. The glass electrical conductivity was investigated by both electrochemical impedance spectroscopy at different temperatures from 283 K to 333 K and four-probe method at room temperature (293 K). Meanwhile, as a major factor determining the electrical conductivity of a solid, optical band gap was also studied. By comparing the electrical conductivity values and glass optical band gap evolution, it was found that (GeTe 4 ) 100Àx Ag x glasses are mainly electronic conductive. On the other hand, the electrical conductivities of (GeTe 4 ) 100Àx (AgI) x glasses firstly show a monotonic decrease by increasing AgI up to 15 mol.%, and then an increase when the AgI content is higher than 15 mol.%. The activation energy E a and the pre-exponential factor r 0 show apparent turning point when AgI content is 15 mol.%, signifying a conductivity mechanism change. In this paper, correlations between the conductivity and hypothetical structures in (GeTe 4 ) 100Àx Ag x and (GeTe 4 ) 100Àx (AgI) x glasses are done and the importance of the Ag role is underlined.