Optical properties of annealed As30Te67Ga3 thin films grown by thermal evaporation

Abstract

Chalcogenide glasses have received lots of attention because of their superior optical properties. To optimize these properties and expand areas of applications, more studies are required to establish the extent to which the parameters can be tuned over a wide range of annealing temperatures and heating rates. To do this, bulk and thin ∼150 nm As 30 Te 67 Ga 3 films were prepared by melt-quenching and thermal evaporation techniques, respectively. The phase transition was investigated using differential scanning calorimeter (DSC) while the crystal structures were studied by X-ray diffraction (XRD). Characteristic temperatures such as the glass transition, crystallization and melting temperature of the bulk glass were found to depend on the heating rate. The activation energy of glass transition was 167.29 kJ/mol while the energy of crystallization was 103.98 kJ/mol. XRD results indicated that the annealed films showed more crystallinity, larger average crystallite size, lower dislocation density and lower strain as annealing temperature increased. According to the Avrami exponent, a combination of two and three-dimensional crystal growth with heterogeneous nucleation are possible mechanisms for the crystallization process. Moreover, optical constants such as the optical band gap, refractive index, extinction coefficient, high-frequency dielectric constants, real and imaginary parts of dielectric constants were found to strongly depend on the annealing temperature. The optical energy gap decreased from 1.1 to 0.89 eV as the annealing temperature increased from 373 to 433 K. These results indicate that thermal annealing is a major factor that can be used to tune the crystal structure, and hence the optical properties of As 30 Te 67 Ga 3 system.

Theoretical and Experimental Parameters of the Structure and Crystallization Kinetics of Melt-Quenched As30Te64Ga6 Glassy Alloy

“…In the sense that the studied system has two stages of stability but the first stability does not last long and the studied system is more stable at the second crystallization stage. Compared to other studied compositions of As-Te-Ga glasses, the increase of Ga or decrease in Te enhances the thermal stability of the formed glass [16,[39][40][41].…”

“…The existence of a single reveals that the formed As30Te64Ga6 glass is more stable than those glasses revealing multi-. The concentration of Ga in the As-Te-Ga alloys affect the number of crystallization peaks, as there is one, or two crystallization peaks observed for the As30Te70, As30Te67Ga3, and As30Te60Ga10 glasses at different β [16,[39][40][41]. It was observed the value of characteristics temperatures are shifted to higher values as the Ga concentration increase or Te decrease at the same β.…”

“…Furthermore, the transformation from semiconductor to metal trend in the ternary glassy system As-Te-Al encourages after addition of the Al element to the As-Te system [13]. Studies of the physical properties, including the optical, electrical, and structural properties of the As-Te-Ga system is limited [11,[14][15][16][17]. For example, some efforts have been done to study the effect of heat treatment (e.g.…”

“…For example, some efforts have been done to study the effect of heat treatment (e.g. annealing) on the optical properties for few compositions of As-Te-Ga thin films [11,16,18]. To the best of our knowledge, the thermal analysis and crystallization kinetics of the As-Te-Ga system has not been extensively investigated [19].…”