Thermal properties and crystallization processes in semiconducting AlAsTe glasses

Abstract

Glasses in the Al–As–Te system are prepared and characterized. DSC and X‐ray studies of the crystallization are also performed. The kinetic parameters (activation energy and Avrami index) are obtained in non‐isothermal conditions by a method previously described. Diffusion mechanisms are responsible for the crystallization and an activation energy of about 1.5 eV is found for the diffusion of Te. The Al content is shown to increase the stability of the glasses, while high Te content favours phase separation and As contributes to the structural rigidity in these compounds. The glass forming system is found to be of technological interest.

Electrical switching and aluminium speciation in Al-As-Te glasses

“…Interestingly, the crystallization reaction is absent for x ≥ 15. Similar kind observation has been reported earlier on Al-As-Te glasses [34,35]. Glass with x = 10 has a very weak crystallization peak.…”

“…Another interesting observation is that in many of the metal doped chalcogenide glasses the crystalline phases involving metal atoms are absent. For example, in thermally crystallized Al m As n Te 100-m-n , Ge 15 Te 85-s Cu s , Ge 20 Te 80-t Sn t , glasses, there is no Al, Sn or Cu involved crystalline phases are observed [34,[38][39][40]. In the binary Al u Te 100-u (17 ≤ u ≤ 30), the formation of Φ(Al\ \Te) crystalline phase has been observed [41].…”

“…Also the energy barrier for diffusion above the softening point is weak in Te-rich glasses which makes the transition of glass to crystal extremely rapid [37]. The bond length of As\ \As (2.49 Ǻ) is very much less than the Te\ \Te (2.86 Ǻ) [34]. This makes the rotation of molecules difficult in As-rich compositions.…”

“…The concentration of Te is also critical in determining the switching type in Al-As-Te glasses. It is suggested that the Te rich glasses are not homogeneous hence upon heating they phase separate [34,35]. As\ \Te based glasses having Te N60% crystallize into As 2 Te 3 and Te.…”

Theoretical interpretation of activation energies associated with the glass transition, obtained from td or DSC experiments

“…2), which can easily be characterized by the temperature of the maximum, Tin. The shifts in the characteristic temperatures Tg and T,, when the heating rate is varied are habitually used empirically to obtain the "activation energy" corresponding to the glass transition or sub-Tg processes [14,15]. Such a procedure however, is, seldom justified in the frame of any kinetic model for processes of structural rearrangements in glasses near To.…”