Abstract

Purpose. Thin films of Sb_xSe(Te)_100−x (provided that x ≥ 50) are suitable for manufacture of the PRAM devices that work on the basis of the following reversible phase transition: “amorphous phase ↔ crystalline phase”. This paper presents results of investigations of the temperature dependences between the electrical resistance and optical transmission coefficient in the course of changes in the conditions of thermocycling and heating conditions.

Methods. Crystallization of  thin films of Sb_xSe(Te)_100−x (provided that x ≥ 50) was investigated with the help of the method, which ensures simultaneous measurements of the electrical resistance and optical transmission coefficient within one and the same sample. Investigations of the R(T) and Θ(T) dependences were performed on the planar structures “chromium layer – Sb_xSe(Te)_100−x film” within the range of temperatures from 293 K up to 493º K in the continuous mode within the range of the heating rates (q) from 3º K/min. up to 6º K/min.; in the mode of thermal cycling, as well as in the heating mode on the condition of the relevant stops of the temperature sweep at the selected stabilisation temperatures (T_st) for a certain duration of the temperature stabilisation (t_st).

Results. Nonisothermal crystallisation of the amorphous films of Sb_xSe(Te)_100−x (x≥50) is accompanied by a sharp decrease in the values of the electrical resistance and optical transmission coefficient. The transition parameters (starting temperature T_ph of the transition from the amorphous state into the crystalline one; temperature range of transition ∆T_ph; changes in the electrical resistance ∆R and optical transmission coefficient ∆Θ) depend on the chemical composition of films, as well as on the heating rate. As concerns the materials under investigation, value of the ∆T is within the range from 4º K up to 18º K, while value of the ∆R has been changed by 2 or 3 orders of magnitude. As the heating rate increases, T_ph and ∆T_ph values shift to the higher temperatures. Investigations have shown that crystallisation of the Sb_xSe(Te)_100−x amorphous films (partial or complete crystallisation) under certain conditions can occur at the temperatures below T_ph. The percentage share of the crystallised volume of films and values of R, Θ, ∆R, and ∆Θ depend on the temperature parameters and time-based parameters (for example, T_st, t_st) of the heating process. 

Conclusions. It is established that Sb_xSe(Te)_100−x (x≥50) amorphous films crystallise under certain conditions of heating. The phase transition from the amorphous state to the crystalline one is accompanied by a sharp decrease in the electrical resistance and optical transmission coefficient. The crystallisation processes and phase transition parameters depend on the chemical composition of films and on the heating conditions. The results testify that Sb_xSe(Te)_100−x films can be used as the materials for manufacture of the temperature detectors and PRAM devices

Keywords: chalcogenide materials, amorphous films, phase transitions, crystallisation, memory cells, temperature detectors

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