Kinetics of crystallization in a.Se80In20-xPbx under isothermal annealing: Activation energy determination

Abstract

In the past few years research on phase change optical data storage media has concentrated on increasing the erase speed. The chalcogenide glasses have been the subject of extensive investigation due to their interesting properties. The most widely exploited property of chalcogenide glasses is their large infrared transmittance in combination with their chemical and mechanical durability. The most unique property of chalcogenides glasses is that they are semiconducting in the amorphous phase, and they can become highly conductive in the crystallization phase, hence the electrical switching ability. In addition, crystalline chalcogenide can be much more reflective than amorphous chalcogenides. In recent years, efforts have been made to develop chalcogenide based erasable optical storage media. Since the write and erase time is closely related to the melting temperature (Tm) and the speed of crystallization, a detailed investigation of the compositional dependence and of the effect of a small quantity of additive on crystallization is necessary [1]. There are many methods of activation energy determination from the isothermal experiments. All of them can be divided in two groups: local and global methods. Local methods use only certain points from the experimental curve obtained during isothermal annealing. In the global method, which has been presented in many papers [2, 3], a general scaling factor is used to make the experimental curves obtained for different annealing temperature collapse into a single temperature-independent curve. Another method, which is also quite convenient for crystallization measurement, because of its simplicity and accuracy of continuous measurements, is conductivity measurements [4, 5]. This method was used in our experiment. The aim of the present work is to study the isothermal crystallization kinetics by using conductivity measurements and to discuss the effect of Pb on the crystallization of a Se-In alloy. Since the conductivity of the amorphous state is much lower than that of the crystalline state, the electrical measurements are expected to be sensitive to phase changes in these materials [6]. The selection of Se is because of its wide commercial applications. Its device applications like switching, memory and xerography, etc., made it attractive. It also exhibits [7] a unique property of reversible transformation. This property makes very useful in optical memory devices. But in the pure state it has disadvantages because of its short lifetime and low sensi-