Temperature Dependence of Electrical Resistance in Ge-Sb-Te Thin Films

Nowadays, the Ge-Sb-Te system is studied extensively for use in the field of both electrical and optical non-volatile memories. The key of this application is based on the changes in the physical properties (electrical conductivity or refractive index) of these films as a result of structural transformation between amorphous and crystalline states. Both states are highly stable and it is relatively easy to change between them when they are prepared as thin films. In this work, structural and electrical behaviours with the temperature of thin films with compositions Ge13Sb5Te82, Ge1Sb2Te4, Ge2Sb2Te5, Ge1Sb4Te7 and Sb70Te30 (atomic fraction) were studied. Films were obtained by pulsed laser deposition (PLD) using a pulsed Nd:YAG laser (lambda= 355 nm) and they were structurally characterized by X-ray diffraction. Temperature dependence of electrical resistance was studied for these films from room temperature to 520 K at a heating rate about 3 K/min. During crystallization, their electrical resistance falls several orders of magnitude in a narrow temperature range. The electrical conduction activation energies of the amorphous and crystalline states and the crystallization temperature were determined. The crystallization products were characterized by X-ray diffraction. The results were compared with those obtained by other authors.