Electrical resistance measurements of Ge13Sb5Te82 thin film

J.ROCCA; M.FONTANA; B.ARCONDO

Valparaiso, Chile

Workshop; Solidos 2009; 2009

One of most important properties of some tellurium-based chalcogenide glasses is the optical and electrical switching between two states: the glass and the crystalline state.  For example, Ge-Sb-Te amorphous films are widely used in rewritable compact disks (CD-RW), digital versatile disks (DVD-RW) and are found to be suitable for electrical memories (i.e.: non-volatile memories). In a previous work [1], we have found that the glass forming ability of Ge-Sb-Te system, for rapid solidification from the liquid, is restricted to a small composition range near the binary eutectic Ge15Te85. The crystallization of Ge13Sb5Te82 amorphous samples is mainly governed by the crystallization of Te phase, observing the appearance of the stable hexagonal phase Ge2Sb2Te5 as secondary crystallization. The crystallization peak temperature is 190 °C at a heating rate of 5 K/m. In this work, thin films of composition Ge13Sb5Te82 were obtained by means of Pulsed Laser Deposition (PLD) technique employing bulk glassy targets. Films of thickness between 200 and 500 nm were deposited on glass substrates employing a Nd:YAG laser (l=355 nm). The temperature dependence of electrical resistance in these Ge13Sb5Te82 thin films has been studied. The films are put into a conventional furnace in vacuum upon a heating rate of approximately 1.8 K/m. A typical measurement of the film resistance is shown in Fig. 1. We can observe a great change in the resistance in a small temperature range 130-170 °C: the resistance falls three orders of magnitude. This fact can be associated with thin film crystallization. However, thin film crystallization is different to that of bulk samples. Both, crystallization temperature and crystalline products are different.The crystalline phase resistance at room temperature is six orders of magnitude lower than in the amorphous state. This resistance change indicates that Ge13Sb5Te82 composition film can be exploited for non-volatile memories applications. Both amorphous and crystalline phases show semiconductor behaviour.