Electrical resistance measurements of Ge13Sb5Te82 thin films

J. A. ROCCA; M. FONTANA; B. ARCONDO

Valparaíso

Congreso; Reunión Nacional de Sólidos 2009; 2009

One of most important properties of sometellurium-based chalcogenide glasses is theoptical and electrical switching between twostates: the glass and the crystalline state. Forexample, Ge-Sb-Te amorphous films are widelyused in rewritable compact disks (CD-RW),digital versatile disks (DVD-RW) and are foundto be suitable for electrical memories (i.e.: non-volatile memories).In a previous work [1], we have foundthat the glass forming ability of Ge-Sb-Tesystem, for rapid solidification from the liquid,is restricted to a small composition range nearthe binary eutectic Ge 15 Te 85 . The crystallizationof Ge 13 Sb 5 Te 82 amorphous samples is mainlygoverned by the crystallization of Te phase,observing the appearance of the stablehexagonal phase Ge 2 Sb 2 Te 5 as secondarycrystallization.Thecrystallizationpeaktemperature is 190 °C at a heating rate of 5 K/mIn this work, thin films of compositionGe 13 Sb 5 Te 82 were obtained by means of PulsedLaser Deposition (PLD) technique employingbulk glassy targets. Films of thickness between200 and 500 nm were deposited on glasssubstrates employing a Nd:YAG laser (λ=355nm). The temperature dependence of electricalresistance in these Ge 13 Sb 5 Te 82 thin films hasbeen studied.The films are put into a conventionalfurnace in vacuum upon a heating rate ofapproximately 1.8 K/m. A typical measurementof the film resistance is shown in Fig. 1.We can observe a great change in theresistance in a small temperature range130-170 °C: the resistance falls three orders ofmagnitude. This fact can be associated with thinfilm crystallization. However, thin filmcrystallization is different to that of bulksamples. Both, crystallization temperature andcrystalline products are different.At room temperature, the resistance ofcrystallized films is six orders of magnitudelower than in the amorphous state. Thisresistance change indicates that Ge 13 Sb 5 Te 82composition film can be exploited for non-volatile memories applications.Both amorphous and crystalline phasesshow semiconductor behaviour.References:[1] J. Rocca et al., Journal of Non-CrystallineSolids355(2009)2068?2073doi: 10.1016/j.jnoncrysol.2008.10.020