Rapid Communication Structural change of laser-irradiated Ge 2 Sb 2 Te 5 films studied by electrical property measurement Sun Huajun * , Hou Lisong, Wu Yiqun, Wei Jingsong Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, No. 390, Qinghe Road, Jiading, Shanghai 201800, China article info Article history: Received 31 March 2008 Received in revised form 12 August 2008 Available online 28 October 2008 Keywords: Amorphous metals, metallic glasses Alloys Amorphous semiconductors III–V Semiconductors Crystallization Glass ceramics Conductivity Films and coatings Sputtering Glass transition Radiation effects Laser–matter interactions Microcrystallinity Phases and equilibria Structure Long range order Short-range order Structural relaxation X-ray diffraction abstract Sheet resistance of laser-irradiated Ge 2 Sb 2 Te 5 thin films prepared by magnetron sputtering was mea- sured by the four-point probe method. With increasing laser power the sheet resistance undergoes an abrupt drop from 10 7 to 10 3 X/h at about 580 mW. The abrupt drop in resistance is due to the structural change from amorphous to crystalline state as revealed by X-ray diffraction (XRD) study of the samples around the abrupt change point. Crystallized dots were also formed in the amorphous Ge 2 Sb 2 Te 5 films by focused short pulse laser-irradiated, the resistivities at the crystallized dots and the non-crystallized area are 3.375 Â 10 À3 and 2.725 X m, sheet resistance is 3.37 Â 10 4 and 2.725 Â 10 7 X/h respectively, deduced from the I–V curves that is obtained by conductive atomic force microscope (C-AFM). Ó 2008 Elsevier B.V. All rights reserved. 1. Introduction Phase-change materials based on chalcogenide alloys are found to be suitable for optical and electrical memories due to its fast reversible crystallization. The operation principle of these devices is based on the ability of the active materials to undergo very fast reversible transformation between amorphous and crys- talline phases which go with big changes of optical and electrical property [1]. Among these alloys, Ge 2 Sb 2 Te 5 exhibits the best per- formance indicated by extensive experimental studies using dif- ferent methods, such as atomic force microscopy (AFM) [2], transmission electron microscopy (TEM) [3], differential scanning calorimetry (DSC), X-ray diffraction (XRD) [4–6], Raman spectros- copy [7] and coherent phonon spectroscopy [8]. But most of these studies used the thermal-induction method to crystallize the Ge 2 Sb 2 Te 5 phase-change material, the structural and electrical changes of laser-irradiated Ge 2 Sb 2 Te 5 films is lack. The heating rate of a pulse laser can reach 10 10 °C/min [9], therefore laser- irradiation of the amorphous Ge 2 Sb 2 Te 5 thin films could embody truly the process of structural change in the films than thermal- induced crystallization. In this work, we examined the crystalliza- tion behavior and electrical property of Ge 2 Sb 2 Te 5 phase-change films using laser beam of Hitachi Computer Peripherals POP120- 5F initializer at various laser powers, van der Pauw Measurement system, XRD, respectively. The resistance and I–V curves of the fo- cused-short-pulse-laser-crystallized dots and non-crystallized area also were studied to confirm the structure of Ge 2 Sb 2 Te 5 phase-change films for the first time. Mytilineou and Ovshinsky [10] tried to realize electrical–optical hybrid cognitive behavior, but they could not achieve the course of focused pulse laser in- duced phase-change to form a conductive path. This paper dedi- cated to study structural change of laser-irradiated Ge 2 Sb 2 Te 5 films by electrical property measurement. 0022-3093/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2008.09.018 * Corresponding author. Tel.: +21 69918592. E-mail address: hjsun@siom.ac.cn (S. Huajun). Journal of Non-Crystalline Solids 354 (2008) 5563–5566 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/locate/jnoncrysol