Letter to the Editor Electrical switching behavior of amorphous Al 23 Te 77 thin film sample Chandasree Das, R. Lokesh, G. Mohan Rao, S. Asokan ⁎ Department of Instrumentation and Applied Physics, Indian Institute of Science, Bangalore 560012, India abstract article info Article history: Received 8 April 2010 Received in revised form 28 July 2010 Available online 26 August 2010 Keywords: Electrical switching; Semiconductors; Thin films The electrical switching behavior of amorphous Al 23 Te 77 thin film devices, deposited by flash evaporation, has been studied in co-planar geometry. It is found that these samples exhibit memory type electrical switching. Scanning Electron Microscopic studies show the formation of a crystalline filament in the electrode region which is responsible for switching of the device from high resistance OFF state to low resistance ON state. It is also found that the switching behavior of thin film Al–Te samples is similar to that of bulk samples, with the threshold fields of bulk samples being higher. This has been understood on the basis of higher thermal conductance in bulk, which reduces the Joule heating and temperature rise in the electrode region. © 2010 Elsevier B.V. All rights reserved. 1. Introduction In the group of amorphous solids, semiconducting chalcogenides are interesting due to their applications in optoelectronics [1], infrared optical fibers [2], solar cells [3], optical recording systems [4], Phase Change Memories (PCM), etc. The absence of long-range order in these materials provides the convenience of changing the elemental ratio and hence the properties over a wide range. One of the most interesting as well as remarkable properties of chalcogenides which makes them suitable materials for phase change memories (PCM) is electrical switching, first observed by Ovshinsky nearly four decades ago [5]. Chalcogenide glass based phase change memories are recently being considered as a possible replacement for conventional Non Volatile Random Access memories (NVRAMs). Phase change memories make use of chalcogenide glasses of memory switching type. The main advantages of PCM are their direct write/ over write capability, lower volume operation, write /erase cycle, and easiness to integrate with logic [6,7]. The electrical switching in chalcogenide glasses occurs when an appropriate voltage, known as the threshold voltage (V T ), is applied and the glass switches to a high conducting ON state from a low conducting OFF state. This phenomenon can be divided into two general categories [8]: i) Threshold switching, in which continuous electrical power is required to maintain the high conducting ON state and ii) Memory switching, in which the ON state can be maintained without electrical power. Threshold switching is known to be electronic in nature; however, additional thermal effects come into play in memory materials, which result in the formation of a conducting crystalline channel in the electrode region [9]. Several tellurium based binary amorphous semiconductors such as As–Te, Ge–Te, Si–Te, In–Te and Ga–Te have been found to exhibit memory type of switching in their bulk form, at electrical fields of the order of 10 5 V/cm [10–17]. Ge–Te–Cu, Ge–Te–Ag, and Ge–As–Te are few examples of ternary tellurium based glasses which exhibit memory switching [18,19]. Apart from that, studies also have been done on tellurium based glasses like As–Te [20], Ge–Te [21] to know the composition dependence of crystallization and the effect of metallic doping on these glasses. Earlier investigations indicate that bulk, glassy Al x Te 100 -x samples [22], exhibit memory type electrical switching, though no such work has been found in literature on Al x Te 100 - x samples in amorphous thin film form. In this work, amorphous thin films of Al 23 Te 77 have been deposited by flash evaporation method and the I–V characteristics and electrical switching behavior of the films have been studied along with surface morphology and composition. The reasons behind choosing this particular stoichiometry are: a) It can be prepared easily in bulk glass which can be used as a base material for thermal evaporation. b) It has shown a clean memory switching in the bulk glassy form. c) The earlier investigations have indicated that the x = 23 compo- sition in the Al x Te 100 - x system corresponds to the rigidity percolation threshold [23] and interesting properties have been observed in chalcogenide glasses at compositions corresponding to the rigidity percolation threshold [24,25]. 2. Experimental techniques The base–glassy semiconductor material with composition Al 23 Te 77 has been prepared by melt quenching technique. Constituent elements (99.999% pure) are weighed to±0.1 mg accuracy and sealed in a flat Journal of Non-Crystalline Solids 356 (2010) 2203–2206 ⁎ Corresponding author. E-mail address: sasokan@isu.iisc.ernet.in (S. Asokan). 0022-3093/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2010.07.057 Contents lists available at ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol LETTER TO THE EDITOR