Switching phenomenon in TlGaSe 2 layered semiconductor MirHasanYu. Seyidov a,b,⇑ , Rauf A. Suleymanov a,b , Ertan Balaban c , Yasin S ßale a a Department of Physics, Gebze Institute of Technology, 41400 Gebze, Kocaeli, Turkey b Institute of Physics Azerbaijan National Academy of Sciences, AZ – 1143 Baku, Azerbaijan c TUBITAK-BILGEM, Scientific and Technical Research Council of Turkey, Gebze, Kocaeli 41470, Turkey article info Article history: Received 31 May 2013 Received in revised form 13 January 2014 Accepted 2 February 2014 The review of this paper was arranged by Prof. S. Cristoloveanu Keywords: Switching effect Disordered semiconductors Ferroelectric–semiconductor Incommensurate phase abstract Electrical switching phenomenon was observed in TlGaSe 2 layered ferroelectric–semiconductor applying different types of electrodes on different TlGaSe 2 samples in both directions parallel and perpendicular to the pane of the layers. The non-linear current–voltage (CV) characteristics were measured by sweeping the current while measuring the voltage drop and could be classified as current-controlled S-type negative resistance phenomenon. The effects of temperature, illumination and as well as long time annealing within the incommensurate phase on the switching characteristics were also been studied. The switching phenomenon is discussed on the basis of the models widely used for disordered semicon- ductors. It was shown that TlGaSe 2 crystal demonstrates the peculiar behavior that is typical to chalcogenide glassy semiconductors (CGS). Ó 2014 Elsevier Ltd. All rights reserved. 1. Introduction The current-controlled electrical switching from the high resis- tance semiconducting off-state to the conducting on-state in CGS is a well-known phenomenon discussed in various review articles (see, for example [1–5]). Different mechanisms have been pro- posed to explain the electrical switching in CGS. These include pure electronic, thermal and mixed electronic-thermal mechanisms. It is believed that switching may be purely thermal only in bulk sam- ples whereas in thin-film samples, the role of electronic processes is crucial. It was shown in recent investigations [2,3] that ioniza- tion of the so called U-centers which is characteristic of CGS in strong electric fields increases the free-carrier concentration and causes a strong nonlinearity in the current–voltage characteristics. Joule heating increases the temperature of the specimen which in- creases the concentration of the free-carriers and leads to switch- ing to the conductive state. The family of Tl-based ternary dichalcogenide semiconductors, which have layered or chain structure has been in the focus of researchers for decades, which are mainly because of the presence of structural phase transformations. Several examples of low-dimensional dichalcogenide semiconductors, such as quasi- one-dimensional chain TlInSe 2 [6], TlInTe 2 [7], TlGaTe 2 [8] and quasi-two-dimensional layered TlGaS 2 [9] have been found to ex- hibit electrical switching. Ternary thallium dichalcogenide TlGaSe 2 is known as a ferro- electric–semiconductor which has a layered crystalline structure and undergoes the thermally stimulated phase transitions [10–12] at temperatures lower than 120 K. It is a native p-type semiconductor and has band gap energy 2.2 eV at the room temperature. Several reports discussed the transport mechanisms in TlGaSe 2 layered semiconductor [13–15]. The considerable inter- est remains regarding the mechanism of the current flow in the low-temperature region, especially below 220 K, where hopping conductivity is the main transport mechanism. Recent investigations on these crystals revealed some unusual physical properties [13,16–19]. One of the most interesting proper- ties among these is the existence of large internal electric fields. These fields appear through the specific disorder phase which is observed within the wide temperature range below 200–220 K [12,16–19]. It is suggested that deep impurity states are responsi- ble for such disorder, which strongly affects the electrical proper- ties of this compound. The role of internal electric fields is extremely important as they can influence even thermal expansion processes, thus making TlGaSe 2 crystals very sensitive to external perturbations such as illumination, external electric fields and annealing procedure [16,17]. Note that the effects of internal electric fields which were outlined above are mostly pronounced in the temperature region T > 140 K that is out of the temperature range of known phase transitions in this crystal. http://dx.doi.org/10.1016/j.sse.2014.02.001 0038-1101/Ó 2014 Elsevier Ltd. All rights reserved. ⇑ Corresponding author at: Department of Physics, Gebze Institute of Technology, 41400 Gebze, Kocaeli, Turkey. Tel.: +90 262 605 1329; fax: +90 262 653 8490. E-mail address: smirhasan@gyte.edu.tr (M. Seyidov). Solid-State Electronics 94 (2014) 39–43 Contents lists available at ScienceDirect Solid-State Electronics journal homepage: www.elsevier.com/locate/sse