Effect of impurity (Te and Zn) incorporation in the density of defect states in thin films of Se 90 In 10 and Se 75 In 25 glassy alloys N. Sharma, S. Kumar ⁎ Department of Physics, Christ Church College, Kanpur, U.P. (208001) India abstract article info Article history: Received 3 May 2011 Received in revised form 8 August 2011 Available online 8 September 2011 Keywords: Chalcogenide glasses; Thin films; SCLC; DOS In this paper we report the effect of Te and Zn incorporation on the density of defect states of two binary Se– In glassy systems. For this purpose, we have chosen here two well known Se 90 In 10 and Se 75 In 25 binary glassy alloys. Thin films of Se 90 In 10 , Se 75 In 25 , Se 75 In 10 Te 15 and Se 75 In 10 Zn 15 glassy alloys prepared by quenching method, were deposited on glass substrate using thermal evaporation technique. Current–voltage character- istics have been measured at various fixed temperatures in the thin films under study. Ohmic behavior was observed at low electric fields while at high electric fields current becomes superohmic. An analysis of the ex- perimental data confirms the presence of space charge limited conduction in Se 90 In 10 , Se 75 In 10 Te 15 and Se 75- In 10 Zn 15 glassy alloys. It was found that the absence of space charge limited conduction in Se 75 In 25 may be due to joule's heating at high fields. By applying the theory of space charge limited conduction, the density of defect states near Fermi level was calculated. The peculiar role of the additives (Te and Zn) in the pure bi- nary Se 90 In 10 and Se 75 In 25 glassy alloys is also discussed in terms of electro-negativity difference between the elements involved. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The researchers are involved in the study of electrical properties of chalcogenide glasses to explore the new dimensions for their end user applications with enhanced properties over the last four de- cades. Studies on amorphous chalcogenide glasses and thin films have attracted the attention of many researchers [1–3] in the recent years because of the challenging aspects of new concepts dealing with the mechanisms of photo-induced phenomena. Due to the need of higher photo-sensitivity at low bias voltage in photoconduc- tor applications, some semi conducting chalcogenides have been re- cently used. Amorphous Se has been investigated extensively due to its wide commercial applications like photocells, rectifiers, xerography and switching memory, etc. which made it very attractive in the field of devices. The generally accepted structure model of amorphous Se in- cludes [4] two molecular species, meandering chains, which contain helical chains of trigonal Se and Se 8 ring molecules of monoclinic Se. The effect of the addition of various elements (S, Te, As, Ge, In) on the structure of Se showed that, about 40% of the atoms have a ring structure and 60% of the atoms are bonded as polymeric chains [5]. Among these Se based glassy alloys; Se–In alloy has received much at- tention more recently because of their potential applications in solar cells and photovoltaic sensors [6,7]. Se–In belongs to the VIB–IIIA group of semi conducting com- pounds with a crystallographic structure similar to that of Se–Ga [8]. Since network connectivity, rigidity and nature of bonding do play important roles in electronic conduction process, It has been reported by several authors that when In atoms are incorporated, they probably dissolved in the Se chains increasing relatively the number of Se 8 rings while the number of Se–Se long chain decreases. At higher percentage of In it enters into the Se 8 rings. [9–11]. The effect of incorporation of third element in binary chalcogenide glassy alloys is generally accompanied by a marked change in their electrical and photoelectrical properties. It has always been an inter- esting problem in getting relatively stable glassy alloys as well as to change the conduction from p to n as most of these glasses show p type conduction only. In Ge–Se and Se–In systems, some metallic ad- ditives have been found [12–16] to change conduction from p type to n type and hence these binary systems are of great importance. Thus it is interesting to study the effect of some metallic additives on the electrical properties of the Se–In glassy system. The effect of impurity on density of defect states (DOS) has always been a subject of curiosity, as the knowledge of this parameter is a key factor in chalcogenide glasses for determining the semi conduct- ing properties of these materials. One of the most useful methods for the determination of DOS involves the measurement of space charge limited conduction (SCLC). In chalcogenide glasses, the DOS reported by different authors [17–20] ranges from 10 13 to 10 17 eV -1 cm -3 . In our earlier measurements we have reported [21] the composition de- pendence of the density of defect states in Se 75 In 25 - x Pb x (0 ≤ x ≤ 10) glassy system and used SCLC as a tool for measuring the DOS. The Journal of Non-Crystalline Solids 357 (2011) 3940–3943 ⁎ Corresponding author. Tel.: + 91 512 2573069. E-mail address: dr_santosh_kr@yahoo.com (S. Kumar). 0022-3093/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jnoncrysol.2011.08.012 Contents lists available at SciVerse ScienceDirect Journal of Non-Crystalline Solids journal homepage: www.elsevier.com/ locate/ jnoncrysol