Electrical conduction mechanism in amorphous Se 80 In 20x Pb x films M.A. Majeed Khan, M. Zulfequar, M. Husain * Department of Physics, Jamia Millia Islamia, New Delhi 110025, India Received 24 June 2002; accepted 29 August 2002 Abstract DC conductivity measurements on thin films of a-Se 80 In 20x Pb x (where x ¼ 0, 2, 6 and 10) are reported in the temperature range 200–400 K. The density of states near the Fermi level is calculated using the DC conductivity (Mott parameters). The conduction in the low-temperature region is found to be due to variable range hopping while that in the high-temperature region is due to thermally assisted tunneling of the carriers in the localized states near the band edge. Ó 2002 Elsevier Science B.V. All rights reserved. PACS: 73.61.)p; 72-15.C Keywords: Density of states; DC conductivity; Amorphous semiconductor; Thin films 1. Introduction Chalcogenide glasses have attracted much attention because of their potential application in solid-state devices. Impurity effects in chalcogenide glasses may have importance in fabricating glassy semiconductors. Moreover they are interesting as core materials for op- tical fibers for transmission especially when short length and flexibility are required [1–4]. The current interest in chalcogenide materials centers on X-ray imaging [5] and photonics. The investigation of electrical [6–9] and optical [6,7,10–12] properties of amorphous InSe thin films have been a subject of active research for both solid-state physicists and electronic engineers for their applications as photovoltaics [13,14] and memory switching [15,16] materials. Many amorphous semiconducting glasses, in particular selenium, exhibit [17] a unique property of reversible transformation. This property makes these glasses very useful in optical memory devices. However, the shortcoming of pure glassy selenium for its practical applications includes its short lifetime, low sensitivity and thermal instability. To overcome these difficulties certain additives are used and especially the use of Se– Te, Se–Sb and Se–In binary alloys is of interest owing to their various properties like greater hardness, higher sensitivity, higher crystallization temperature, higher conductivity and smaller ageing effects as compared to pure amorphous selenium [9]. The energy band gap of amorphous Se–In is about 1.3 eV at 300 K [14]. This value is close to the theoretical optimum for solar energy conversion and several attempts have already been made to utilize them in solar cells [18]. The effect of an impurity in an amorphous semicon- ductor may be widely different, depending upon the conduction mechanism and the structure of the material [19]. While in crystalline semiconductors the effect of a suitable impurity is always to provide a new donor or acceptor states, this is not essential in amorphous semiconductor [20]. Instead of providing a localized impurity level in the forbidden gap, an impurity may merely alter the mobility of the charge carries or may introduce structural change [21] in the amorphous ma- terial with or without modification of the localized states in the forbidden gap. Investigations of the temperature dependence of conductivity, the effect of impurities on the activation energy, and the effect of high electric field on the conduction mechanism is a subject of great in- terest, because the results of such studies provide ways to control effectively the conductivity of amorphous semiconductors. In the present work, the electrical properties of chalcogenide glasses in the system Se–In–Pb have been Current Applied Physics 2 (2002) 401–406 www.elsevier.com/locate/cap * Corresponding author. Tel.: +91-11-6328332; fax: +91-11- 6840229. E-mail address: mush_phys@rediffmail.com (M. Husain). 1567-1739/02/$ - see front matter Ó 2002 Elsevier Science B.V. All rights reserved. PII:S1567-1739(02)00148-7