Determination of trap depth and trap density in Se 70 Te 30x Zn x thin films using thermally stimulated current measurements S. Yadav, R.K. Pal, S.K. Sharma, A. Kumar à Department of Physics, Harcourt Butler Technological Institute, Kanpur, India article info Article history: Received 9 January 2009 Received in revised form 7 February 2009 Accepted 12 April 2009 Keywords: Chalcogenide glasses Thermally stimulated currents Trap depth and trap density abstract In the present paper concentration of traps (N t ) and trap depth (E t ) have been calculated by thermally stimulated current (TSC) measurements in amorphous Se 70 Te 30x Zn x (x ¼ 2, 4) thin films. These measurements are carried out at three different heating rates. It is observed that the amount of thermally stimulated current gradually increases and the temperature (T m ), at which maxima in TSC occurs, shifts to higher temperatures with increasing heating rates (b) as expected. The trap depth is found to be quite different for x ¼ 2 and x ¼ 4. The concentration of traps also increases slightly at higher concentration of Zn. & 2009 Published by Elsevier B.V. 1. Introduction Chalcogenide glasses are well-known promising materials for variety of photonic applications such as ultra fast optical switches, frequency converters, optical amplifiers, infrared lasers. The interest in these materials stems principally from their low phonon energy, extended infrared transparency, high refractive index, high photosensitivity, good chemical durability and special second/third order optical non-linearity [1–7]. Among these glasses, Se–Te alloys have gained much importance because of their superiority over amorphous Se. Alloying of Se with Te reduces the electronic band gap of Se thus becoming useful in a photoreceptor having more desirable spectral response for xerographic purposes [8]. Various additives have been used as third element to improve the thermal stability of binary Se–Te alloys. Recently, Zn based chalcogenide glasses have become attractive materials for fundamental research because of their structure, properties, and preparation [9–11]. Like Ag, Zn can also be used for photo-doping in chalcogenide glasses [12–17]. There are successful reports of doping of Zn Se x Te 1x in the literature that are suitable for the development of light emitting diodes. Keeping the above aspect in mind we have decided to study Zn based Se–Te alloys. In our earlier communication, we reported the measurements of thermally stimulated current (TSC) in a-Se 70 Te 28 Zn 2 and calculated the value of trap depth using these measurements. In the present paper, concentration of traps (N t ) and trap depth (E t ) have been calculated using the same measurements in Se 70 Te 30x Zn x (x ¼ 2, 4) thin films. These measurements are carried out at three different heating rates. It is observed that the amount of thermally stimulated current gradually increases and the temperature (T m ), at which maxima occurs, shifts to high temperatures with increasing heating rate (b). 2. Theory of measurements There are several methods in literature to evaluate the trapping parameters from experimental TSC curve such as curve fitting, heating rates, initial rise method. However, in this paper we chose the simplest case in which only one trap level is contributing to the TSC at a time which is known as single trap analysis. Although chalcogenide glasses may have trap distributed throughout the mobility gap, it appears justifiable to use the single trap analysis to calculate the trapping parameters in the present case, as pointed out by Simmons et al. [18,19]. We summarize the results for a single trap level, in the slow and fast re-trapping limit, and show how the trap parameters can be calculated in this case. Slow re-trapping means that the probability of recapture of thermally liberated carries by traps is much smaller than recombination, whereas in fast re-trapping the recombination probability is small as compared to the recapture [20]. Both the cases have been treated in literature and one finds that the TSC for a material with a single trap level in the fast as well as in slow re-trapping case is given by a general equation IðT Þ¼ A exp E t =kT  B=b Z T T 0 expðE t =kT Þ dT   (1) ARTICLE IN PRESS Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/physb Physica B 0921-4526/$ - see front matter & 2009 Published by Elsevier B.V. doi:10.1016/j.physb.2009.04.015 à Corresponding author. E-mail address: dr_ashok_kumar@yahoo.com (A. Kumar). Physica B 404 (2009) 2225–2228