L Journal of Alloys and Compounds 325 (2001) 12–17 www.elsevier.com / locate / jallcom Characterization of Cu Ag InSe thin films 0.5 0.5 2 * G. Venkata Rao, G. Hema Chandra, O.M. Hussain, S. Uthanna, B. Srinivasulu Naidu Thin Film Laboratory, Department of Physics, Sri Venkateswara University, Tirupati — 517 502, India Received 1 December 2000; accepted 7 March 2001 Abstract Cu Ag InSe thin films prepared by the flash evaporation technique onto Corning 7059 glass substrates at T 5683–703 K were 0.5 0.5 2 S single phase, nearly stoichiometric and polycrystalline with a strong (112) preferred orientation. The electrical resistivity of the films was in the range 30–300 V cm. Thermoelectric power and Hall effect measurements indicated p-type conduction in the films. The temperature dependence of the electrical conductivity suggested that above 455 K the conduction mechanism was intrinsic, whereas extrinsic / impurity conduction dominated in the range 303–433 K.  2001 Elsevier Science B.V. All rights reserved. Keywords: Thin films; Semiconductors; Electrical transport; Thermoelectric 1. Introduction an attempt has been made to study the composition, structure, electrical conductivity, Hall mobility and ther- Recently there has been a great deal of interest in the moelectric power of Cu Ag InSe thin films. 0.5 0.5 2 study of ternary and quaternary chalcopyrite compounds. Among these, CuInSe and AgInSe have proved to be 2 2 stable and efficient absorber materials for fabricating 2. Experimental polycrystalline thin film heterojunction solar cells [1–5] and also find application in electronic devices [6–7]. These Ingots of Cu Ag InSe have been prepared using 0.5 0.5 2 ternary chalcopyrite compounds are direct band gap semi- constituent elements of 99.999% pure copper, silver, conductors showing a threefold optical structure [8] near indium and selenium (obtained from M/S Johnson Matth- the fundamental edge due to crystal–field and spin–orbit ey, UK) weighed in stoichiometric ratio. The mixture was splitting of the upper most valence band. Studies on sealed in a quartz ampoule under a pressure of less than 25 Cu Ag InSe thin films as absorber material are still 10 Torr. The sealed ampoule was placed in a vertical x 12x 2 more attractive, since they allow tailoring of the optical furnace and the temperature was slowly increased at the 21 band gap and other properties. By gradually substituting rate of 30 K h up to 473 K. The ampoule was copper by silver, the optical band gap can be increased maintained at that temperature for a period of 24 h to from 1.04 to 1.24 eV.Very little work has been reported on minimize pressure build-up and to avoid possible strong bulk Cu Ag InSe [9–14]. Gremenok et al. [15] re- exothermic reactions. The temperature was then increased x 12x 2 21 ported the growth and characterization of Cu Ag InSe at the rate of 60 K h up to 973 K, beyond which a slow x 12x 2 ( x50, 0.3, 0.5, 0.7 and 1.0) thin films prepared by pulsed heating process was used to minimize the risk of cracking. laser deposition. The films prepared at T 5723–753 K The ampoule was kept at 1373 K for a period of 48 h. The S were single phase, polycrystalline and stoichiometric with- quartz ampoule was rotated intermittently for 2–3 h to in 4% and they observed a nonlinear composition depen- ensure complete mixing and reaction of the constituents. It dence of the optical energy gap. A better understanding of was then cooled slowly to room temperature. In order to the structural, electrical and optical properties is essential ensure better homogeneity, the mixture was heated two for optimizing these films for solar cell fabrication. Hence, times and each time it was kept at 1373 K for 12 h and slowly cooled to room temperature. The compound was then ground and reduced to 200–300 mesh powders. *Corresponding author. E-mail address: bsrinivasulunaidu@usa.net (B. Srinivasulu Naidu). Cu Ag InSe thin films were prepared by the flash 0.5 0.5 2 0925-8388 / 01 / $ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0925-8388(01)01395-0