Contribution study of properties of copper indium diselenide thin films S. Mehdaoui a, * , O. Aissaoui a , N. Benslim a , M. Benabdesslem a , L. Bechiri a , L. Mahdjoubi a , G. Nouet b,1 a Laboratoire d’Etudes des Surfaces et Interfaces de la Matie`re Solide (LESIMS), De´partement de physique, Universite´ Badji Mokhtar, Annaba, BP.12, 23200, Annaba, Alge´rie b ENSI-CAEN/SIFCAM-UMR-CNRS 6176, 6-Boulevard du Mare ´chal-Juin, 14032 Cedex, France article info Article history: Received 12 December 2006 Received in revised form 18 December 2007 Accepted 24 December 2007 Keywords: Ternary semiconductors Chalcopyrite Thin films Activation energies Defects abstract Stoichiometric powder of CuInSe 2 (CIS) was prepared from molten stoichiometric quantities of the el- ements. The structure analyzed by X-ray diffraction powder (XRD), shows mainly the chalcopyrite phase. CIS polycrystalline thin films deposited from this powder have been grown on glass substrates in vacuum by thermal evaporation method. The structural and electrical properties of both as-deposited and an- nealed films were studied using X-ray diffraction and dark conductivity measurements respectively. As- prepared films at room temperature showed an amorphous structure. However, the chalcopyrite structure with (112) preferential orientation was observed after annealing in vacuum at 400  C during 30 min. The influence of the annealing process on the dark conductivity of the films was also discussed. Ó 2008 Elsevier Ltd. All rights reserved. 1. Introduction Polycrystalline Cu-III-VI 2 thin films have become in the last few decades a suitable alternative as photovoltaic absorbers for highly efficient and low-cost solar cells [1–3]. These materials and their quaternary alloys cover an energy band gap range of 0.8–2.5 eV [4– 6]. Among these materials, copper indium diselenide (CuInSe 2 ) is one of the most promising candidates for the production of low- cost photovoltaic devices. The extraordinarily high absorption co- efficient of this material (>10 5 cm 1 ) makes thin film solar cells practical, even though the optical band gap (1.04 eV) is low for optimum conversion efficiency [7]. It can be prepared with n- as well as with p-type conductivity and therefore both homojunction and heterojunction potential exists for this material [8]. Recently, a remarkable high cell efficiency of 18.8% was reported [9]. The physical properties of CuInSe 2 (CIS) thin films prepared by different techniques are extensively studied by various authors. Y.D. Tembhurkar et al. [10] have deposited CuInSe 2 thin films by spray pyrolysis and studied their structural, optical and electrical prop- erties. They conclude that p-type CuInSe 2 polycrystalline films with chalcopyrite structure and two direct allowed transitions at 0.93 and 1.26 eV can be obtained. They also found that the grain boundary effect was present at low temperatures. A.A.S. Akl et al. [11] have studied the structural properties of flash evaporated CuInSe 2 thin films at different preparation parameters (substrate temperature and post annealing period). They found that the preparation conditions greatly affect crystallinity of the films. S.M. Firoz Hasan et al. [12] have shown that electrical conductivity is largely dependent on Cu/In percentage ratio for sequentially de- posited CuInSe 2 films. Our contribution study on this subject has been focused on preparation and investigation of the structural and electrical properties of the CuInSe 2 thin films prepared by thermal evaporation method. 2. Experimental details 2.1. Thin film preparation CuInSe 2 thin films (0.9–1.5 mm) were thermally evaporated from tungsten crucible on corning glass substrates. The fine-grained powder of CuInSe 2 which was used as an evaporant was obtained by melt-growth method. More details of this process are published elsewhere [13]. The samples were deposited at non-heated sub- strates. Afterwards these specimens were annealed in evacuated quartz tube (10 2 Torr) using an electrical furnace at different temperatures (100–400  C) during 30 min. In order to avoid the re-evaporation of Se (melting point ¼ 217  C), the annealing tem- perature and dwell time were carefully chosen. For electrical measurements, two metal electrodes layers of Cr and Ag were successively deposited on glass substrates before depositing of the thin film in a coplanar geometry. The first layer of chromium was evaporated to improve the adhesion of the CIS with the glass substrates and the second layer of the silver (Ag) was used for the electrical contact (better conductor). * Corresponding author. E-mail address: fac782004@yahoo.fr (S. Mehdaoui). 1 Tel.: þ33 (0) 2 13 45 26 54; fax: þ33 (0) 2 31 45 26 60. Contents lists available at ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum Vacuum 82 (2008) 1194–1197 Contents lists available at ScienceDirect Vacuum journal homepage: www.elsevier.com/locate/vacuum 0042-207X/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.vacuum.2007.12.017