Journal of Crystal Growth 198/199 (1999) 316—320 Formation of polycrystalline thin films of CuInS  by a two step process R.W. Miles*, K.T. Ramakrishna Reddy, I. Forbes Newcastle Photovoltaics Applications Centre, School of Engineering, University of Northumbria, Ellison Place, Newcastle upon Tyne NE1 8ST, UK Abstract CuInS  thin films have been prepared using a two-step process. This involved the deposition of approximately 1700 alternate layers of Cu and In onto molydenum coated glass substrates using magnetron sputtering followed by an anneal in an environment containing elemental sulphur to synthesise the compound. This process results in a Cu  In  precursor phase free from inhomogeneous secondary phases and the synthesis of the compound using elemental sulphur. This method results in densely packed, randomly orientated polycrystalline layers with the chalcopyrite crystal structure with as-synthesised grain sizes greater than 0.75 m for 1 m thick layers. Optical data obtained for these layers indicate a direct energy band gap of 1.45 eV. This is the first time that CuInS  layers have been produced by suphurising magnetron sputtered multiple Cu—In multilayers using elemental sulphur.  1999 Elsevier Science B.V. All rights reserved. Keywords: CuIns  thin films; Magnetron sputtering 1. Introduction The I—III—VI  chalcopyrite structure compounds and related alloys are currently of interest for use as light absorbing layers in thin film solar cells. This interest arises because out of the many highly ab- sorbing semiconductor compounds available the grain boundaries and other crystal imperfections in * Corresponding author. Tel.: # 44 191 2274595; fax: # 44 191 2273650; e-mail: robert.miles@unn.ac.uk.  Permanent address: Department of Physics, Sri Venkates- wara University Tirupati-517 502, India. polycrystalline layers of these materials do not ap- pear to be severely detrimental to device perfor- mance, and unlike devices made using most other thin film materials, devices made using I—III—VI  compounds are found to be stable. The most exten- sively studied I—III—VI  compound is CuInSe  which in polycrystalline form has resulted in devi- ces with efficiencies close to 17% [1]. To minimise reductions in efficiency of these devices with modest increases of temperature (due to the narrow energy band gap of CuInSe  , 0.95—1.0 eV), and to increase the open circuit voltage of devices, more complex alloys e.g. CuGaInSe  are currently being investi- gated to widen the energy band gap, [1]. A related 0022-0248/99/$ — see front matter  1999 Elsevier Science B.V. All rights reserved. PII: S 0 0 2 2 - 0 2 4 8 ( 9 8 ) 0 1 0 3 6 - 7