Abstract Some sputtering processes of GaAs and Ti onto glass, c-Si and c-GaAs substrates have been carried out in order to obtain thin films as candidates to be intermediate band photovoltaic materials. This work presents first results concerning the optical and structural properties of the different deposited thin films. I. INTRODUCTION Nowadays, some compounds are under study as candidates to intermediate band photovoltaic materials. It has been shown that the introduction of states in a semiconductor band gap presents an alternative to multijunction solar cell designs for improving the power conversion efficiency [1],[2]. Most intermediate band material candidates are based on III- V semiconductors, GaP and GaAs, having transition metal atoms forming part of the structure composition [3]-[5]. Some of most interesting compound candidates could be Ti x Ga n As m compounds [6],[7]. One way to obtain these kinds of compounds is to use rf- sputtering deposition process. Sputtering processes allow depositing thin-films of GaAs and Ti having well controlled properties. In this work, we study the optical and structural properties of different thin films of GaAs-Ti and GaAs deposited by sputtering on glass, c-Si and c-GaAs substrates. II. SPUTTERING PROCESS DESCRIPTION Two different structures, obtained from two sputtering deposition processes carried out. The description of these processes is given below. A. Deposition of thin-film GaAs on glass, c-Si and c-GaAs substrates A first sputtering process was carried out, using a 4" GaAs target, in a RF Sputtering System : ESM100 Edwards & RFS5 Generator-300W. The GaAs target was undoped, had with (100) crystalline orientation, resistivity >= 10 7 ohm- cm, and a mobility>= 5000 cm 2 /V.sec. The process conditions were: 100W power and argon pressure of 5•10 -3 mbar. Thin thin-films 60nm thick were grown by sputtering on substrates of glass, c-Si and c-GaAs. B. Sputtering of GaAS and Ti on c-GaAs and c-Si substrates In order to study the incorporation of Ti atoms in the GaAs matrix, a second sputtering process was carried out using the above described 4" GaAs target, and a second Ti target in the same RF Sputtering System, using the same process conditions. In this run we used c-Si and c-GaAs substrates. The first steep was the deposition by sputtering of Ti films, with thicknesses in the range of 50nm, onto the substrates, and later a second GaAs, 50nm thick, over the Ti films. III. MAIN RESULTS OBTAINED The GaAs sputtering rates were in the range of 180-200 nm h -1 . Optical transmittance measurements on the GaAs thin films over glass, see Fig.1, allow the estimation of the optical gap. The obtained value of 1.5 eV, suggest that the deposited films present amorphous structure [8]. 300 400 500 600 700 800 900 1000 0,0 0,1 0,2 0,3 0,4 0,5 0,6 0,7 GaAs 60 nm on Glass P=100 W / Ar =5•10 -3 mbar Transmittance (%) Wavelenght (nm) Fig. 1. Optical Transmittance of GaAs sputtered samples on glass. This amorphous state was also confirmed by Photoreflectance measurements (PR). It has been reported that microcrystalline GaAs thin films with lower energy gap can be Analysis of GaAs-Ti thin films deposited by sputtering onto c-Si and GaAs S.Silvestre, Senior Member, IEEE, J. Puigdollers, A. Boronat, L.Castaæer, Senior Member, IEEE. Micro & Nano Technologies Group (MNT)- Departament D’Enginyeria Electrnica (DEE)- UPC Mdul C4, Campus Nord UPC, C/Jordi Girona 1-3, 08034 Barcelona, Spain Phone: 34-93-4017491; fax: 34-93-4016756; e-mail: santi@ eel.upc.edu 5 978-1-4244-2839-7/09/$25.00 (∃)2009 ∗&&& 1ΣΠcΦΦΕϑΟΗΤ ΠΓ ΥΙΦ 2009 4ΘΒΟϑΤΙ ∃ΠΟΓΦΣΦΟcΦ ΠΟ &ΜΦcΥΣΠΟ %ΦvϑcΦΤ - ∋ΦΧ 11-13, 2009. 4ΒΟΥϑΒΗΠ ΕΦ ∃ΠΝΘΠΤΥΦΜΒ, 4ΘΒϑΟ. Authorized licensed use limited to: UNIVERSITAT POLITÈCNICA DE CATALUNYA. Downloaded on March 12,2010 at 10:31:26 EST from IEEE Xplore. Restrictions apply.