Moldavian Journal of the Physical Sciences, Vol.3, N 3-4, 2004 299 POINT GROUP DETERMINATION OF A CuIn 4 Se 6 SINGLE CRYSTAL M. León a , R. FernАndez - Ruiz b , V. Tezlevan c , E. Arushanov c a- Universidad Autónoma de Madrid, Departamento Física Aplicada C-XII, 28049 Madrid, Spain. maximo.leon@uam.es ; Fax: 34913973969 (corresponding author) b- Universidad Autónoma de Madrid, S.I.d.I. C-IX, 28049 Madrid, Spain c- Institute of Applied Physics, Academy of Sciences of Moldova, Kishinev, MD 2028, Moldova Single crystals of CuIn 4 Se 6 were grown. Tilting the sample, several Laue patterns were undertaken. These diagrams showed high mono-crystallinity and lamellar habit normal to c axis. Analysing the properties of the several Point Groups (P.G.) compatible with the Lauegrams and studying the optical activity of samples, the hexagonal ⎯62m (3/m2) P.G. remains as the only one compatible with the experiments. 1. Introduction CuInSe 2 and related chalcopyrite-type semiconductors are leading candidates for absorbers in high-efficiency photovoltaic devices. It is now believed that CuIn 3 Se 5 or similar Cu poor compounds, as CuIn 5 Se 8 or CuIn 2 Se 3.5 , tend to segregate in all Indium-rich CuInSe 2 films, i.e. all films yielding high efficiency solar cell [1]. The CuIn 3 Se 5 layer is expected to play an important role in the high efficiency CuInSe 2 solar cells [1-4]. In spite of the importance of CuIn 3 Se 5 in technological applications and in the understanding of the basic physics, so far the characteristics of CuIn 3 Se 5 or similar Cu poor compound single crystals have not been yet reported. As mentioned by Tiwari et al. [5,6] and confirmed by Marin et al. [7], it is still difficult to grow single crystals of CuIn 3 Se 5 . Different attempts like the solid state growth method, the travelling heater method, vertical Bridgman with and without previous synthesis, selenization of stoichiometric Cu and In in liquid phase by evaporating Se at different temperatures and programmed directional freezing techniques [4,7] were made to prepare bulk crystals. However, the reported attempts were not successful to grow CuIn 3 Se 5 single crystals [1-15]. On the other hand, the crystal structure analysis of synthesised CuIn 3 Se 5 , CuIn 5 Se 8 and CuIn 2 Se 3.5 give rise to discrepancies. Hanada et al. [12,13] have proposed a structure model for CuIn 3 Se 5 based on a stannite type structure with S.G. I 4 2m. A structural characterisation of bulk β-Cu 0.39 In 1.20 Se 2 (β-CuIn 3.08 Se 5.13 ) performed by Hönle et al. [14] and more recently by Marín et al.[7] indicates that this phase exhibits a tetragonal structure with S.G. P 4 2c named by the authors P-chalcopyrite. Regarding that both S.G. I 4 2m and P 4 2c are not subgroups of I 4 2d, which is the S.G. of CuInSe 2 , CuIn 3 Se 5 is not related to the chalcopyrite type structure. It is neither a vacancy ordered compound nor a defect chalcopyrite structure. Recently, the group of T. Wada [15] has grown hexagonal and tetragonal CuIn 5 Se 8 thin films, showing that only the hexagonal phase is stable. The group of M. León [4,16] has synthesized polycrystalline Cu 2 In 4 Se 7 , CuIn 3 Se 5 and CuIn 5 Se 8 in vacuum under different cooling conditions resulting in different phases. X-ray diffraction and Rietveld refinement of the diagrams were used to characterize the different structures obtained. The two former compounds were refined in S.G. P 4 2c. On the other hand, for the CuIn 5 Se 8 compound a far