Notes Synthesis of Gallium Chalcogenide Cubanes and Their Use as CVD Precursors for Ga 2 E 3 (E ) S, Se) Stephan Schulz,* ,1a Edward G. Gillan, 1b Jean L. Ross, 1a Lillian M. Rogers, 1c Robin D. Rogers,* ,1c and Andrew R. Barron* ,1b Departments of Chemistry, University of Iowa, Iowa City, Iowa 52242, The University of Alabama, Tuscaloosa, Alabama 35487, and Rice University, Houston, Texas 77005 Received June 14, 1996 X Summary: The gallium-chalcogen heterocubanes [Cp*Ga(µ 3 -E)] 4 ,E ) S(1) and Se (2), and [Cp † Ga(µ 3 - Se)] 4 (3) have been synthesized by dehalosilylation reactions between E(SiMe 3 ) 2 (E ) S, Se) and RGaCl 2 ,R ) Cp* (C 5 Me 5 ) and Cp † (C 5 Me 4 Et), and are characterized by elemental analyses, NMR spectroscopy, and mass spectrometry. The use of compounds 1 and 2 as single- source MOCVD precursors for the low-temperature growth of Ga 2 E 3 films at 290-310 °C is described. The as-deposited films were amorphous; however, upon thermal annealing (500 °C) the films crystallized to the thermodynamic cubic phases, while the corresponding tellurium analog decomposed in the solid state at 220 °C forming a gallium-rich product. Introduction Compounds containing group 13 and group 16 ele- ments are potential precursors for the corresponding 13-16 materials (III-VI materials) by metal organic chemical vapor decomposition (MOCVD). 2 Recently, thin films of materials, such as In x S y or Ga x S y , have been reported 3 to be suitable for the fabrication of optoelec- tronic devices, 4 as well as for passivation layers on GaAs and InP, 5 and dielectric layers in GaAs-based MISFET devices. 6 While the preparation of cyclic compounds of the type [R 2 M(µ-ER′)] n (M ) Al, Ga, In; E ) S, Se, Te; n ) 2, 3, 4) are well-known and have been described in numerous papers, 7 it is only recently that examples of cubane cage compounds, [(R)M(µ 3 -E)] 4 , have been reported. 8 Cu- banes can be synthesized either by reaction of MR 3 (M ) Al, Ga, In) with elemental S, Se, or Te 9,10 or by reaction of tetrameric monovalent group 13 compounds, [(R)M] 4 [M ) Al, R ) Cp*; M ) In, R ) C(Me 3 Si) 3 ] with the elemental chalcogens. 11 Unfortunately, both reac- tion types are limited to a few group 13 starting compounds. One attractive feature of cubanes as single-source precursors for CVD reactions are their clean decomposi- tion pathways. 12 Unlike compounds of the type [R 2 M- (µ-ER′)] n , cubanes do not possess strong E-C bonds which are potentially a source for carbon contamination of the resulting thin film material. In addition, we have shown recently the possibility of controlling the solid- state material’s crystal structure by using a predesigned molecular motif. 3b Our research has focused on devel- oping simple synthetic pathways to group 13-16 cu- banes and studying their decomposition reactions. Our particular interest is to find cubanes with a lower decomposition temperature than those of [( t Bu)Ga(µ 3 - S)] 4 , which decompose at 350 -400 °C, enabling gallium sulfide films to be deposited on a wider variety of thermally sensitive substrates. 13 Results and Discussion The reaction of Cp*GaCl 2 and Cp † GaCl 2 with E(SiMe 3 ) 2 (E ) S, Se), in toluene, leads to the new gallium chalcogen cubanes [Cp*Ga(µ 3 -S)] 4 (1), [Cp*Ga- * Authors to whom correspondence should be addressed. X Abstract published in Advance ACS Abstracts, October 1, 1996. (1) (a) University of Iowa. (b) Rice University. (c) University of Alabama. (2) For a review, see: Barron, A. R. Adv. Mater. Optics Electron. 1995, 5, 245. (3) See for example: (a) MacInnes, A. N.; Power, M. B.; Barron, A. R. Chem. Mater. 1992, 4, 11. (b) MacInnes, A. N.; Power, M. B.; Barron, A. R. Chem. Mater. 1993, 5, 1344. (c) Cheon, J.; Arnold, J.; Yu, K.-M.; Bourret, E. D. Chem. Mater. 1995, 7, 2274. (4) See for example: (a) Sze, S. M. Semiconductor Devices, Physics and Technology; John Wiley and Sons: Chichester, U.K., 1985. (b) MacInnes, A. N.; Cleaver, W. M.; Barron, A. R.; Power, M. B.; Hepp, A. F. Adv. Mater. Opt. Electron. 1992, 1, 229. (c) Ando, K.; Katsui, A. Thin Sold Films 1981, 76, 141. (5) See for example: (a) MacInnes, A. N.; Power, M. B.; Barron, A. R.; Jenkins, P. P.; Hepp, A. F. Appl. Phys. Lett. 1993, 62, 711. (b) MacInnes, A. N.; Power, M. B.; Barron, A. R.; Jenkins, P. P.; Hepp, A. F. Mater. Res. Soc., Symp. Proc. 1993, 282, 111. (c) Tabib-Azar, M.; Kang, S.; MacInnes, A. N.; Power, M. B.; Jenkins, P. P.; Hepp, A. F.; Barron, A. R. Appl. Phys. Lett. 1993, 63, 625. (6) Jenkins, P. P.; MacInnes, A. N.; Tabib-Azar, M.; Barron, A. R. Science 1994, 263, 1751. (7) For leading references, see for example: (a) Oliver, J. P.; Kumar, R.; Taghiof, M. In Coordination Chemistry of Aluminum; Robinson, G. H., Ed.; VCH: New York, 1993; p 167. (b) Rahbarnoohi, H.; Kumar, R.; Heeg, M. J.; Oliver, J. P. Organometallics 1995, 14, 3869. (c) Haggata, S. W.; Azad Malik, M.; Motevalli, M.; O’Brien, P. Chem. Mater. 1995, 7, 716. (d) Taghiof, M.; Heeg, M. J.; Bailey, M.; Dick, D. G.; Kumar, R.; Hendershot, D. G.; Rahbarnoohi, H.; Oliver, J. P. Organometallics 1995, 14, 2903. (8) For recent review articles, see: (a) Barron, A. R. Chem. Soc. Rev. 1993, 93. (b) Barron, A. R. Comm. Inorg. Chem. 1993, 14, 123. (9) Power, M. B.; Ziller, J. W.; Tyler, A. N.; Barron, A. R. Organo- metallics 1992, 11, 1055. (10) Harlan, C. J.; Gillan, E. G.; Bott, S. G.; Barron, A. R. Organo- metallics, in press. (11) (a) Schulz, S.; Roesky, H. W.; Koch, H. J.; Sheldrick, G. M.; Stalke, D.; Kuhn, A. Angew. Chem., Int. Ed. Engl. 1993, 32, 1729. (b) Uhl, W.; Graupner, R.; Layh, M.; Schu ¨ tz, U. J. Organomet. Chem. 1995, 93, C1. (12) Cleaver, W. M.; Spa ¨ th, M.; Hoyk, D.; McMurdo, G.; Power, M. B.; Stuke, M.; Rankin, D. W. H.; Barron, A. R. Organometallics 1995, 14, 690. (13) Our initial efforts in this area have involved the photoassisted MOCVD of GaS thin films; see: Pernot P.; Barron, A. R. Chem. Vap. Deposition 1995, 1, 75. 4880 Organometallics 1996, 15, 4880-4883 S0276-7333(96)00480-3 CCC: $12.00 © 1996 American Chemical Society