Single Source Precursors for the Growth of Metal-Chalcogenide Thin Films
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Single Source Precursors for the Growth of Metal-Chalcogenide Thin Films Allen L. Seligson*, Philip J. Bonasia*, John Arnold*, Kin-Man Yu*, Jim M. Walker', and Edith D. Bourret't * Departmentof Chemistry, University of California,Berkeley CA 94720
MaterialsSciences Division, Lawrence Berkeley Laboratory. Berkeley CA 94720 f To whom correspondenceshould be adressed ABSTRACT We have recently reported the growth of ZnTe and CdTe thin films from the novel volatile single-source precursors Zn(sitel) 2 and Cd(sitel)2 [sitel = -TeSi(SiMe 3 ) 3]. In an effort to understand the role played by the bulky substituents, we have prepared a number of related compounds and have investigated their potential for the growth of I-VI materials. We now describe the synthesis and characterization of M[EX(SiMe 3 ) 3] 2 (M = Zn, Cd, Hg for E = Te, X = C; M = Zn for E = Se, X = C, Si) and their use as precursors molecules for the growth of ZnSe, ZnTe, CdTe and HgTe. The thin films were characterized by Rutherford Back scattering spectrometry (RBS) and X-ray diffraction. Pyrolysis reaction conditions for the alkyl and silyl chalcogenolates are also compared. INTRODUCTION The increasing number of applications for II-VI materials has expanded interest in methods for growth of epitaxial thin films. Organometallic vapor phase epitaxy (OMVPE) is a proven technique in this research. Precursors for OMVPE are limited to dual source compounds, where in each element is contained in a separate organometallic compound. More recently single molecule precursors have been developed that contain both II-VI elements covalently bound.1 These precursors have several advantages over dual source methods including lower toxicity, a simplified decomposition pathway and the potential for precise control over growth rates and stoichiometry. The problem facing most single molecule precursors reported to date is their low volatility. Successful growth of ZnS, CdS, CdZnS, and ZnSe films has been reported 2 using compounds incorporating bulky-ortho substituted arylchalcogenolate ligands. Although phenyl tellurolate complexes of group 12 metals are known to decompose to metal tellurides, 3 -5 their inherent lack of volatility precludes their use in film growth. We recently described the preparation of group 12 complexes incorporating the very bulky sitel ligand [sitel = -TeSi(SiMe3)3]. 6 These compounds are volatile as a result of their low molecularity, and we have previously shown that the zinc and cadmium 7 complexes are single-molecule precursors to ZnTe and CdTe thin films. Here we introduce some new sterically hindered ligands, "ctel" [ctel = TeC(SiMe 3 ) 3], "csel" [csel = -SeC(SiMe3)3] and "sisel" [sisel = -SeSi(SiMe3)31 that provide us with a range of substituted single-molecule precursors for growth of a variety of II-VI thin films. EXPERIMENTAL Our standard operating procedures were as described in preceding papers. 6 ,7 The complexes M(sitel)2 (M = Zn, Cd, Hg), HTeC(SiMe 3 ) 3 , HSeC(SiMe 3 ) 3 and 6 HSeSi(SiMe 3) 3 were prepared by literature methods. ,8 Sy
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