New Molecular Precursors for Metal Sulfides

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Abstract

Metal sulfide thin films are important class of materials which have applications in photovoltaics, microelectronics and displays. Chemical vapour deposition (CVD) is well known method for the deposition of high quality thin films. Very few classes of single source precursors (eg: dithiocarbamates, xanthates) were successful for the deposition of good quality metal sulfide films by MOCVD. This limited choice was due to the difficulties of finding precursors with suitable physico-chemical properties. Hence, it is important to develop precursors with suitable volatility, solubility and being able to deposit films with little or no contamination. This work describes the synthesis of a series of metal (Fe, Co, Ni, Zn, Cd) complexes of thio- and dithio-biuret ligands, their structural and spectroscopic characterization and thermal decomposition. The complexes were used as single source precursors for the deposition of iron, cobalt, nickel, zinc, cadmium and zinc cadmium sulfide thin films by AACVD. The effect of alkyl groups, coordinating atoms, deposition temperatures on phases and morphology of the films were studied. The deposited films were characterised by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), selected area electron diffraction (SAED), and atomic force microscopy (AFM). The complex [Fe(SON(CNiPr2)2)3] gave hexagonal troilite FeS films with small amount of tetragonal pyrrhotites Fe1-xS at 300 °C, whereas only troilite FeS was deposited at 350, 400 or 450 °C. Complexes [Fe2(µ-OMe)2 (SON(CNEt2)2)2] and [Fe(SON(CNEt2)2)3] deposited a mixture of hexagonal troilite FeS and cubic pyrite FeS2 films at all temperatures. [Fe(SON(CNMe2)2)3] deposited very thin films of FeS at all temperatures as troilite. Complexes [Co(N(SCNMe2)2)3] and [Co(N(SCNEt2)2)3] deposited hexagonal Co1-xS films at all temperatures of 350-500 °C, whereas [Co(SON(CNiPr2)2)2] gave mixture of cubic and hexagonal Co4S3 films at 280-400 °C. Thiobiuret complex [Ni(SON(CNMe2)2)2] gave orthorhombic Ni7S6. Complexes [Ni(SON(CNMe2CNEt2))2] and [Ni(SON(CNEt2)2)2] gave mixtures of hexagonal Ni17S18 and orthorhombic Ni7S6. In contrast, [Ni(SON(CNiPr2)2)2] gave orthorhombic Ni9S8. Dithiobiuret complexes [Ni(N(SCNMe2SCNEt2))2] and [Ni(N(SCNEt2)2)2] gave hexagonal NiS1.03 at 360 and 400 °C, orthorhombic Ni7S6 phase at 440 and 480 °C. The zinc complexes [Zn(N(SCNMe2)2)2] and [Zn(SON(CNiPr2)2)2] deposited cubic ZnS at 300 and 350 °C, whereas at 400 and 450 °C hexagonal ZnS were apparent [Zn(N(SCNEt2)2)2] gave hexagonal ZnS films at all deposition temperatures. Cadmium complexes [Cd(N(SCNMe2)2)2], [Cd(N(SCNEt2)2)2] and [Cd(SON(CNiPr2)2)2] gave hexagonal CdS films at all deposition temperatures.

Keyword(s)

Chemical Vapor Deposition; Metal Sulfide, ; Precursors Development

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