Trialkylammonium salts of [M(SC{O}R)4]– (M = Ga3+ and In3+) as precursors for metal sulfide thin films

Abstract

A series of trialkylammonium salts of indium and gallium thiocarboxylates, [Et3NH][M(SC{O}Ph)4]·H2O (M = In3+ (1), Ga3+ (2)) and [n-Bu3NH][In(SC{O}Ph)4] (3), [R3NH][In(SC{O}Me)4] (R = Et (4) and n-Bu (5)) have been synthesized and characterized. The structure of 2 has been determined by single crystal X-ray diffraction and was found to be isomorphous and isostructural with [Et3NH][In(SC{O}Ph)4]·H2O (1) reported earlier. Thermal properties of 1–5 were studied. Compound 4 exhibits a phase transition which was characterized by DSC. Thermogravimetric and pyrolysis experiments of 1, 3, 4 and 5 showed the formation of tetragonal β-In2S3 while 2 yielded poorly crystalline monoclinic Ga2S3. Thin films of tetragonal In2S3 were obtained on a Ni coated Si substrate by MOCVD experiments using 1. Under similar conditions, 2 resulted in a film containing both cubic γ-Ga2S3 and hexagonal Ni0.96S. When a Cu coated Si substrate was used 1 deposited thin films of tetragonal CuInS2, while 2 furnished a mixture of tetragonal Cu1.96S and tetragonal CuGaS2 films. The composition of the thin films also depends on the temperature employed during the growth process. The composition, stoichiometry, phase analysis and surface morphology of the thin films obtained have been unequivocally characterized using XRD, SEM, TEM, RBS, Selective Area Electron Diffraction and XPS. It appears that the decomposed product(s) of 1 and 2 react with the substrate to form the metal sulfide thin films.