The Realization of Molecular Control Over Solid State Structure: Chemical Vapor Deposition of Gallium and Indium Sulfide
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THE REALIZATION OF MOLECULAR CONTROL OVER SOLID STATE STRUCTURE: CHEMICAL VAPOR DEPOSITION OF GALLIUM AND INDIUM SULFIDE FILMS MICHAEL B. POWER,a.b ANDREW N. MACINNES a~c ALOYSIUS F. HEPP,b
AND ANDREW R. BARRONa* a Department of Chemistry, Harvard University, Cambridge, MA 02138 b NASA, Lewis Research Center, Cleveland, OH 44135 c Gallia Inc., Weston, MA 02193 ABSTRACT The chemical vapor deposition of cubic gallium sulfide and tetragonal indium sulfide films is reported. The structure of the deposited films was demonstrated to be defined not solely by thermodynamics, but by the predesigned molecular motif of the precursor molecules. Analysis of the deposited films has been obtained by transmission electron microscopy (TEM), with associated energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). INTRODUCTION The low temperature deposition of thin-film materials from molecular precursors has been an area of increasing interest since the first studies by Manasevit over twenty years ago. 1,2 In principle, metal organic chemical vapor deposition (MOCVD) offers significant advantages over physical vapor deposition (PVD) methods; for example simple apparatus, mild process condition, control over composition, high deposition rates, and possible large scale processing. Perhaps the most significant advantage that CVD has over other methods is the production of metastable materials. Most CVD processes operate far from equilibrium conditions so that kinetically, rather than thermodynamically, favored products are produced. 3 However, an important question arises: Can the molecular structure of the precursor control the phase structure of a solid product? While several groups have shown that thermodynamically stable phases can be prepared by MOCVD from molecules designed to represent the smallest fragment of the solid state structure, none have demonstrated that new or high energy phases may be prepared by MOCVD from single molecular precursor. Research inour laboratory has, therefore, centered upon this goal and two recent results are discussed herein. EXPERIMENTAL The precursors [(tBu) 21n(StBu)12 and [(tBu)GaS] 4 were prepared according to our previously published procedures. 4 5, Chemical vapor depositions were carried out in an atmospheric pressure laminar-flow hot wall glass reactor, as previously described. 6 Argon as a carrier gas was passed through a Cr/Cr 20 3 gas purifier prior to entry into the chamber. Deposition was carried out on p-type (100) oriented silicon wafers and KBr crystals. The CVD system was loaded with * Author to whom all correspondence should be addressed. Mat. Res. Soc. Symp. Proc. Vol. 282. 01993 Materials Research Society
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substrates and purged for at least 2 hours prior to deposition during which time the hot zone was brought to the deposition temperature. Outflow from the reaction chamber exited to an oil bubbler, which prevented back flow of air into the reaction chamber. Once the chamber was brought to the desired temperature for deposition, approximately 500
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