Organometallic Precursors for III-V Semiconductors
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ORGANOMETALLIC PRECURSORS FOR rnI-V SEMICONDUCTORS ERIN K. BYRNE, TREVOR DOUGLAS, AND KLAUS H. THEOPOLD Department of Chemistry, Baker Laboratory, Cornell University, Ithaca, New York 14853 ABSTRACT Organometallic molecules containing covalently linked gallium and arsenic or indium and phosphorus have been synthesized and characterized spectroscopically and by X-ray diffraction. These precursors can be transformed into the corresponding III-V materials in a chemical reaction proceeding at ambient temperature. The compound semiconductors prepared in this way are obtained as amorphous powders. During the reaction, quantum size effects may be observed by UV-VIS spectroscopy as the particles grow. INTRODUCTION HI-V semiconductors (i.e. compounds consisting of an element from group III and one from group V in a 1:1 stoichiometry, e.g. gallium arsenide, indium phosphide etc.) are materials of great technological interest. The high electron mobility in GaAs as well as the band gaps of these compounds (in the visible and infrared light region) make them indispensable for the design of very fast integrated circuits and optoelectronic devices. The manufacture of these devices requires the deposition of very thin films used to form quantum wells or twodimensional electron gases, and the deposition of highly pure semiconductors on various substrates. Currently many device quality films are grown by "Organometallic Vapor Phase Epitaxy" (OMVPE), a process in which volatile molecules containing the desired elements are flowed over a heated substrate. The technology associated with carrying out these reactions in a controlled fashion has evolved to the point that films of near atomic thickness (-3 A) can be produced. Despite this apparent success several problems remain to be solved before the full potential of Ill-V semiconductors can be realized. Arsine (AsH 3 ) is one of the most toxic gases known (inhalation of as little as 0.5 ppm may be dangerous), making its large scale use in plants unattractive. The nonstoichiometric nature of the gas mixtures is responsible for deviations from
the desired 1: 1 ratio of group M element and group V element in the solid, thus introducing antisite defects (e.g. As occupying Ga sites) into the semiconductor film. The reactant chemistry usually governs the range of acceptable deposition temperatures and some heterostructures can not be formed in this range of temperatures, as they are destroyed by thermal diffusion. Finally, and probably most serious of all, the OMVPE process in its current form does not lend itself to commercialization of devices based on III-V semiconductors because of the complexity of apparatus which is required to achieve dimensional control and uniformity of the semiconductor films. The solutions to these problems lie in the design of novel and more sophisticated precursors for the preparation of HI-V semiconductors. Some time ago we began work involving the synthesis of III-V molecules and a study of their reactivity. It is our belief that investigations of the reactio
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