Graduate Thesis Or Dissertation
 

GaAs(100) surface chemistry : interactions with molecular chlorine and sulfur compounds

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  • An important aspect in device technology is the processing of GaAs to produce highly-resolved etch patterns on the substrate. This is done typically on the GaAs(100) surface. Recently, a number of methods, all using chlorinated vapor reactants, have been applied to fabrication of GaAs devices. In spite of these technological advances, the understanding of the chemistry of the surface reaction on a fundamental level is still rudimentary. Practical etching involves a combination of chemical phenomenon and physical sputtering, in the presence of a mixture of chlorine containing gases to achieve material removal. The complexity of these processes precludes them as experiments for understanding the mechanisms responsible for etching. A simpler approach, used here, involves thermal etching and electron-induced desorption processes to study the material removed after a GaAs(100) surface is exposed to molecular chlorine. Another important aspect of device technology involves the atomic level interactions between metals and semiconductors as they are brought into contact. In this vein it has been found that sulfur containing compounds tend to lower the Schottky barrier height at the GaAs(100) surface, and thereby produce ohmic contacts at the metal-semiconductor interface. As with the GaAs/chlorine system, information on the GaAs/sulfur system is by no means conclusive. Molecular sulfur, hydrogen sulfide, as well as alkaline sulfides have all been used to deposit sulfur on the surface. This study concentrates on molecular sulfur and H₂S and the very different behavior between the two upon adsorption and subsequent desorption from the GaAs(100) surface. These experiments on clean, chlorine and sulfur covered surfaces were all performed on well characterized GaAs(100) substrates either cleaned in situ by ion bombardment and annealing (IBA) techniques or grown in situ by molecular beam epitaxy (MBE). The information was gathered using standard surface science techniques under ultra-high vacuum (UHV) conditions. These techniques allow investigation of structure, composition and reaction present at the surface of materials.
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