Control of the morphologies or profiles produced by localized etching of
normalGaAs
structures has assumed increasing importance with the current emphasis being placed on microdefinition and surface relief optimization for
normalGaAs
monolithic circuits. To obtain a better understanding of the complex anisotropic etching behavior observed in
normalGaAs
, the morphologies produced by various acidic hydrogen peroxide solutions were evaluated. The degree and nature of the anisotropy is shown to vary extensively and systematically with the etchant composition. Both highly anisotropic and essentially isotropic etching may be obtained by selection of the appropriate etchant composition.
Gallium arsenide deposition rate studies were conducted with an open tube, chloride transport system which permitted independent control of the reactant input partial pressures. A recording microbalance was adapted to the deposition apparatus so that the epitaxial growth rates could be continuously measured during the actual deposition process. At low temperatures and high reactant partial pressures the process appears to be kinetically controlled. The rate then becomes inversely proportional to the gallium monochloride partial pressure and may indicate the presence of a competitive adsorption process. At high temperatures and low partial pressures the rates may be described in terms of a “quasi‐equilibrium” model where a fraction of the incoming gas stream equilibrates with the condensed phase.
Epitaxial deposition of gallium arsenide in holes etched into gallium arsenide substrates was investigated. Single crystal deposits with excellent surfaces were obtained. The effect of substrate orientation on the degree of lateral overgrowth above the substrate surface was studied. Depositions in {100} oriented substrates produce faceted deposits, whose upper surfaces are several microns above the substrate surface. Epitaxial hole deposits with surfaces level with or nearly level with the substrate surface are obtained with accurately oriented {111}‐B substrates.
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