The chemical modification of n- and p-type hydrogen-passivated Si(100) surfaces by a scanning tunneling microscope (STM) is reported. The modified areas have been examined with STM, Auger electron spectroscopy, scanning electron microscopy, and atomic force microscopy. Comparison of these characterization techniques indicates the features are both chemical and topographic in nature and are the result of local oxidation of the substrate. In addition, pattern transfer for the defined regions has been demonstrated with both thermal oxidation and HBr reactive-ion etching.
The etching of GaAs and AlxGa1−xAs have been characterized in (NH4)2Sx solution with various excess sulfur concentrations and for temperatures ranging from 20 to 60 °C. The etch rate varies with the concentration of excess sulfur and is highest at 60 °C using a 4% excess sulfur solution. The etch rate of AlxGa1−xAs increases exponentially with increasing Al mole fraction. Activation energies of 19.8 and 15.9 kcal/mole are obtained for GaAs and Al0.3Ga0.7As in 4% (NH4)2Sx, respectively. These high values and the linear time dependence of etch rates signify that the etching process of AlxGa1−xAs in (NH4)2Sx solutions is predominantly reaction-rate limited. Possible chemical processes involved in the etching and the formation of a passivating sulfur layer are discussed.
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