This letter shows that selective heteroepitaxy of nanometer-scale InAs whiskers on SiO2-patterned GaAs substrates [Yazawa, Koguchi, and Hiruma, Appl. Phys. Lett. 58, 1080 (1991)] is induced by surface contamination with Au resulting from the fluorocarbon plasma etching process used to etch the SiO2 mask. We demonstrate that high densities (≂1010/cm2) of InAs nanowhiskers 20–30 nm in diameter can be epitaxially grown on InAs(111)B substrates onto which 1 monolayer of Au atoms had been deposited. This wirelike growth appears to be induced by ultrafine alloy droplets generated by the reactions between Au-clusters and InAs substrates.
Self‐assembled nanostructures based on indium arsenide whiskers grown using molecular beam epitaxy and metal‐organic vapor phase epitaxy (see Figure) could be of use as lead wires, connecting devices in integrated nanodevices. The procedure employed to produce these features in a controlled way is described, and the possibilities of developing nanowhisker heterojunctions discussed.
The effects of post-deposition annealing on the microstructure of tantalum oxide ( Ta2O5) deposited on Si are evaluated by means of X-ray photoelectron spectroscopy. With the peak decomposition technique and the angle-resolved X-ray photoelectron spectroscopy (ARXPS) method we found that there is SiO2 layer and Ta suboxide at the interface. By using a simple two-layer model, the thickness of both the Ta2O5 layer and the interfacial SiO2 layer could be evaluated. Investigating Ta2O5 films this way before and after annealing revealed that annealing has the following effects on the interfacial reaction. With post-deposition annealing under O2, Ar, or N2 gas, the Si substrate is oxidized by oxygen from the Ta2O5 layer. The Ta2O5 is partly reduced and N2 gas activates this reaction. The thickness of the interfacial SiO2 layer is reduced by nitridation of the Si substrate.
The thickness and composition of ultrathin silicon nitride films which are deposited on Si substrates and on thin thermal oxide are estimated by means of X-ray photoelectron spectroscopy (XPS). With use of the peak decomposition technique and angle-resolved XPS (ARXPS), the distribution of the silicon nitride and oxide in the films is determined. Both the nitride and oxide thicknesses are evaluated. The thickness determined by XPS agrees with the thickness determined by cross-sectional transmission electron microscopy (TEM). This XPS method is valid for estimation of the thickness and composition of ultrathin silicon nitride films, and it has the advantages of accuracy over ellipsometry and convenience over TEM.
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