Transmission Electron Microscopy of Nanowires: Influence of Doping and Etching on Polytypism in InP
Abstract: Semiconductor nanowires have many properties which makes them interesting for future electronic devices. The fact that they have very small diameters allow them to combine different III-V materials into heterostructures, and makes it possible to grow them on Si substrates which are the basis of nearly all current semiconductor technology. It also allows them to adopt the wurtzite crystal structure in addition to the zincblende, which is the bulk form (except for III-nitrides). The small dimensions of the nanowires mean that there is a need for high resolution analysis of both crystal structure and composition locally. For this purpose transmission electron microscopy (TEM) is an excellent tool: crystal structure can be directly viewed using high resolution imaging and the electrons passing through the sample generate many signals, among them X-rays, which can be used for compositional analysis. In this thesis the effects of doping (with Zn and S) and etching (with HCl) on the nanowire crystal structure are analysed using high resolution TEM. These are procedures which will be essential in many device applications. To know the exact atomic arrangement at the interface between two crystal structures, higher resolution than is obtainable in conventional TEM is required. For this purpose a combination of hardware aberration corrected TEM and focal series reconstruction was used.
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