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Title: Transport simulations of ZnO nanowires and semiconductor devices in the presence of scanning probes
Author: Kryvchenkova, Olga
ISNI:       0000 0004 5370 3287
Awarding Body: Swansea University
Current Institution: Swansea University
Date of Award: 2015
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A simulation methodology to model contact and non-contact microscopy measurements has been developed within a 3-D finite element commercial device simulator by Silvaco. The tip-sample system is modelled self-consistently including tip-induced band bending and realistic tip shapes. When modelling scanning tunnelling microscopy, the resulting spectra from III-V semiconductors show good agreement with experimental results and a model based on the Bardeen tunnelling approach. We have found that the image force induced barrier lowering increases the tunnelling current by three orders of magnitude when tunnelling in to the sample valence band, and by six orders of magnitude when tunnelling in to the sample conduction band. We have shown that other models which use a single weighting factor to account for image force in the conduction and valence bands are likely to underestimate the valence band current by three orders of magnitude. The role of probe shank oxide formed at the tip in air has been examined by carrying out contact and non-contact current-voltage simulations of GaAs when the probe oxide has been controllably reduced. For both contact and non-contact simulations, the contact resistance change due to oxide is dependent on polarity and as confirmed experimentally. An electrostatic tip apex interaction with an In203 thin film transistor under operation is studied using a combination of experimental electrostatic force microscopy measurements and simulations. An error in the surface potential near the drain electrode is observed in simulations due to the tip induced band bending. Two point probe measurements on ZnO nanowires and 3-D transport simulations reveal the change in the electrical behaviour of nanoscale contacts from Schottky-like to Ohmic-like when the size of Au catalyst particles is changed at the ends of free-standing ZnO nanowires in relation to the nanowire cross-section. In addition, a geometry dependent current crowding effect was analysed in the combination with self-heating calculations. Finally, we have investigated carrier confinement at the ZnO/GaZnO interface due to band offset and polarization effects. We have found that this material system is a good candidate for polarization heterostructure field effect transistors.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Nanowires ; Semiconductors