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Kryvchenkova O.,Multidisciplinary Nanotechnology Center | Kalna K.,Electronic Systems Design Center | Cobley R.J.,Multidisciplinary Nanotechnology Center
Conference Proceedings - 10th International Conference on Advanced Semiconductor Devices and Microsystems, ASDAM 2014 | Year: 2014

A full 3D model for the simulation of carrier transport, self-consistently coupled with thermal transport, has been developed for free-standing ZnO nanowires with Schottky contacts. The model predicts a complex distribution of the current density through the metal-semiconductor interface with a high current density area around the edge of the Schottky contact away from the contact centre. This high current density would result in increased Joule heating at the contact edge of the free standing ZnO nanowire leading to local temperature breakdown at the contact. Degradation with increasing temperature was also demonstrated. © 2014 IEEE. Source


Kryvchenkova O.,Multidisciplinary Nanotechnology Center | Cobley R.J.,Multidisciplinary Nanotechnology Center | Kalna K.,Electronic Systems Design Center
Applied Surface Science | Year: 2014

A simulation methodology to model tunnelling spectroscopy measurements based on the Price-Radcliffe formalism has been developed within a finite element device simulator. The tip-sample system is modelled self-consistently including tip-induced bending and realistic tip shapes. The resulting spectra of III-V semiconductors are compared against experimental results and a model based on the Bardeen tunnelling approach with very good agreement. We have found that the image force induced barrier lowering increases the tunnelling current by three orders of magnitude when tunnelling to the sample valence band, and by six orders of magnitude when tunnelling to the sample conduction band. The work shows that other models which use a single weighting factor to account for image force in the conduction and valence band are likely to be underestimating the valence band current by three orders of magnitude. © 2014 Elsevier B.V. All rights reserved. Source


Cobley R.J.,Multidisciplinary Nanotechnology Center | Rees P.,Multidisciplinary Nanotechnology Center | Teng K.S.,Multidisciplinary Nanotechnology Center | Wilks S.P.,Multidisciplinary Nanotechnology Center
Journal of Applied Physics | Year: 2010

Cross-sectional scanning tunneling microscopy (STM) has been used to study in-operation changes that occur at the active region of clean-cleaved semiconductor laser diodes. A tunneling model that allows the inclusion of tip-induced band bending and surface defect states has been used to study the origin of the surface changes which give rise to the observed modification. Low-doped layers close to the active region are found to undergo both a reduction in doping concentration and an increase in the surface defect state density as the lasers are operated. These changes ultimately lead to device failure. Under different tunneling modes STM can be sensitive to one effect or the other, and the importance of modeling the changes to confirm which are occurring is emphasized. © 2010 American Institute of Physics. Source


Cobley R.J.,Multidisciplinary Nanotechnology Center | Teng K.S.,Multidisciplinary Nanotechnology Center | Brown M.R.,Multidisciplinary Nanotechnology Center | Rees P.,Multidisciplinary Nanotechnology Center | Wilks S.P.,Multidisciplinary Nanotechnology Center
Applied Surface Science | Year: 2010

Cross-sectional scanning tunneling microscopy is used to study defects on the surface of semiconductor laser devices. Step defects across the active region caused by the cleave process are identified. Curved blocking layers used in buried heterostructure lasers are shown to induce strain in the layers above them. Devices are also studied whilst powered to look at how the devices change during operation, with a numerical model that confirms the observed behavior. Whilst powered, low-doped blocking layers adjacent to the active region are found to change in real time, with dopant diffusion and the formation of surface states. A tunneling model which allows the inclusion of surface states and tip-induced band bending is applied to analyze the effects on the tunneling current, confirming that the doping concentration is reducing and defect surface states are being formed. © 2010 Elsevier B.V. All rights reserved. Source

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