Non Linear Piezoelectricity in Wurtzite Semiconductor Core-Shell Nanowires: An Atomistic Modelling Approach

UoM administered thesis: Phd

  • Authors:
  • Hanan Alzahrani

Abstract

Piezotronics is a new field, as first explored by Professor Zhong Lin Wang (Georgia Institute of Technology, Atlanta, USA), which describes the exploitation of the piezoelectric polarization and internal electric field inside semiconductor nanostructures by applying strain, to develop electronic devices with new functionality. Such concepts find applications in both III-V and II-VI semiconductor compounds, in optics, optoelectronics, catalysis, and piezoelectricity, sensors, piezoelectric transducers, transparent conductor and nanogenerators. In this work I explore the strain dependence of the piezoelectric effect in wurtzite ZnO crystals. The Linear and quadratic piezoelectric coefficients of III-V (GaP, InP, GaAs and InAs) wurtzite semiconductors are also calculated using ab-initio density functional theory. The polarization in terms of the internal anion-cation displacement, the ionic and dipole charges is written and the ab initio Density Functional Theory is used to evaluate the dependence of all quantities on the strain tensor. The piezoelectric effect of III-V semiconductors are nonlinear in the strain tensor. The quadratic piezoelectric coefficients and a revised value of the spontaneous polarization are reported. Furthermore, the ZnO nanowires is found to be non-linear piezoelectric effect and leads to predictions in some cases opposite to those obtained using the widely used linear model. The predicted magnitude of such coefficients are much larger than previously reported and of the same order of magnitude as those of III-N semiconductors. We also model the bending distortion created on a III-V wurtzite nanowire by an atomic force microscope tip induced deflection to calculate the piezoelectric properties of both homogenous and core shell structures. A number of combinations of III-V materials for the core and the shell of the nanowires, are shown a favour much increased voltage generation. The largest core voltages in core/shell combinations of InAs/GaP, InP/GaP, GaP/ InAs and GaP/InP are observed which can be theoretically 3 orders of magnitude larger than the typical values of ±3V in homogenous nanowires. Also considering properties such as bandgap discontinuity and mobility, III-V wurtzite core shell nanowires are candidates for high performance components in piezotronics and nanogeneration.

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Original languageEnglish
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Award date1 Aug 2017