0000000000389782
AUTHOR
Heruy Taddese Mengistu
Spontaneous core–shell elemental distribution in In-rich In(x)Ga1-xN nanowires grown by molecular beam epitaxy.
International audience; The elemental distribution of self-organized In-rich InxGa1-xN nanowires grown by plasma-assisted molecular beam epitaxy has been investigated using three different techniques with spatial resolution on the nanoscale. Two-dimensional images and elemental profiles of single nanowires obtained by x-ray fluorescence and energy-dispersive x-ray spectroscopy, respectively, have revealed a radial gradient in the alloy composition of each individual nanowire. The spectral selectivity of resonant Raman scattering has been used to enhance the signal from very small volumes with different elemental composition within single nanowires. The combination of the three techniques ha…
Simulations of Piezoelectric, Electronic and Optical Properties of Nanowires
Los nanohilos semiconductores han atraido un interés creciente debido a sus potenciales aplicaciones en electrónica, óptica y fotónica. Un amplio rango de dispositivos fotónicos y electrónicos basados en nanohilos han sido ya demostrados, incluyendo células solares, fotodetectores, diodos emisores de luz, y láseres. Para comprender las propiedades de los nanohilos es necesario conocer su estructura electrónica. Además, es importante conocer cómo estas propiedades dependen del tamaño, estructura cristalina y orientación, y cómo se ven afectadas por las deformaciones. El objetivo de esta tesis es desarrollar modelos teóricos realistas, pero manejables desde un punto de vista computacional, pa…
Elemental distribution and structural characterization of GaN/InGaN core-shell single nanowires by Hard X-ray synchrotron nanoprobes
Improvements in the spatial resolution of synchrotron-based X-ray probes have reached the nano-scale and they, nowadays, constitute a powerful platform for the study of semiconductor nanostructures and nanodevices that provides high sensitivity without destroying the material. Three complementary hard X-ray synchrotron techniques at the nanoscale have been applied to the study of individual nanowires (NWs) containing non-polar GaN/InGaN multi-quantum-wells. The trace elemental sensitivity of X-ray fluorescence allows one to determine the In concentration of the quantum wells and their inhomogeneities along the NW. It is also possible to rule out any contamination from the gold nanoparticle …
The generalized plane piezoelectric problem: Theoretical formulation and application to heterostructure nanowires
We present a systematic methodology for the reformulation of a broad class of three-dimensional (3D) piezoelectric problems into a two-dimensional (2D) mathematical form. The sole underlying hypothesis is that the system geometry and material properties as well as the applied loads (forces and charges) and boundary conditions are translationally invariant along some direction. This class of problems is commonly denoted here as the generalized plane piezoelectric (GPP) problem. The first advantage of the generalized plane problems is that they are more manageable from both analytical and computational points of view. Moreover, they are flexible enough to accommodate any geometric cross secti…
Electronic and optical properties of InN nanowires
Abstract We have employed a multiband envelope function method to study wurtzite [0001] InN nanowires of cylindrical cross section. The electronic subband structure and optical absorption spectrum are calculated as a function of the nanowire radius. The energies of the Γ -point conduction band states show a monotonous increase with decreasing radius. On the other hand, the size dispersion of the valence band states is more involved, showing various crossing and anticrossing effects due to the interplay between the confinement and band mixing effects. Thus, for small ( R 2 nm ) nanowires the highest valence band state has dominant p z -symmetry, but for R > 2 nm the highest state has dominan…