TY  - THES
A3  - Pietsch, Ullrich
AB  - The pnCCD detector became an instrument which shows wide applications in material research. Besides white-beam Laue diffraction von single and polychrystalline materials the multilayer analysis of hard coatings and soft matter we demonstrate first application for the analysis of semiconductor nanowires (NWs). 
For the first time, a frame-store pn-junction CCD has been applied for structure analysis of semiconductor nanowires by means of energy-dispersive Laue diffraction using white synchrotron radiation in the energy range of 8 to 120 keV. Here a white x-ray beam exposes the sample providing a number of Laue spots which fulfill the Bragg condition for different x-ray energies. The fast and precise characterization of any materials by this method requires a simultaneous position and energy resolved detection of X-rays.
The aim of this project was to investigate the real structure of different semiconductor NWs using white beam and pn CCD detector. Firstly, we present  X-ray diffraction pattern taken from a periodic GaAs NW array that was grown onto GaAs[111]B surface. The experiment was performed at the home laboratory at Siegen University using a coplanar Bragg reflection. The structural properties were probed by measuring reciprocal space by quasi single shot exposure. Besides the peak related to the reflection from GaAs substrate, we found a second peak referring to the reflection from NWs.  Form the difference of peak positions and peak energies the lattice mismatch between the NWs and the substrate was deduced.
Secondly, a more detailed analysis was performed on InAs NWs grown onto GaAs[111]B. The experiment was carried out at the EDR beam line of BESSY II synchrotron. Energy-dispersive X-ray diffraction techniques rely on a high usable photon flux in a wide energy range (5< E< 35 KeV) so that as many Bragg peaks as possible can be detected in a single X-ray shot without any sample rotation. In addition, the usage of high-energy X-ray diffraction enables to measure a large section of reciprocal space at the same time allowing for probe the real structure of the InAs NWs and substrate GaAs and insensitive reflections simultaneously. By this experiment we could deduce the simultaneous appearance of wurtzite and zinc-blende phases in InAs NWs.
Finally, we measured GaAs/InxGa1-x As/GaAs core-shell NWs grown by molecular beam epitaxy (MBE) onto a Si (111) substrate at the EDDI beamline of BESSY II. In this system, the incident x-ray beam energy ranges between 20 to 120 keV and illuminates the sample nearly parallel to the [111] direction. Due to the wide range of x-ray energies provided various Laue spots of few highly indexed {hkl} families with different lattice plane fulfill the Bragg condition simultaneous. After the evaluation the Laue spots and correction caused by the small misalignment of the incident beam with respect to [111] direction the pseudomorphic growth of the InxGa1-x As shell and the GaAs core has been verified.
In summary, by using white synchrotron radiation the pnCCD provides a three dimensional intensity distribution composed by two pixel coordinates and an energy direction covering a 3D data volume in reciprocal space. In this sense, the system provides a good possibility to investigate the structure of semiconductor NWs (GaAs, InAs, GaAs/ InxGa1-x As /GaAs) because several Laue reflections can be probed simultaneous which is impossible using monochromatic radiation.
AU  - Algashi, Alaa
DA  - 2019
DO  - 10.25819/ubsi/640
KW  - CCD-Sensor
KW  - Nanowires
KW  - pn-CCD detector
KW  - Synchrotron radiation
LA  - eng
PY  - 2019
TI  - Application of pn-CCD detector for imaging of nanowires using white synchrotron radiation
UR  - https://nbn-resolving.org/urn:nbn:de:hbz:467-15446
Y2  - 2024-11-24T01:27:20
ER  -