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Scanning Probe Microscopy on Semiconductor Nanowires for Photovoltaics

Sedlak, Steffen Matthias LU (2013) FYSK01 20131
Department of Physics
Synchrotron Radiation Research
Abstract
The purpose of this thesis is to examine nanowires made up of compound III-V-semiconductors which can be applied as photovoltaic devices. Two types of experiments are done approaching from two different starting points: Firstly, studies of several III-V-semiconductor wafer surfaces used as a reference for studies of nanowire surfaces and secondly, direct contacting of standing nanowires in order to determine the characteristic variables of the wires. The focus is put on the behaviour of a single nanowire aiming to draw a comparison with the properties measured for nanowires applied in a nanowire array solar cell which have been studied before. The two approaches will finally help to differentiate between actual wire properties and other... (More)
The purpose of this thesis is to examine nanowires made up of compound III-V-semiconductors which can be applied as photovoltaic devices. Two types of experiments are done approaching from two different starting points: Firstly, studies of several III-V-semiconductor wafer surfaces used as a reference for studies of nanowire surfaces and secondly, direct contacting of standing nanowires in order to determine the characteristic variables of the wires. The focus is put on the behaviour of a single nanowire aiming to draw a comparison with the properties measured for nanowires applied in a nanowire array solar cell which have been studied before. The two approaches will finally help to differentiate between actual wire properties and other factors that might have influence on the measurements.
The experimental methods are various manners of scanning probe microscopy. For the surface studies conventional scanning tunnelling microscopy is performed. The experiments involving upright standing nanowires are done by from-top-contacting with the tungsten tip of a scanning tunnelling microscope.
The measurements accomplished within ten weeks are adequate for drawing conclusions. Many images of clean indium arsenide and gallium antimonide surfaces are obtained. Specifically the InAs(110)-, the InAs(111)A-, the InAs(111)B- and the GaSb(100)-surface are examined. By from-top-contacting ten indium phosphide nanowires grown as pin-diodes are analysed.
The results of both surface studies and contacting are satisfying: On three surfaces atomic resolution is reached and reconstructions can be proven. All four show individuated characteristics which can be compared with each other. For the indium phosphide diodes a photoresponse of single wires are observed. Various aspects are taken into account, such as angle or temperature dependence. The ideality factor, the short-circuit-current and the open-circuit-voltage is determined for most of the wires.
The proposals which this thesis suggests regarding further research are to repeat the contacting within vacuum, where the wires can be kept clean from oxides. As the contact for every nanowire is established in the same way independent from cleaning comparisons with measurements performed on horizontally lying lithographically contacted nanowires will be interesting. Employing a tuneable light source the efficiency of a single standing nanowire could furthermore be determined and compared with the nanowire array solar cell. For the surface studies the cleaning parameters for the GaSb(100)-surface should be determined in detail. (Less)
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author
Sedlak, Steffen Matthias LU
supervisor
organization
course
FYSK01 20131
year
type
M2 - Bachelor Degree
subject
keywords
nanowires, photovoltaics, surface reconstruction, scanning tunneling microscopy, III-V-semiconductor, semiconductor, surface science, p-n-junction, solar energy
language
English
id
3633829
date added to LUP
2013-04-18 23:17:45
date last changed
2013-04-18 23:17:45
@misc{3633829,
  abstract     = {The purpose of this thesis is to examine nanowires made up of compound III-V-semiconductors which can be applied as photovoltaic devices. Two types of experiments are done approaching from two different starting points: Firstly, studies of several III-V-semiconductor wafer surfaces used as a reference for studies of nanowire surfaces and secondly, direct contacting of standing nanowires in order to determine the characteristic variables of the wires. The focus is put on the behaviour of a single nanowire aiming to draw a comparison with the properties measured for nanowires applied in a nanowire array solar cell which have been studied before. The two approaches will finally help to differentiate between actual wire properties and other factors that might have influence on the measurements.
The experimental methods are various manners of scanning probe microscopy. For the surface studies conventional scanning tunnelling microscopy is performed. The experiments involving upright standing nanowires are done by from-top-contacting with the tungsten tip of a scanning tunnelling microscope.
The measurements accomplished within ten weeks are adequate for drawing conclusions. Many images of clean indium arsenide and gallium antimonide surfaces are obtained. Specifically the InAs(110)-, the InAs(111)A-, the InAs(111)B- and the GaSb(100)-surface are examined. By from-top-contacting ten indium phosphide nanowires grown as pin-diodes are analysed.
The results of both surface studies and contacting are satisfying: On three surfaces atomic resolution is reached and reconstructions can be proven. All four show individuated characteristics which can be compared with each other. For the indium phosphide diodes a photoresponse of single wires are observed. Various aspects are taken into account, such as angle or temperature dependence. The ideality factor, the short-circuit-current and the open-circuit-voltage is determined for most of the wires.
The proposals which this thesis suggests regarding further research are to repeat the contacting within vacuum, where the wires can be kept clean from oxides. As the contact for every nanowire is established in the same way independent from cleaning comparisons with measurements performed on horizontally lying lithographically contacted nanowires will be interesting. Employing a tuneable light source the efficiency of a single standing nanowire could furthermore be determined and compared with the nanowire array solar cell. For the surface studies the cleaning parameters for the GaSb(100)-surface should be determined in detail.},
  author       = {Sedlak, Steffen Matthias},
  keyword      = {nanowires,photovoltaics,surface reconstruction,scanning tunneling microscopy,III-V-semiconductor,semiconductor,surface science,p-n-junction,solar energy},
  language     = {eng},
  note         = {Student Paper},
  title        = {Scanning Probe Microscopy on Semiconductor Nanowires for Photovoltaics},
  year         = {2013},
}