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Infuence of surface and crystal structure on the conductivity of individual InAs and InP nanowires

Kral, Lena Isabel Tamara LU (2015) In Bachelor thesis FYSK01 20151
Synchrotron Radiation Research
Department of Physics
Abstract
To satisfy the great need for (opto-)electronic devices to become smaller and more efficient in energy and price, research is done on semiconducting III-V nanowires (NWs). Electrical devices using NWs show noteworthy assets being fast-paced with high-speed electronics and low power consumption, one of which are high-efficient solar cells at a moderate price.

Developing electric devices it turns out to be of importance to measure individual NW conductivities for further improvements, if possible even in their upright standing growth geometry. Even though in the past this shaped up to be difficult, a new method was executed: utilizing scanning tunneling microscopy and a top contact method individual NWs are localized and contacted to... (More)
To satisfy the great need for (opto-)electronic devices to become smaller and more efficient in energy and price, research is done on semiconducting III-V nanowires (NWs). Electrical devices using NWs show noteworthy assets being fast-paced with high-speed electronics and low power consumption, one of which are high-efficient solar cells at a moderate price.

Developing electric devices it turns out to be of importance to measure individual NW conductivities for further improvements, if possible even in their upright standing growth geometry. Even though in the past this shaped up to be difficult, a new method was executed: utilizing scanning tunneling microscopy and a top contact method individual NWs are localized and contacted to finally be able to measure their individual conductance behavior.

This new method was employed in this thesis by investigating two NW systems that are promising for application in high-speed electronics and energy harvesting. First the influence of boundary interfaces between wurtzite and zinc blende structures on the conductivity of InAs NWs was investigated. It is shown that these transitions play an important role in combination with the existence of oxides on the surface. Cleaning the NWs with hydrogen results in an unexpected consequence: The current rises significantly with almost two orders of magnitude, going hand in hand with a much larger conductivity. In addition one can observe the current-voltage behavior to become more homogeneous.

Secondly, the influence of a passivation layer coating photovoltaic InP NWs is investigated. Determining an ideality factor of n = 2,4 ± 0,2 confirms the improvement of conductivity caused by the passivation layer. Lastly and contrary to expectations no photovoltaic response of the InP NW sample could be observed which is further discussed. (Less)
Popular Abstract
Solar cells play with no doubt an important role in the production of sustainable energy. Contributing to their efficiency in both, cost and energy gain is the goal of this project. To succeed we had to dare to leave the trodden path trying out new methods.

One big problem in the solar industry is the very low efficiency of affordable solar cells, using only about 5% of the solar energy. This is now countered making use of tiny standing wires, called nanowires, instead of continuous bulk material.

These nanowires are very small, having a diameter of about 100 nm which equals one thousandth of the width of a regular human hair. Their length is with several µm comparatively large. Imagining these tiny wires as minimized hairs, one can... (More)
Solar cells play with no doubt an important role in the production of sustainable energy. Contributing to their efficiency in both, cost and energy gain is the goal of this project. To succeed we had to dare to leave the trodden path trying out new methods.

One big problem in the solar industry is the very low efficiency of affordable solar cells, using only about 5% of the solar energy. This is now countered making use of tiny standing wires, called nanowires, instead of continuous bulk material.

These nanowires are very small, having a diameter of about 100 nm which equals one thousandth of the width of a regular human hair. Their length is with several µm comparatively large. Imagining these tiny wires as minimized hairs, one can easily understand what is special about nanowires: Because of their big surface compared to their volume, entirely new material properties can arise.

Implementing nanowires in solar cells cause much smaller material consumption and therefore significantly reduces the production cost. To make this work in an efficient way, the aim of this project is to analyze the nanowires which are used in single processing steps on the way of fabricating a complete solar cell. Only in understanding these individual steps can we adequately optimize the whole system. In the process we measure the properties of single nanowires (with the help of a scanning tunneling microscope) instead of taking an average of millions of wires in a finished solar cell, how it is conventionally done. This type of conductivity measurements is quite unique, only done by a few research teams in the world.

But our research does not stop here. Additionally we are investigating properties of the lattice structure of nanowires, more specifically what structures favor or constrain the conductance of nanowires. These nanowires can then be implemented not only in solar cells, but also in various electrical devices like LEDs, transistors and sensors. (Less)
Please use this url to cite or link to this publication:
author
Kral, Lena Isabel Tamara LU
supervisor
organization
course
FYSK01 20151
year
type
M2 - Bachelor Degree
subject
keywords
semiconducting nanowire, zinc blende, wutzite, hydrogen cleaning, STM, oxidation, photovoltaic response, photovoltaics, top contact method, InAs, nanowire, InP
publication/series
Bachelor thesis
language
English
id
5431103
date added to LUP
2015-06-02 09:18:08
date last changed
2015-06-02 09:30:25
@misc{5431103,
  abstract     = {To satisfy the great need for (opto-)electronic devices to become smaller and more efficient in energy and price, research is done on semiconducting III-V nanowires (NWs). Electrical devices using NWs show noteworthy assets being fast-paced with high-speed electronics and low power consumption, one of which are high-efficient solar cells at a moderate price. 

Developing electric devices it turns out to be of importance to measure individual NW conductivities for further improvements, if possible even in their upright standing growth geometry. Even though in the past this shaped up to be difficult, a new method was executed: utilizing scanning tunneling microscopy and a top contact method individual NWs are localized and contacted to finally be able to measure their individual conductance behavior.

This new method was employed in this thesis by investigating two NW systems that are promising for application in high-speed electronics and energy harvesting. First the influence of boundary interfaces between wurtzite and zinc blende structures on the conductivity of InAs NWs was investigated. It is shown that these transitions play an important role in combination with the existence of oxides on the surface. Cleaning the NWs with hydrogen results in an unexpected consequence: The current rises significantly with almost two orders of magnitude, going hand in hand with a much larger conductivity. In addition one can observe the current-voltage behavior to become more homogeneous.

Secondly, the influence of a passivation layer coating photovoltaic InP NWs is investigated. Determining an ideality factor of n = 2,4 ± 0,2 confirms the improvement of conductivity caused by the passivation layer. Lastly and contrary to expectations no photovoltaic response of the InP NW sample could be observed which is further discussed.},
  author       = {Kral, Lena Isabel Tamara},
  keyword      = {semiconducting nanowire,zinc blende,wutzite,hydrogen cleaning,STM,oxidation,photovoltaic response,photovoltaics,top contact method,InAs,nanowire,InP},
  language     = {eng},
  note         = {Student Paper},
  series       = {Bachelor thesis},
  title        = {Infuence of surface and crystal structure on the conductivity of individual InAs and InP nanowires},
  year         = {2015},
}