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Device development for doping evaluation in nanowires using capacitance-voltage measurements

Nylander, Emil LU (2016) PHYM01 20161
Solid State Physics
Department of Physics
Abstract
This thesis aims to show the prospect of capacitance measurements over nanowire arrays as an evaluation method of the p-doping level in weakly p-doped p-n nanowires. The premise of the method is that there will be a high yield of statistical data regarding the doping level of the nanowires. The majority of the work carried out and presented in this thesis is however aimed at the manufacturing of a device suitable for said evaluation, and thus a range of different properties for materials were investigated. Due to early signs of parallel resistance in the device, allowing for an undesirably high back current, the disassociating isolator material as well as radial overgrowth of n-type InP was questioned. The isolating resist Cyclotene... (More)
This thesis aims to show the prospect of capacitance measurements over nanowire arrays as an evaluation method of the p-doping level in weakly p-doped p-n nanowires. The premise of the method is that there will be a high yield of statistical data regarding the doping level of the nanowires. The majority of the work carried out and presented in this thesis is however aimed at the manufacturing of a device suitable for said evaluation, and thus a range of different properties for materials were investigated. Due to early signs of parallel resistance in the device, allowing for an undesirably high back current, the disassociating isolator material as well as radial overgrowth of n-type InP was questioned. The isolating resist Cyclotene 3044-46 was thoroughly investigated before it was discarded due to its lacking electrical properties. The optional combination of SiO2 and photoresist S1818 was instead favored, albeit the resulting prolonged processing times. A device was created through various epitaxial, lithographic and etching techniques, creating a device inspired by the design used in nanowire-based solar cells. The design still needs further improvement, in order to eliminate flaws influencing the current through the device. Since the usage of Cyclotene would simplify the design and decrease the manufacturing time, further investigation into the origins of the poor electrical properties is of great interest. (Less)
Popular Abstract
As the world becomes more and more integrated with modern technology it becomes more reliant on an ever evolving market, and the demand for new technology pushes for innovative new solutions. The field of nanowires has shown to be interesting for e.g. the computer as well as the optical luminescence industry. Nanowires are much like a 'normal' wire structures confined by a small width in comparison to its length and can for example have a width of 200 nm and a length of 2 µm. The small dimensions of nanowires opens up for new interesting opportunities. However, these kind of new systems require new methods to be developed in order to fully understand them. One such struggle is that of determining impurities in p-type doped nanowires. With... (More)
As the world becomes more and more integrated with modern technology it becomes more reliant on an ever evolving market, and the demand for new technology pushes for innovative new solutions. The field of nanowires has shown to be interesting for e.g. the computer as well as the optical luminescence industry. Nanowires are much like a 'normal' wire structures confined by a small width in comparison to its length and can for example have a width of 200 nm and a length of 2 µm. The small dimensions of nanowires opens up for new interesting opportunities. However, these kind of new systems require new methods to be developed in order to fully understand them. One such struggle is that of determining impurities in p-type doped nanowires. With better understanding of the material nanowires could e.g. replace traditional transistors in computers.

Many methods used for systems with larger dimensions have well understood physics behind them. One of these methods uses capacitance in order to determine any small concentrations of different materials inside the nanowires. If shown applicable for smaller dimensions too it could be a great tool for better understanding these kinds of systems. Attempts at exploring the prospect of this method have previously been carried out, but problems with obtaining a suitable setup that would allow for the kind of measurements required were encountered. However, as a working method would prove very useful the project was revitalized.

A system was designed that would allow for the kind of capacitance measurements desired. Previous devices had had a problem with unwanted current paths. As the newly designed device solved this problem the small concentration of different materials in the so-called p-doped region of an InP nanowire could be evaluated. The calculated doping level in the weakly p-doped region was found to be in the order of 10^19 cm^-3, a concentration that would be called 'high'.

Even though the attempts yielded questionable results there were still signs that the method could be utilized if the mathematical model used to analyze the data obtained from the measurements was improved. During measurements on samples with different material concentration levels indications that it would be possible to distinguish between concentration levels were found. If the method is further pursued it might prove fruitful, becoming a standardized method used by the semiconductor community. (Less)
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author
Nylander, Emil LU
supervisor
organization
course
PHYM01 20161
year
type
H2 - Master's Degree (Two Years)
subject
language
English
id
8891548
date added to LUP
2016-09-13 11:14:50
date last changed
2016-11-15 13:31:08
@misc{8891548,
  abstract     = {This thesis aims to show the prospect of capacitance measurements over nanowire arrays as an evaluation method of the p-doping level in weakly p-doped p-n nanowires. The premise of the method is that there will be a high yield of statistical data regarding the doping level of the nanowires. The majority of the work carried out and presented in this thesis is however aimed at the manufacturing of a device suitable for said evaluation, and thus a range of different properties for materials were investigated. Due to early signs of parallel resistance in the device, allowing for an undesirably high back current, the disassociating isolator material as well as radial overgrowth of n-type InP was questioned. The isolating resist Cyclotene 3044-46 was thoroughly investigated before it was discarded due to its lacking electrical properties. The optional combination of SiO2 and photoresist S1818 was instead favored, albeit the resulting prolonged processing times. A device was created through various epitaxial, lithographic and etching techniques, creating a device inspired by the design used in nanowire-based solar cells. The design still needs further improvement, in order to eliminate flaws influencing the current through the device. Since the usage of Cyclotene would simplify the design and decrease the manufacturing time, further investigation into the origins of the poor electrical properties is of great interest.},
  author       = {Nylander, Emil},
  language     = {eng},
  note         = {Student Paper},
  title        = {Device development for doping evaluation in nanowires using capacitance-voltage measurements},
  year         = {2016},
}