Fabrication and Characterization of Single Doped GaAs Nanowire Devices
In the work with this master thesis, electron beam lithography (EBL) and other clean
room methods was used to develop a reproducible process for making ohmic contacts
to nanowires (NWs), with the aim of investigating different dopants influence on
their physical properties. After optimizing the EBL process, good alignment of the
contact patterns to the NWs was achieved by doing a thorough alignment procedure.
A detailed write field alignment close to the sample position prior to the 3-point alignment, along with consistent use of alignment positions, was found the be especially important to reduce misalignment.
For surface treatment it is shown how a diluted HCl solution is used to remove
native oxide on the NW surface, and how a solution of citric acid and hydrogen peroxide
can be used to effectively etch the AlGaAs shell of core-shell nanowires, though
selective etching of AlGaAs on GaAs is difficult. Further, an ammonium sulphide
solution is used to passivate the surface prior to metal deposition.
Metalization was done using an electron beam evaporator, however optimal thin
films could not be achieved due to the presence of strain. This is believed to originate in the evaporation of electron beam resist (ER) during metal deposition due to high local heating of the samples. While this was remedied by, among other, depositing thinner films at high deposition rates, it could not be fully avoided. Nevertheless, satisfactory lift-off was still achieved in most cases.
IV characterization of the different samples was done using a probing station. The
samples generally display asymmetric and non-linear characteristics, indicating that
ohmic contacts have not been achieved. Annealing tests was also done on a number
of samples, and while this generally resulted in more linear IV curves, the current
was also reduced in most cases.
Place, publisher, year, edition, pages
Institutt for elektronikk og telekommunikasjon , 2011. , 61 p.
ntnudaim:6334, MTEL elektronikk, Nanoelektronikk og mikrosystemer
IdentifiersURN: urn:nbn:no:ntnu:diva-14043Local ID: ntnudaim:6334OAI: oai:DiVA.org:ntnu-14043DiVA: diva2:445813
Weman, Helge, Professor