Dissertation / PhD Thesis

FZJ-2017-02932

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Ladungstransportmessung an GaAs-Nanodrähten und Entwicklung eines Tieftemperatur-Vierspitzen-RastertunnelmikroskopsCharge transport measurements at GaAs-nanowires and development of a low-temperature four-tip scanning tunneling microscope-3

Junker, H. H. R. (Corresponding author)

2016
RWTH Aachen University Aachen

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Please use a persistent id in citations: http://hdl.handle.net/2128/14172  urn:nbn:de:hbz:82-rwth-2016-119506  doi:10.18154/RWTH-2016-11950

Abstract: In order to perform charge transport measurements on freestanding as-grown GaAs nanowires, a room-temperature multi-tip scanning tunneling microscope was utilized as a nanoprober. Four-point resistance measurements along individual nanowires were performed with high spatial resolution. Subsequently, three different samples, grown with different temperature patterns, were investigated. Detailed resistance profiles along several nanowires on each sample were recorded. Three different regions were identified in the resistance profiles: A high resistance region at the nanowire bases (resulting from a suppressed dopant incorporation), a transition region in the middle with higher resistance and a low resistance region at the nanowire tops, with a desired amount of dopant incorporation.A calculation of the size of the depleted zone revealed that nanowires were completely depleted in the high resistance segments. Only in the low resistance region, the current could ow through the conduction channel in the nanowire core. In the high resistance region, the current was owing through surface states. In the transition region, the measured four-point IVs showed a non-linear characteristic. At high biases, the current could transfer from the surface to the better conducting core, while for low biases, the current had to ow via the surface. During the resistance profling, electron beam induced currents were present in the transition region as well as around the nanowire base on the substrate. A new customized low-temperature ultra-high vacuum four-tip scanning tunneling microscope capable of charge and magneto transport measurements has been realized to carry out charge transport measurements on semiconductor nanowires at liquid helium temperature. In order to navigate the four STM tips to desired positions, an SEM was used. SEM images of a test sample were used to optimize the vibration isolation of the experiment. A new nanopositioner (KoalaDrive) was developed to approach the tips to the sample. It could be shown that the KoalaDrive is capable of performing at low temperature (5 K), in ultra-high vacuum with high precision. In images taken with this STM, atomic steps on graphite as well as the 525 reconstruction of the Pt(100) surface could be resolved. The low-temperature multi-tip scanning tunneling microscope was used to contact single as-grown GaAs nanowires with one tip. Charging of a part of the tip holders prevented SEM images and conduction measurements with more tips.

Note: RWTH Aachen University, Diss., 2016

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Contributing Institute(s):

1. Funktionale Nanostrukturen an Oberflächen (PGI-3)

Research Program(s):

1. 141 - Controlling Electron Charge-Based Phenomena (POF3-141) (POF3-141)

Appears in the scientific report 2017

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