Fabrication and Characterization of Single GaAs Nanowire Devices
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In this work, a reproducible fabrication process for contacting single GaAs nanowires (NWs) using electron beam lithography (EBL) has been established. Wurtzite (WZ) GaAs core NWs doped with Te and Be have then been investigated along with intrinsic NWs using photocurrent spectroscopy techniques. It is found that shifts of the fabricated metal contacts are minimized by consistent use of alignment positions and that thick resist introduces contrast issues for small alignment features during EBL. Thick resist further introduces metal shadowing effects during metal deposition. Different surface treatments for removing contaminants and native oxide from the NW surface have been tested to obtain ohmic contacts to the GaAs NWs.Photocurrent wavelength (WL) dependence measurements on intrinsic core NWs show a sharp change near the zink blende (ZB) GaAs band gap, and no free exciton peak is observed at low temperatures. ZB stacking faults in the NWs are believed to cause shifts from the real WZ band gap. Doped core NWs show an intrinsic-like I-V and WL dependence behavior, indicating that dopants are not electrically active. This observation, and the absence of a free exciton peak, is attributed to the high surface state density of GaAs. I-V characterization on intrinsic and doped NWs shows that ohmic contact is not achieved using the tested surface treatments. Preliminary studies on etching AlGaAs shells of GaAs/AlGaAs core-shell NWs show that 50:1 citric acid/hydrogen peroxide solution is a good etchant candidate for future studies using AlGaAs passivated intrinsic and doped GaAs NWs.