AVS 61st International Symposium & Exhibition
    Nanometer-scale Science and Technology Tuesday Sessions
       Session NS+AS+SS-TuA

Paper NS+AS+SS-TuA4
Scanning Tunneling Microscopy of Semiconductor Nanowire Surfaces and Devices

Tuesday, November 11, 2014, 3:20 pm, Room 304

Session: Nanowires and Nanotubes: Advances in Growth and Characterization 
Presenter: Anders Mikkelsen, Lund University, Sweden
Authors: R. Timm, Lund University, Sweden
J. Knutsson, Lund University, Sweden
M. Hjort, Lund University, Sweden
S. McKibbin, Lund University, Sweden
O. Persson, Lund University, Sweden
J.L. Webb, Lund University, Sweden
A. Mikkelsen, Lund University, Sweden
Correspondent: Click to Email
III-V semiconductor nanowires (NWs) offer tremendous possibilities for device application in solid-state lightning, energy conversion, and information technology [1]. With their small diameter and their very large surface-to-volume ratio, the NW device behavior is strongly determined by their surface structure. Thus, it is both essential and challenging to investigate their atomic surface structure and to combine this information with electrical measurements on individual NWs.

Recently, we have managed to clean InAs NWs from their native oxide and revealed the atomic arrangement of their side surfaces with scanning tunneling microscopy (STM). Here, we present STM images of various NW surfaces of both wurtzite and zincblende crystal structure [2], including InAs, GaAs, InP, and InSb NWs. By combining STM imaging with scanning tunneling spectroscopy (STS) measurements, we simultaneously study the surface structure and local electronic properties across the interfaces of NW heterostructures [3].

For correlating local structural and electronic characterization with transport measurements of NW devices, we have developed a novel STM-based setup: We are using combined atomic force microscopy (AFM) and STM/S on individually contacted NWs for mapping the surface structure and the local band alignment along the NW heterostructure under device performance. We show initial results of this unique approach on InAs-GaSb nanowire tunnel diodes, where we could prove Esaki behavior of a NW while it was investigated by STM/AFM. From a set of STS spectra we determined the position of the Fermi level along the nanowire for different applied biases, showing an abrupt drop directly at the material interface. In a reverse experiment, we used the STM/AFM tip as local gate and measured the resulting source-drain current through the nanowire for different biases [4].

In some cases it is desirable to measure the conductivity of individual as-grown nanowires in an upright-standing configuration without any sample processing. Here we have developed an alternative setup where the STM tip is used to first image free-standing nanowires from top and then form a point contact [5]. We will demonstrate the reproducibility of this method in establishing low-resistive Ohmic contacts to individual InP and InAs nanowires [6], and we will show initial results on the I-V properties of individual InP NW solar cells.

[1] J. Wallentin et al., Science 339, 1057 (2013)

[2] M. Hjort et al., Nano Lett. 13, 4492 (2013)

[3] M. Hjort et al., ACS Nano 6, 9679 (2012)

[4] J. L. Webb et al., Nano Res., in print

[5] D. B. Suyatin et al., Nature Commun. 5, 3221 (2013)

[6] R. Timm et al., Nano Lett. 13, 5182 (2013)