Optical Characterization of Single GaAs/AlGaAs Nanowires with
Combined Photoluminescence Spectroscopy and Transmission Electron
Microscopy on the Same Nanowire
L. Ahtapodov, J. Todorovic, P. Olk, T.S. Mjaaland, P.R.T. Slaattnes, D.L. Dheeraj,
A.T.J. van Helvoort, B.O. Fimland and H. Weman
The vast possibilities of combined micro-photoluminescence (µ-PL) spectroscopy and
(scanning) transmission electron microscopy (S)TEM performed on the same single
semiconductor nanowire (NW) [1] are discussed. Optical measurements comprise
polarization-, temperature-, power- and time-resolved as well as magnetic fielddependent µ-PL where single NWs are preselected with low-voltage STEM and
subsequently measured with various high-voltage TEM techniques such as high-angle
annular dark field (HAADF) STEM, high-resolution TEM and energy dispersive X-ray
spectroscopy (EDX). This method was used to determine the fundamental optical and
electronic properties of wurtzite (WZ) GaAs, a crystal phase exclusively observed in
NWs [2].
Using the combined µ-PL-(S)TEM approach single nearly defect-free Au-assisted
wurtzite core-shell GaAs/AlGaAs NWs were studied to compare their bandgap, exciton
emission energy and suitability for optoelectronics applications with ZB GaAs literature
data. We find a clear difference of ~ 20 meV between the room temperature bandgap of
WZ GaAs at 1.444 eV and the ZB GaAs one at 1.424 eV. Exciton emission energies at
low temperature are strikingly similar (1.515 eV). However, WZ exciton binding energy
as determined with magneto-µ-PL is ~ 3 meV larger, thus suggesting a low T bandgap of
1.522 eV for WZ GaAs versus the well-known 1.519 eV for ZB GaAs.
Conduction band symmetry and optical quality of the Au-assisted MBE grown GaAs
NWs are discussed based on temperature- and time-resolved µ-PL measurements.
Importantly, Au-assisted MBE grown GaAs NWs are found to be comparable to current
state-of-the-art self-assisted GaAs NWs in terms of integrated PL signal at room
temperature and quantum efficiency, contrary to previous reports [3]. Measurements on
self-catalyzed zincblende (ZB) GaAs/AlGaAs core-shell NWs are currently in progress in
order to extend this study to a direct comparison between the two types of GaAs NWs.
References:
[1] J. Todorovic, A.F. Moses, T. Karlberg, P. Olk, D.L. Dheeraj, B.O. Fimland, H.
Weman and A.T.J. van Helvoort, Nanotechnology 22 325707 (2011)
[2] L. Ahtapodov, J. Todorovic, P. Olk, T.S. Mjaaland, P.R.T. Slaattnes, D.L. Dheeraj,
A.T.J. van Helvoort, B.O. Fimland and H. Weman (unpublished)
[3] S. Breuer, C. Pfuller, T. Flissikowski, O. Brandt, H.T. Grahn, L. Geelhaar and H.
Riechert, Nano Lett., 2011, 11 (3), 1276-1279