Book of abstracts - Euro-MBE 2011 - CNRS

Mo1.5
InAs Quantum Dot Chains Grown on Nanoimprint Lithography
Patterned GaAs(100)
T. V. Hakkarainen*, A. Schramm, J. Tommila, A. Tukiainen, R. Ahorinta, M.
Dumitrescu, M. Guina.
Optoelectronics Research Centre, Tampere University of Technology,
P.O. Box 692, FIN-33101 Tampere, Finland.
The ability to fabricate Stranski-Krastanov quantum dots on pre-determined locations, i.e. sitecontrolled
growth, is essential for enabling emerging nanophotonic applications, such as photonic
integrated circuits incorporating quantum dot chains (QDCs) as nanophotonic waveguides. As a
method for the fabrication of site-controlled InAs QDCs, we combine growth by molecular beam
epitaxy and nanoimprint lithography (NIL) [1]. NIL is able to produce sub 10 nm linewidths with high
throughput and enables fast processing of large wafer area.
In this paper we focus on studying structural and optical properties of QDCs with varying orientations
with respect to the substrate crystal directions. The investigated samples were prepared in three stages.
In the first stage, a 100 nm GaAs buffer, a 100 nm AlGaAs layer, and a 100 nm GaAs were deposited
at 590 °C on n-GaAs(100) substrates by MBE. Then grooves were ex situ patterned by UV-NIL. The
groove width was 90 nm, depth 30 nm, and period 180 nm. In the final stage, the patterned surface
was covered with a 60 nm GaAs regrowth buffer at 490 °C and 2.2 ML InAs QDs grown at 515 °C.
For optical investigation, the QDs were covered with GaAs and AlGaAs layers. We show that this
method enables the simultaneous growth of QDCs oriented along [011], [01-1], [010], and [001]
directions (Fig. 1) exhibiting strong photoluminescence (PL) emission at room temperature. Being
able to form QDCs with different orientations with at the same growth conditions is crucial for the
fabrication of QDC networks for integrated circuits. Furthermore, we report low temperature PL
(temperature, power, and polarization dependencies) for the optical characterization of the QDCs and
atomic force microscopy (AFM) based facet analysis for investigating the morphology of the patterned
surface.
(a)
(c)
[011]
(b)
(d)
[01-1]
PL intensity (arb. units)
1.0
0.8
0.6
0.4
0.2
0.0
[0-11]
[011]
[0-1-1]
[01-1]
4.5 mW
1.2 mW
0.7 mW
0.1 mW
1.1 1.2 1.3 1.4
Energy (nm)
Fig. 1. AFM pictures of QDCs grown on a groove
pattern oriented along [011] (a), [01-1] (b), [010] (c),
and [001] (d) directions.The color scale in (a)-(d) is 26
nm.
Fig. 2. PL spectra from [01-1]-oriented QDCs measured at
10K with different excitation laser powers. The inset
shows polarization anisotropy of the PL emission. The
radial axis of the polar plot represents relative PL intensity
ranging from 0.9 to 1.1
[1] J. Tommila, A. Tukiainen, J. Viheriälä, A. Schramm, T. Hakkarainen, A. Aho, P. Stenberg, M. Dumitrescu and M. Guina,
”Nanoimprint lithography patterned GaAs templates for site-controlled InAs quantum dots”, to be published in J. Cryst.
Growth.
_________________________
* Contact: teemu.hakkarainen@tut.fi