COL 9(4), 041601(2011) CHINESE OPTICS LETTERS April 10, 2011
Stacking-faults-free zinc blende GaAs/AlGaAs axial
heterostructure nanowires during vapor-liquid-solid growth
Jingwei Guo (HHH²²²)
∗
, Hui Huang ( ), Xiaomin Ren (???¡¡¡¯¯¯), Xin Yan (ôôô ccc),
Shiwei Cai (ééé), Yongqing Huang ([[[), Qi Wang ( lll),
Xia Zhang (ÜÜÜ ___), and Wei Wang ( )
Key Laboratory of Information Photonics and Optical Communications, Ministry of Education,
Beijing University of Posts and Telecommunications, Beijing 100876, China
∗
Corresp onding author: guojingwei666@163.com
Received September 27, 2010; accepted December 7, 2010; posted online March 15, 2011
Pure zinc blende structure GaAs/AlGaAs axial heterostructure nanowires (NWs) are grown by metal
organic chemical vapor deposition on GaAs(111) B substrates using Au-catalyzed vapor-liquid-solid mech-
anism. Al adatom enhances the influence of diameters on NWs growth rate. NWs are grown mainly
through the contributions from the direct impingement of the precursors onto the alloy droplets and not
so much from adatom diffusion. The results indicate that the droplet acts as a catalyst rather than an
adatom collector.
OCIS codes: 160.4236, 310.3840.
doi: 10.3788/COL201109.041601.
In the past few years, semiconductor nanowires (NWs)
have attracted a great deal of interest due to their
potential applications in electronic and optoelectronic
devices
[1,2]
. The Au-catalyzed vapor-liquid-solid (VLS)
mechanism is a commonly used method for semicon-
ductor NW growth
[3,4]
. At growth temperature, Au
nanoparticles (NPs) on the substrate surface form alloy
droplets with the group III growth precursor(s). Semi-
conductor NWs are grown from supersaturated alloy
droplets.
GaAs/AlGaAs heterostructure NWs are one of the
most popular NWs. GaAs and AlGaAs have al-
most the same lattice constant, and the difference be-
tween their band gaps and refractive indices is large,
which is advantageous for applications in optoelectronic
devices
[5,6]
. However, many studies have focused on the
GaAs/AlGaAs radial heterostructure
[7−13]
, which is a
core-shell structure, and little research has been con-
ducted on the GaAs/AlGaAs axial heterostructure. In
this letter, the growth of Au-assisted GaAs/AlGaAs ax-
ial heterostructure NWs is investigated, and the related
growth mechanism is discussed.
The growth was performed in a Thomas Swan close
coupled showerhead metal-organic chemical vapor depo-
sition (CCS-MOCVD) system at a pressure of 100 torr.
Trimethylgallium (TMGa, 4×10
−5
mol/min) and AsH
3
(2.8×10
−3
mol/min) were precursors for GaAs growth.
When AlGaAs was grown, trimethylaluminum (TMAl,
4×10
−5
mol/min) was introduced with the same TMGa
and AsH
3
flows. The carrier gas was hydrogen.
Prior to growth initiation, an Au film with a thickness
of 4 nm was deposited on the GaAs (111) B substrate by
magnetron sputtering. The Au-coated substrate was
then loaded into the MOCVD reactor and annealed
in situ at 650
◦
C in arsine and hydrogen ambient for
the desorption of surface contaminants and the forma-
tion of alloy droplets as catalyst. After ramping down to
the growth temperature, GaAs NWs were firstly grown
for 600 s at 440
◦
C, which is the optimum temperature
based on a number of experiments (at a lower tempera-
ture NWs will be kinked; at a higher temperature, taper
will occur). Five pairs of AlGaAs (10 s)/GaAs (10 s)
heterostructure junctions were grown at the same tem-
perature.
The morphologies of as-grown NWs were studied us-
ing a HITACHI S-5500 field-emission scanning electron
microscope (SEM). The structure and chemical compo-
sitions of a single NW were characterized using an FEI
TECNAI F30 field-emission transmission electron mi-
croscope (TEM) equipped with energy dispersive X-ray
spectroscopy (EDS) as well as a scanning transmission
electron microscope (STEM). For the preparation of
TEM samples, the NWs were removed from the sub-
strate by sonication into ethanol suspension for 2 min. A
small volume of the NW suspension was left to dry onto
a holey carbon film supported by a Cu mesh TEM grid.
Cross-sectional views of the SEM images of the grown
NWs are shown in Fig. 1. All NWs are vertical to the
substrate. There are five junctions in each NW because
of the changes in the volume of the alloy droplets at the
tip of the NWs caused by different supersaturations of
Ga and Al dissolved in Au NPs. The supersaturation of
Fig. 1. (a) Sketch of the proposed NW configuration; (b)
cross-section view of the SEM image of GaAs/AlGaAs NWs.
The inset is a magnified pattern of the top segment of one
NW.
1671-7694/2011/041601(4) 041601-1
c
° 2011 Chinese Optics Letters