Structural properties of Bi2Te3 and Bi2Se3 topological insulators grown by molecular
beam epitaxy on GaAs(001) substrates
X. Liu, D. J. Smith, J. Fan, Y.-H. Zhang, H. Cao, Y. P. Chen, J. Leiner, B. J. Kirby, M. Dobrowolska, and J. K.
Furdyna
Citation: Applied Physics Letters 99, 171903 (2011); doi: 10.1063/1.3655995
View online: http://dx.doi.org/10.1063/1.3655995
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APPLIED PHYSICS LETTERS 99, 171903 (2011)

Structural properties of Bi2Te3 and Bi2Se3 topological insulators grown by
molecular beam epitaxy on GaAs(001) substrates
X. Liu,1,a) D. J. Smith,2 J. Fan,2,3 Y.-H. Zhang,3,4 H. Cao,5 Y. P. Chen,5 J. Leiner,1 B. J. Kirby,6
M. Dobrowolska,1 and J. K. Furdyna1
1

Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA
Department of Physics, Arizona State University, Tempe, Arizona 85287, USA
3
Center for Photonics Innovation, Arizona State University, Tempe, Arizona 85287, USA
4
School of Electrical, Computer and Energy Engineering, Arizona State University, Tempe, Arizona 85287, USA
5
Department of Physics, Purdue University, West Lafayette, Indiana 47907, USA
6
Center for Neutron Research, NIST, Gaithersburg, Maryland 20899, USA
2

(Received 20 July 2011; accepted 4 October 2011; published online 24 October 2011)
Thin films of Bi2Te3 and Bi2Se3 have been grown on deoxidized GaAs(001) substrates using
molecular beam epitaxy. Cross-sectional transmission electron microscopy established the highly
parallel nature of the Te(Se)-Bi-Te(Se)-Bi-Te(Se) quintuple layers deposited on the slightly wavy
GaAs substrate surface and the different crystal symmetries of the two materials. Raman mapping
confirmed the presence of the strong characteristic peaks reported previously for these materials in
bulk form. The overall quality of these films reveals the potential of combining topological
C 2011 American Institute of
insulators with ferromagnetic semiconductors for future applications. V
Physics. [doi:10.1063/1.3655995]

Recent photoemission measurements of the surfaces of
topological insulators (TIs) such as Bi1xSbx, Bi2Te3 and
Bi2Se3 have confirmed that a conducting surface state with
an odd number of Dirac points exists in these materials.1
Theoretical models of topological insulators have predicted
that this surface state should be robust and “topologically
protected.”1 Moreover, this conducting state is naturally
spin-polarized, which opens up interesting opportunities for
possible applications in spintronics.2 The growth of such topological insulators by molecular beam epitaxy (MBE) is
especially attractive because of the possibility to avoid defect
formation by controlling the growth conditions. Efforts to
fabricate TI thin films by MBE have included growth of
Bi2Te3 on substrates of Si(111),3,4 and growth of Bi2Se3 on
substrates of graphene,3 Si(111),5,6 as well as GaAs(111).7
Because representative spintronic materials, such as GaMnAs, are easily grown on GaAs (001) substrates,8 and Fe
films of very high crystalline perfection can also be grown
on GaAs (001) or (110) substrates,9 we are actively pursuing
MBE growth of Bi2Te3, Bi2Se3 and their alloys on GaAs
(001) substrates, with a goal to combine these electronic
materials into multifunctional device configurations in the
future. We demonstrate here that MBE growth of pseudohexagonal Bi2Te3 and Bi2Se3 thin films can also be achieved
on GaAs (001) substrate despite the very different crystal
symmetries along the film growth direction.
The Bi2Te3 and Bi2Se3 films were grown using a dualchamber MBE system, with the growth process being monitored in situ by reflection-high-energy electron diffraction
(RHEED). The growth sequence was usually as follows.
First, the epi-ready GaAs (001) semi-insulating substrates
were heated up to 600  C for surface deoxidation. This deoxidation process was done either in the II–VI MBE chamber,

which was also equipped with high purity Bi, Te, and Se
evaporators or, alternatively, in the III–V MBE chamber by
depositing a 100-nm GaAs buffer layer on the deoxidized
GaAs substrate, which was then transferred via an ultrahighvacuum load-lock assembly into the II–VI MBE chamber.
The TI growth was initiated by the deposition of a sequence
of either Te-Bi-Te-Bi-Te or Se-Bi-Se-Bi-Se atomic layers at
room temperature. During this process, the (2  4) RHEED
pattern disappeared, indicating that an amorphous film had
been deposited. The substrate was then gradually heated to
about 300  C to anneal the film, and a streaky RHEED pattern shown in Fig. 1 became visible, indicating that a quintuple layer (QL) of TI film had been formed.5 It is important to
note that the RHEED pattern showed recurrences six times
during each rotation of the substrate, which confirms the caxis growth of the pseudo-hexagonal TI films, with the aaxis lying along either the [110] or the ½110 direction of the
GaAs (001) substrate. Two types of RHEED patterns were
observed in this stage, depending on the length of annealing

a)

FIG. 1. RHEED patterns observed for two specific orientations of GaAs
(001) substrate during MBE growth of (a) Bi2Te3 and (b) Bi2Se3.

Author to whom correspondence should be addressed. Electronic mail:
xliu2@nd.edu.

0003-6951/2011/99(17)/171903/3/$30.00

99, 171903-1

C 2011 American Institute of Physics
V

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Liu et al.

time. As shown in Fig. 1(a), usually observed in Bi2Te3 case
(QL of Bi2Te3 usually survives for a longer annealing time
than Bi2Se3), longer annealing times yielded an unreconstructed pattern with distinct features observed for GaAs
[110] and ½1
10 directions, respectively. We attribute this to
the hexagonal surface symmetry of the TI layer. On the other
hand, short annealing times yielded the same RHEED patterns for both GaAs [110] and ½110 directions, as shown in
Fig. 1(b), which is often observed for Bi2Se3. Note that the
RHEED pattern is actually a combination of the two distinct
patterns seen on the [110] and ½110 directions in the long
annealing case. We therefore attribute this to the coexistence
of two types of hexagonal surfaces perpendicular to each
other. The MBE growth of Bi2Te3 and Bi2Se3 was then performed under the condition of TTe (or TSe) < Tsubstrate
(300  C) < TBi (500  C) with a Se(or Te):Bi beam equivalent
pressure ratio ranging from 15:1 to 25:1. While no notable
differences were observed for the growth of Bi2Te3 and
Bi2Se3 when carried out on substrates with or without the
GaAs buffer layer, the results described here refer only to TI
films grown without the buffer layers. The TI thin films were
grown layer-by-layer, with typical growth rates in this work
of 2 QL/min, as characterized by RHEED oscillations (data
not shown). RHEED patterns shown in Fig. 1 were maintained throughout the whole growth process. It should be
emphasized that the same kind of growth is also observed on
the Ga-rich GaAs (001) surfaces, i.e., surfaces with a (4  6)
RHEED pattern. We therefore attribute the growth of
pseudo-hexagonal Bi2Te3 and Bi2Se3 on the GaAs (001) substrates to the weak Van der Waals coupling between the substrate and the TI films, leading to immediate strain relaxation
as the interface is forming.3–7
The film thicknesses were determined ex situ through
model-fitting10 of the specular x-ray reflectivity (XRR), as
shown by the example (thickness 68 nm) in Fig. 2. These
thickness values were in reasonable agreement with the
growth rates that were estimated in situ from RHEED oscillations. The standard deviation of film thickness obtained by
fitting the XRR data was about 2.3 nm (3% of thickness),
which suggests the root-mean-square roughness average
(RMA) will be of the same order as that reported for the TI
films of comparable thickness grown on other substrates.4

FIG. 2. (Color online) Model-fitted specular x-ray reflectivity of the Bi2Te3
film, used for estimating the film thickness. Error bars correspond to 61r.

Appl. Phys. Lett. 99, 171903 (2011)

FIG. 3. X-ray diffraction patterns obtained from (a) 233-nm-thick Bi2Te3
film and (b) 130-nm-thick Bi2Se3 film grown by MBE on GaAs(001)
substrate.

The overall crystallinity of the TI films was initially evaluated by high resolution x-ray diffraction (HR-XRD) using
the Cu Ka1 radiation line. Figure 3 shows XRD patterns that
were obtained from: (a) a 233-nm-thick Bi2Te3 film and (b)
a 180 nm-thick Bi2Se3 film, respectively. Strong reflections
only from {003}-type lattice planes are visible, which is
indicative of the highly pronounced c-axis growth of the
film. The full-width-half-maximum for the (0,0,6) plane
indicates that the crystallinity of Bi2Se3 was considerably
better than that of Bi2Te3 (108 versus 763 s). The QL
thicknesses were calculated from the XRD data,
giving dQL ¼ 1.006 6 0.015 nm for Bi2Te3 and dQL
¼ 0.9527 6 0.0005 nm for Bi2Se3, respectively (uncertainties
correspond to 1r). Both values are consistent with the values
of 1.016 nm for the bulk Bi2Te3 (Ref. 11) and 0.9545 nm for
bulk Bi2Se3.12
The microstructure of the films was determined using
cross-section transmission electron microscopy (XTEM).
Samples were prepared for TEM examination using standard
mechanical polishing and argon-ion-milling, with the sample
held at liquid-nitrogen temperature during the latter process
in order to avoid unintentional ion-milling artifacts. Gentle
handling was necessary because the TI films had a tendency
to peel away from the substrate during the preparation procedure, consistent with weak bonding between the TI films and
the substrate. Figure 4(a) is an XTEM image showing a
region of the Bi2Se3 film close to the GaAs substrate surface.
Despite the slightly wavy surface of the epi-ready GaAs substrate, highly parallel layers are clearly visible in the Bi2Se3
film, suggesting that the high crystal quality is achieved by
an internal self-correction process that is occurring as the
growth proceeds. Figure 4(b) shows an enlarged view of the
Bi2Se3/GaAs interface, which illustrates the pronounced planarity of the Bi2Se3 lattice planes even in close proximity to
the undulating GaAs surface. In addition, atomically sharp
image of XTEM shows no dislocations and accumulated
strain immediately above GaAs, despite the symmetry mismatch between the TI films and the GaAs (001) surface. This

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171903-3

Liu et al.

FIG. 4. Transmission electron microscopy (TEM) images showing cross
sections of topological insulator Bi2Se3 grown by MBE on a deoxidized
GaAs(001) substrate.

observation undoubtedly confirms the rapid relaxation of
strain at the interface, which is similar to what is observed
on graphene and Si.3–7 We attribute such unique feature to
the weak van der Waals coupling between adjacent QLs in
the TI films. TEM images also confirmed that the a-axis of
the pseudo-hexagonal TI films lies along either the [110] or
the ½1
10 direction of the GaAs (001) substrate.
Micro Raman spectroscopy with a 532-nm excitation
laser (power 0.8 mW) was also performed. The results,
shown in Fig. 5, reveal three of the characteristic peaks for
Bi2Se3 [at 71 cm1 (A11g), 131 cm1 (E2g), and 174 cm1
(A21g)], and two of the characteristic peaks for Bi2Te3 [at
102 cm1 (E2g) and 134 cm1 (A21g)]. The peaks observed
in these two TI materials are consistent with the lattice vibration modes reported earlier.13 Moreover, Raman mapping
showed that the positions of these Raman peaks measured
within a scan area of 15 lm  15 lm vary spatially by less
than 1 cm1, indicating a good uniformity of the films.
In summary, even though there is mismatch between the
hexagonal lattices of Bi2Te3 and Bi2Se3 topological insulators and the cubic symmetry of the GaAs (001) surface, we
have grown high quality epitaxial films of Bi2Te3 and Bi2Se3
on GaAs (001) substrates. The films are highly uniform and
the crystallinity is comparable to that of films grown on substrates with hexagonal surface structure. Future studies of
Bi2Te3 and Bi2Se3 grown on GaAs (001) substrates should
contribute towards a better knowledge of MBE growth of
topological insulators, as well as opening up the opportunity
for future spin-based devices that combine topological insulators with ferromagnetic semiconductors.

Appl. Phys. Lett. 99, 171903 (2011)

FIG. 5. Representative Raman spectra measured in MBE films of: (a)
Bi2Te3 and (b) Bi2Se3. The film (a) is 136 nm thick and the film (b) is
150 nm thick.

This work was supported by NSF Grant DMR10-05851
for ND; for ASU an NSF grant, contract number 1002114
and an AFOSR Grant number FA9550-10-1-0129; Y.P.C.
acknowledges support from DARPA MESO program. The
authors acknowledge use of facilities in the John M. Cowley
Center for High Resolution Electron Microscopy at Arizona
State University and the x-ray reflectometer at the NIST
Center for Neutron Research.
1

M. Z. Hasan and C. L. Kane, Rev. Mod. Phys. 82, 3045 (2010).
S.-C. Zhang, Physics 1, 6 (2008).
3
X. Chen, X.-C. Ma, K. He, J.-F. Jia, and Q.-K. Xue, Adv. Mater. 23, 1162
(2011).
4
J. Krumwain, G. Mussler, S. Borisova, T. Stoica, L. Plucinski, C. M.
Schneider, and D. Grützmacher, J. Cryst. Growth 324, 115 (2011).
5
G. Zhang, H. Qin, J. Teng, J. Guo, Q. Guo, X. Dai, Z. Fang, and K. Wu,
Appl. Phys. Lett. 95, 053114 (2009).
6
H. D. Li, Z.Y. Wang, X. Guo, T. L. Wong, N. Wang, and M. H. Xie, Appl.
Phys. Lett. 98, 043104 (2011).
7
A. Richardella, D. M. Zhang, J. S. Lee, A. Koser, D. W. Rench, A. L.
Yeats, B. B. Buckley, D. D. Awschalom, and N. Samarth, Appl. Phys.
Lett. 97, 262104 (2010).
8
J. Sadowski, R. Mathieu, P. Svedlindh, J. Z. Domagała, J. Bak-Misiuk, K.
Światek, M. Karlsteen, J. Kanski, L. Ilver, H. Åsklund, and U. Södervall,
Appl. Phys. Lett. 78, 3271 (2001).
9
J. J. Krebs, B. T. Jonker, and G. A. Prinz, J. Appl. Phys. 61, 2596 (1987).
10
P. A. Kienzle, M. Doucet, D. J. McGillivray, K. V. O’Donovan, N. F.
Berk, and C. F. Majkrzak, NCNR Reflectometry Software. Available at
the NIST Center for Neutron Research, http://www.ncnr.nist.gov/reflpak.
11
J. O. Jenkins, J. A. Rayne, and J. R. W. Ure, Phys. Rev. B 5, 3171 (1972).
12
S. Nakajima, J. Phys. Chem. Solids 24, 479 (1963).
13
W. Richter, H. Kohler, and C. R. Becker, Phys. Status Solidi. B 84, 619
(1977).
2

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