Method of determining potential barrier heights at submonolayer AlAsÕGaAs heterointerfaces
Gil-Ho Kim
Telecommunication Basic Research Laboratory, ETRI, Yusong P.O. Box106, Taejon305 – 600, Korea
and Cavendish Laboratory, Madingley Road, Cambridge CB3 OHE, United Kingdom
M. Y. Simmons
Semiconductor Nanofabrication Facility, School of Physics, University of New South Wales, Sydney 2052, Australia
C.-T. Liang
Department of Physics, National Taiwan University, Taipei106, Taiwan
D. A. Ritchie and A. C. Churchill*
Cavendish Laboratory, Madingley Road, Cambridge CB3 OHE, United Kingdom
H.-S. Sim and K. J. Chang
Department of Physics, Korea Advanced Institute of Science and Technology, Taejon305 – 701, Korea
G. Ihm and N. Kim
Department of Physics, Chungnam National University, Taejon 305 – 764, Korea
Received 20 July 2001; published 5 October 2001
We report low-field magnetoresistance measurements of a two-dimensional electron gas formed in a GaAs
quantum well, in which half a monolayer of AlAs has been inserted into the center of the well. A large
anisotropy is observed in both the mobility and the low field magnetoresistance in the orthogonal 1
¯
10 and
110 directions. We describe a method of using the anisotropic low field magnetoresistance to calculate the
magnitude of the effective potential of the AlAs submonolayer at the GaAs/AlGaAs heterointerface.
DOI: 10.1103/PhysRevB.64.165313 PACS numbers: 73.21.-b, 73.40.-c, 73.61.-r, 73.50.Jt
The ability to control the electronic potential at a semi-
conductor heterostructure interface is important for studies of
systems such as lateral superlattices, one-dimensional 1D
quantum wires and single quantum wells. A standard method
of controlling the potential at a heterostructure interface is to
use a metallic Schottky gate on the surface of the device
produced by a technique such as electron beam lithography
EBL. A good example of this is the transport properties of
a 1D periodic potential formed by the use of a grating gate
fabricated using EBL, which has attracted much interest both
experimentally
1–4
and theoretically.
5–7
Another potentially
significant route for the fabrication of one-
8,9
and zero-
dimensional
10,11
nanostructures is by natural formation dur-
ing the growth procedure. Whilst there are a few studies of
the physics of such systems
12–16
there is a notable dearth in
the literature of detailed magnetotransport measurements of
naturally formed submonolayer potential heterostructures.
In this paper we present detailed magnetotransport studies
of a two-dimensional electron gas 2DEG in a GaAs quan-
tum well in which half a monolayer of AlAs has been in-
serted into the center of the well. Using a full surface
Schottky gate it is possible to control the carrier density of
the 2DEG in the well and observe the effect of the AlAs
potential on the magnetoresistance in both the 110 and
1
¯
10 directions. Previous studies of the magnetoresistance
of a 2DEG with a periodic potential, created with a Schottky
grating gate, showed that electrons are trapped in potential
energy minima below a critical magnetic field.
2–4
By altering
the voltage on the grating gate it was possible to control the
potential energy at the heterointerface and thereby tailor the
electrical properties of the 2DEG. In our devices we measure
the magnetoresistance characteristics of a naturally formed
1D periodic potential with a fixed effective potential energy
due to the incorporation of a submonolayer of AlAs. The
results demonstrate the anisotropic nature of this fixed 1D
periodic potential associated with the formation of elongated
AlAs islands in the 1
¯
10 direction within the GaAs quan-
tum well.
Figure 1a shows a schematic cross-sectional illustration
of our device, a n-AlGaAs/GaAs heterojunction grown by
molecular beam epitaxy on an undoped GaAs 001 substrate
deliberately misoriented by 0.09°. The structure consists of a
0.6 m thick undoped GaAs buffer layer, followed by a
500 Å undoped Al
0.33
Ga
0.67
As barrier, a 200 Å undoped
GaAs quantum well, a 400 Å undoped Al
0.33
Ga
0.67
As spacer
layer, a 400 Å Si-doped (1 10
18
cm
-3
) Al
0.33
Ga
0.67
As
layer, and finally a 170 Å GaAs capping layer. Results are
presented from two different samples. In sample A, an AlAs
layer with a coverage of approximately 0.5 monolayers ML
was inserted into the GaAs quantum well using the migration
enhanced step flow growth mode described in Ref. 8. Sample
B is a reference sample with the same heterostructure design
grown on an identically misoriented 001 GaAs wafer but
without the AlAs submonolayer insertion.
The devices were processed into an orthogonal Hall bar
geometry in Fig. 1c, with the current in either the 110
and 1
¯
10 direction, with a width of 80 m and a length of
PHYSICAL REVIEW B, VOLUME 64, 165313
0163-1829/2001/6416/1653135/$20.00 ©2001 The American Physical Society 64 165313-1