JAIST Repository
https://dspace.jaist.ac.jp/Title

Spin splitting in InGaSb/InAlSb 2DEG having highindium contentAuthor(s)Akabori, M; Sunouchi, T; Kakegawa, T; Sato, T;
Suzuki, T; Yamada, SCitation

Physica E: Low‑dimensional Systems andNanostructures, 34(1‑2): 413‑416

Issue Date

2006‑08

Type

Journal Article

Text version

author

URL

http://hdl.handle.net/10119/3327

RightsElsevier B.V., Masashi Akabori, Takashi Sunouchi,Tomoyasu Kakegawa, Taku Sato, Toshi‑kazu Suzuki
and Syoji Yamada, Physica E: Low‑dimensional
Systems and Nanostructures, 34(1‑2), 2006, 413‑416.
http://www.sciencedirect.com/science/journal/1386
9477

Description

Japan Advanced Institute of Science and Technology

Spin splitting in InGaSb/InAlSb 2DEG having high indiumcontent
Masashi Akabori*, Takashi Sunouchi, Tomoyasu Kakegawa, Taku Sato,Toshi-kazu Suzuki, Syoji Yamada
Center for Nano-Materials and Technology (CNMT), Japan Advanced Institute of Science and Technology (JAIST), 1-1, Asahidai, Nomi,
Ishikawa 923-1292, JAPANElsevier use only: Received date here; revised date here; accepted date here

Abstract
We formed a novel metamorphic InGaSb/InAlSb two-dimensional electron gas (2DEG) having high indium contents around
0.9 by molecular beam epitaxy (MBE), and investigated its spin splitting through magneto-resistance (MR) characteristics byusing Hall-bar samples. We observed clear Shubnikov-de Haas (SdH) type MR oscillations with some peak splitting inducedby the Zeeman-like spin splitting over B=1 T at 1.5K. An Estimated splitting energy, ∆E, was 9 meV at B=4 T for the Landauindex, n=1. Moreover, we also observed no peak splitting, i.e. spin split vanishing around B=1 T. Additionally, we confirmed
some SdH beat patterns due to the zero-field spin splitting less than B=1 T, and the splitting energy at B=0, ∆E0, wasestimated to be 4~6 meV from the SdH fast Fourier transform (FFT) analysis. We successfully demonstrated well fitting
curves for the Landau plots of SdH peaks across B=1 T, thus the Zeeman-like splitting, the spin split vanishing, and the beatpatterns due to the zero-field splitting can be connected, smoothly. The fitting curves were obtained by assuming not theRashba effect but the Dresselhaus effect on the (001) surface with the confinement. Therefore, it suggests that the zero-field
spin splitting in the present InGaSb/InAlSb 2DEG originates from the Dresselhaus effect. © 2001 Elsevier Science. All rights
reserved
PACS: 71.70.Ej; 73.61.Ey
Keywords: InGaSb/InAlSb two-dimensional electron gas (2DEG); Zeeman spin splitting; Spin split vanishing; Zero-field spin splitting

1. Introduction
Narrow gap semiconductor (NGS) twodimensional electron gases (2DEGs) are applicable tonon-magnetic semiconductor spin devices, e.g. thespin field effect transistors (spin-FETs) proposed byDatta and Das [1], because such NGS-2DEGs are
possible to show large zero-field spin splitting [2-5],

which is necessary to control spin polarized electrons
in the spin-FETs. Previously, we have formed
metamorphic InGaAs/InAlAs 2DEGs with highindium contents over 75% [6], and have investigatedtheir transport properties including some spin
splitting [7-8]. Our 2DEGs have high mobility(µ~4×105cm2/Vs) and large SO interaction (α~3×1011eVm) at low temperatures.
In this work, we have formed and investigated anovel metamorphic InGaSb/InAlSb 2DEG having

2Submitted to Elsevier Scienceindium contents around 0.9, which is anotherimportant candidate of NGS-2DEGs.

2. Experimental procedure
Figure 1 shows schematic illustrations of theInGaSb/InAlSb 2DEG structure. We grew the 2DEG
on a semi-insulating GaAs (001) by a conventional
molecular beam epitaxy (MBE) with a Sb cracker
cell. The indium contents for the InGaSb and theInAlSb were fixed to 0.89 and 0.88, respectively. To
reduce threading dislocations, a 6µm-thick InAlSb
buffer layer was grown on the GaAs, directly. The
thickness of the InGaSb channel layer was 30 nm,
and the depth of the 2DEG interface was about 160
nm. The detail of the MBE growth and the influenceof the threading dislocations will be discussed
elsewhere [9].
After the growth, we fabricated some Hall-bar
samples by using conventional photolithography
techniques. The channel width was 50 µm, and theprobe distance was 200µm. The channel directions
were defined to [110], [-110] and [010] for theinvestigation of some transport anisotropy. By using
the Hall-bar samples, we measured magnetotransports at 1.5K in a liquid He cryostat with asuperconducting magnet. For the measurements, weused an AC lock-in setup. The typical current was
100 nA.

3. Experimental results and discussions
We summarized the sheet electron concentration
NS and the mobility µ for various channel directionsin Table 1, which were estimated from Hallmeasurements at magnetic field B=0.3 T. Sometimes
there is a large mobility anisotropy (almost twice) insuch metamorphic 2DEGs [10], however, themobility anisotropy in our present 2DEG was 13% i.e.
not so large. Additionally, the sheet electron
concentration was almost similar value around
2.7×1011cm-2. Therefore, the results indicate that ourpresent 2DEG has high quality.
Figure 2 shows a magneto-resistivity (MR) ρxx
curve and Hall-resistivity ρxy curve of the [110]channel sample as a function of magnetic fields. We

observed the Zeeman-like splitting in ρxx and somequantum Hall plateaus in ρxy over B=1 T, whichcorresponded to the Landau index n<5. We note thatthe samples with other channel directions showedsimilar behavior, i.e. almost isotropic properties. Thespin splitting energy ∆E at B=4 T was estimated to beabout 9 meV from the Zeeman-like splitting for n=1.
Such large value indicates that our present 2DEG has
a large effective g factor. Moreover, we could notobserve clear Zeeman-like splitting for n=5-7 around
B=1 T. Thus the spin splitting seemed to be vanishedaround B=1 T.
In order to investigate the detail of the MR under
low magnetic fields, we analyzed the second
derivative of MR oscillations at B<1 T as shown inFig. 3. We could observe a small splitting of peak for
n=6, however, could not find such peak splitting for
n=7-8. Under lower magnetic fields i.e. n>8, wecould find some beating patterns of the MR
amplitude. The amplitude modulation can beunderstood as the zero-field spin splitting. Throughthe fast Fourier transform (FFT) analysis [5, 7-8], we
obtained that the zero-field spin splitting energy wasestimated to be ∆E0=4~6 meV.
In order to understand the connection of the spin
splitting between the Zeeman dominant region andthe zero-field dominant region, we plotted theLandau index with two kinds of fitting curves as afunction of inverse magnetic fields B-1 as shown inFig. 4. The fitting curves were calculated byassuming two kinds of inversion asymmetry effects
as follows; one is the Rashba effect, and the other isthe Dresselhaus effect. We neglected the contributionof kF3 term (kF: the Fermi wave vector), which was
not dominant at the present, therefore we consideredthe Dresselhaus effect only on the (001) surface withthe 2DEG confinement. The Hamiltonian and thezero-field spin splitting energy for the Rashba effect[2-4] are written as
HR=α(σxky-σykx),(1)∆E0=2αkF,(2)

and those for the Dresselhaus effect [3] are written as
HD=β(σyky-σxkx),(3)∆E0=2βkF.

(4)

Submitted to Elsevier Science

α and β are the SO coupling parameters. σx and σy are
the Pauli spin matrices. kx and ky are the wave vector
components in the 2DEG plane. By using the ∆E0, thespin split Landau levels En± including SO interaction
can be described as
En±=ħωc(n±½ ((1-ν0)2+n∆E02/EFħωc)½)(5)

3vanishing spin splitting around B=1 T, and some SdHbeat patterns due to the zero-field spin splitting lessthan B=1 T. By assuming the Dresselhaus type zerofiled spin splitting, we successfully demonstrated thesmooth transition between the Zeeman effect and theDresselhaus effect.

for the Rashba effect andEn±=ħωc(n±½ ((1+ν0)2+n∆E02/EFħωc)½)(6)

for the Dresselhaus effect, whereωc=eB/m*,(7)ν0= gm*/2m0.

(8)

EF is the Fermi energy, which can be estimated fromNS and the effective mass m*. g is the bulk g factor,
and m0 is the electron mass. For the calculation of thefitting curves, we used NS and ∆E0 values estimatedfrom the FFT analysis of low magnetic field
properties. m* was assumed to be 0.023m0, which wasestimated from the cyclotron resonance absorption
experiment [11], and g was assumed to be -51 of bulk
InSb value. The fitting curves assuming the Rashba
effect (dash lines) have no crossing, and do not fit theexperimental results. In contrast, the fitting curves
assuming the Dresselhaus effect (solid lines) have acrossing point, and fit the experimental results very
well from high magnetic fields to low magnetic fields.
The fact indicates that the dominant zero-field spin
splitting should be not the Rashba effect but theDresselhaus effect in the present InGaSb/InAlSb
2DEG. However, underlying mechanism is not wellunderstood. The present results also suggest that it ispossible to obtain zero-field spin splitting energy ∆E0from high magnetic field properties, i.e. the transitionof Zeeman-like spin splitting without beat patternanalysis, which is widely carried out [2-5, 7-8].

4. Summary
We formed a novel metamorphic InGaSb/InAlSb
2DEG having indium contents around 0.9, andcharacterized its spin splitting through a MRmeasurement. We observed clear SdH oscillations
with some peak splitting induced by the Zeeman-likespin splitting over B=1 T, no peak splitting i.e.

Acknowledgement
This work is partially supported by a Grant-in-Aidfor Scientific Research in Priority Areas“Semiconductor Nanospintronics” (No.14076213) ofThe Ministry of Education, Culture, Sports, Scienceand Technology, Japan, and by Mitsubishi, SCAT
Foundations for Science and Technology.

References[1] S. Datta and B. Das, Appl. Phys. Lett. 56 (1990) 665.
[2] J. Luo, H. Munekata, F. F. Fang, P. J. Stiles, Phys. Rev. B 41(1990) 7685.
[3] B. Das, S. Datta, R. Reifenberger, Phys. Rev. B 41 (1990) 8278.
[4] J. Nitta, T. Akazaki, H. Takayanagi, T. Enoki, Phys. Rev. Lett.
78 (1997) 1335.
[5] Th. Schäpers, G. Engels, J. Lange, Th. Klocke, M. Hollfelder,H. Lüth, J. Appl. Phys. 83 (1998) 4324.
[6] S. Gozu, C. Hong, S. Yamada, Jpn. J. Appl. Phys. 37 (1998)
L1501.
[7] Y. Sato, T. Kita, S. Gozu, S. Yamada, J. Appl. Phys. 89 (2001)
8017.
[8] T. Kita, Y. Sato, S. Gozu, S. Yamada, Physica B 298 (2001) 65.
[9] T. Sato, T. Suzuki, S. Tomiya, S. Yamada, “Dislocation-limited
electron transport in InSb and InGaSb/InAlSb grown on
GaAs(001)”, The 23rd International Conference on Defects in
Semiconductors, to appear (2005).
[10] T. D. Mishima, J. C. Keay, N. Goel, M. A. Ball, S. J. Chung,M. B. Johnson, M. B. Santos, J. Cryst. Growth 251 (2003)
551.
[11] K. Fujii, Y. Hachizawa, K. Ohnishi. T. Sato, T. Suzuki, S.
Yamada, S. Gozu, “Investigation of electron spin states in
InGaAs/InAlAs and InGaSb/InAlSb heterostructures”,
Proceedings of 12th International Conference on Narrow Gap
Semiconductors, to appear (2005).

Submitted to Elsevier Science4

Table 1. The sheet electron concentration and the mobility forvarious channel directions estimated from Hall measurement at
1.5K.

Channeldirection[110][-110][010]

Sheet electron
concentration
NS(cm-2)
2.81×1011
2.62×1011
2.71×1011

Mobilityµ(cm2/Vs)
88200
98600
97600

Fig. 3. Second derivative curve of magneto-resistivity as a functionof inverse magnetic fields.

Fig.1. Layer and band structures of the InGaSb/InAlSb twodimensional electron gas wafer.

Fig. 4. Landau plots of magneto-resistivity peaks. Solid lines
indicate the fitting curves assuming the Dresselhaus effect, anddashed lines indicate the fitting curves assuming the Rashba effect.

Fig. 2. Magneto-resistivity and Hall-resistivity curves of a [110]channel Hall-bar as a function of magnetic fields.