G. J. Salamo

J. Wu

V. Dorogan

V. P. Kunets

Y. I. Mazur

Y. Z. Xie

Z. M. Wang

Springer - Publisher Connector

Multiple stacking of InGaAs/GaAs (731) nanostructures

Xie et al                                                  1                                  Nano-Micro Lett. 1, 1-3 (2009) 
NANO-MICRO LETTERS Vol. 1, No. 1  1-3 (2009) 
Multiple stacking of InGaAs/GaAs (731) nanostructures 
Y. Z. Xie, V. P. Kunets, Z. M. Wang*, V. Dorogan, Y. I. Mazur, J. Wu and G. J. Salamo 
We studied the multilayering effects of InGaAs quantum dots (QDs) on GaAs(731), a surface  lying inside of the 
stereographic triangle. The surfaces after stacking 16 InGaAs layers were characterized with highly 
non-uniformity of QD spatial distribution. The bunched step regions driven by strain accumulation are decorated 
by QDs, therefore GaAs(731) becomes a good candidate substrate for the growth of QD clusters. The unique 
optical properties of the QD clusters are revealed by photoluminescence measurements. By adjusting the coverage 
of InGaAs, a bamboo-like nanostructured surface was observed and the quantum dots aligned up in clusters to 
separate the “bamboo” into sections. 
Keywords: Quantum dots; MBE; High index surfaces; Nanostructures; Atomic force microscopy 
Citation: Y. Z. Xie, V. P. Kunets, Z. M. Wang, V. Dorogan, Y. I. Mazur, J. Wu and G. J. Salamo, “Multiple stacking of 
InGaAs/GaAs(731) nanostructures”, Nano-Micro Lett. 1, 1-3 (2009). doi: 10.5101/nml.v1i1.p1-3
The morphological evolution during InGaAs deposition on 
GaAs high index surfaces has been a subject of numerous 
experimental efforts for better understanding of growth physics 
and potential applications of the resulted nanostructures [1-8]. 
Most of the researches chose a surface index located between 
two low index planes out of the three, (100), (110), and (111). 
In other words, the popular choice was a surface index on the 
sides of the stereographic triangle defined by the three low 
index planes [3]. For example, GaAs(311), one of the most 
popular choice, locates between the (100) and (111) planes. 
Both quantum wires and quantum dots (QDs) were observed 
during the InGaAs growth on GaAs(311) [1, 2, 6, 8]. Especially 
during the processes of stacking multiple layers of 
InGaAs/GaAs(311) QDs, two-dimensional or one-dimensional 
arrays of QDs were achieved [8]. In the letter, we study the 
multilayering effects of InGaAs nanostructures on GaAs(731), a 
surface index lying within the stereographic triangle. The (731) 
plane became particularly interesting after the dominating 
facets of InAs/GaAs(100) QDs were identified to this index [9]. 
Massive amount of investigations have been performed to 
reveal the growth behavior of InGaAs on GaAs(100) due to the 
importance of the resulted QDs for optoelectronic applications 
[10-12].  
Experiments were carried out in a solid source Molecular 
Beam Epitaxy (MBE) 32P Riber system. The adopted 
GaAs(731) substrates were of n-type and epitaxial ready. After 
oxide desorption, a GaAs buffer layer of 500 nm was grown at 
the substrate temperature of 580°C. The GaAs growth rate was 
one monolayer per second (ML/s) under a constant As beam 
equivalent pressure (BEP) of 1×10-5 Torr. Sixteen layers of 7 
ML In0.4Ga0.6As nanostructures were subsequently deposited, 
partitioned by GaAs spacer in different thicknesses, 120 ML, 70 
ML, and 50 ML, respectively. The growth of In0.4Ga0.6As layer 
was performed at 540°C and As BEP of 4.4×10-6 Torr. After the 
growth of first 5 MLs of GaAs spacer, the growth temperature 
was rapidly increased up to 580°C and As BEP was turned back 
to 1×10-5 Torr. One more sample, grown in addition to the 
above series, had the GaAs spacer of 70 ML but the In0.4Ga0.6As 
coverage of 5.7 ML. Following the growths, samples were 
quenched to room temperature and then taken out of the MBE 
chambers for Atomic Force Microscopy (AFM) studies under 
ambient atmosphere. For optical properties of the samples, the 
photoluminescence (PL) measurements were performed at 10 K 
in a closed-cycle helium cryostat. The 532 nm line from a 
Nd:YAG (yttrium aluminum garnet) laser was used for 
continuous-wave (CW) PL excitation. The laser spot diameter 
DOI: 10.5101/nml.v1i1.p1-3                                                                      http://www.nmletters.org 
 Institute of Nanoscale Science and Engineering, University of Arkansas, Fayetteville, AR 72701, USA 
*Corresponding author. Email:zmwang@uark.edu 
Nano-Micro Lett. 1, 1-3 (2009)                                  2                                                  Xie et al 
was of ~20 m and the optical excitation power was in the range 
of 106102 mW. The PL signal from the sample was dispersed 
by a 0.5 m single-grating monochromator and detected by a 
liquid nitrogen (LN)-cooled InGaAs photodiode detector array. 
Figure 1(a) shows an AFM image of the surface 
nanostructures after stacking 16 layers of 7 ML In0.4Ga0.6As 
spaced by 120 ML GaAs interlayer. The surface is characterized 
as QD decorated steps and large terraces free of QDs. While 
(731) was observed as the dominating facets bounding 
InAs/GaAs(100) QDs, the GaAs(731) surface itself is unstable. 
GaAs(11 5 2), just 2.28° away from GaAs(731), has lower 
surface energy according to theoretical calculation and was 
observed to be a stable surface by scanning tunneling 
microscopy (STM) [13]. Therefore, GaAs(731) is better 
described as a vicinal GaAs(11 5 2) surface, with straight steps 
along [-113] and ragged steps along [1-32]. The large terraces 
that are free of QDs shown in Fig. 1(a) resulted from the 
strain-driven step bunching. It is well documented that QDs 
prefer to stepped regions for nucleation and growth, especially 
ragged steps due to its active reaction. The observation in Fig. 
1(a) demonstrates that GaAs(731) is a substrate candidate for 
the growth of InGaAs QD clusters. The corresponding PL 
spectrum from this sample is shown in Fig. 2. The strong and 
sharp peak about 1.38 eV can be assigned to the InGaAs 
wetting layer (WL) covering the whole surface. The assignment 
is consistent with the high peak energy and large terraces 
without QDs. Different from usual QDs reported where the PL 
peak from WL is weak, the carriers excited in 
InGaAs/GaAs(731) WL cannot find nearby QDs to relax and 
therefore recombine in WL giving rise to a strong signal. The 
relatively weak peak around 1.25 eV is expected from the 
clustered QDs.  
 
By reducing the GaAs spacer thickness from 120 ML to 70 
ML, more strain could transmit from the underneath InGaAs 
layer to the subsequent layers. As a result of the strain-driven 
mechanism, Fig. 1(b) reveals that the InGaAs QDs grow bigger 
in size and the free-of-QDs terraces disappear. Consistently, the 
WL peak disappears from its associated PL spectrum in Fig. 2 
and the QD peak around 1.25 eV becomes dominant. Please 
notice, this peak is from 15 buried layers of QDs. The 
luminescence from the exposed layer of surface QDs is usually 
not notable, as in the PL spectrum form the sample with 120 
ML spacer. However, the PL contribution from surface QDs can 
be enhanced as the spacer becomes thinner, as the consequence 
of carrier tunneling from the buried QDs to the surface. In line 
with the literature [6], the new developed PL peak around 1.0 
eV is assigned to the layer of surface QDs.  
With further reducing the GaAs spacer to 50 ML, more 
strain is accumulated to the surface and the QDs further ripe 
and even elongate along [-113], as revealed in Fig. 1(c). Due to 
the thinner spacer, more carriers are able to tunnel from buried 
layers to the surface. The PL peak from surface QDs becomes 
stronger, and eventually dominates the spectrum as shown in 
Fig. 2.  
As noticed, the amount of accumulated strain is the key in 
determining the nanostructure configuration in Fig. 1 and the 
optical properties in Fig. 2. Specially, the sample with less 
accumulated strain shown in Fig. 1(a) demonstrated the 
potential of GaAs(731) for growing QD clusters. Therefore, to 
pursue better QD clusters, we introduce a new sample with less 
InGaAs coverage, 5.7 ML, in order to significantly reduce the 
FIG. 1. 5×5 μm AFM images of InGaAs/GaAs(731) multilayer with GaAs spacer
of 120 ML, 70 ML, and 50 ML, respectively. The scale bar of 500 nm and the
lateral direction of [-113] and [1-32] apply to all three images. 
FIG. 2. PL spectra of InGaAs multilayers spaced by GaAs in different thickness.
DOI: 10.5101/nml.v1i1.p1-3                                                                      http://www.nmletters.org 
Xie et al                                                  3                                  Nano-Micro Lett. 1, 1-3 (2009) 
DOI: 10.5101/nml.v1i1.p1-3                                                                      http://www.nmletters.org 
 
total strain. The result is shown in Fig. 3. Comparing Fig. 3(a) 
to Fig. 1(b), two samples with the same spacer thickness of 70 
ML, we are able to rebuild the QD clusters by reducing the 
accumulated strain. The surface is characterized by steps plus 
terraces again and QD clusters decorate the ragged steps. 
Remarkably, the QDs in clusters are aligned as short chains. 
The visual appearance of the resulted surface morphology 
resembles itself as a jungle of bamboo. The bunched steps along 
[-113] visualize the individual bamboo sticks and aligned QD 
clusters separate each stick into sections. Very interesting, the 
QD clusters are nearly equally distributed along [-113]. Its 
periodicity is better resolved in the two-dimensional image of 
the autocorrelation functions calculated from the AFM image 
[14]. Figure 3(c) shows a line profile along [-113] through the 
center of Fig. 3(b). The separation between satellite peaks 
reveals that the periodicity is about 565 nm. The separations 
between “bamboos” are not uniform but still resolved from Fig. 
3(b), around 1.08 m. 
In conclusion, we stacked multilayer of InGaAs 
nanostructures on GaAs(731), and studied the effect by varying 
GaAs spacer thickness and InGaAs coverage. The resulted 
surface morphologies and optical properties are sensitive to the 
accumulated strain. GaAs(731) is demonstrated as a good 
candidate for growing QD clusters. The possibility of QD 
ordering inside clusters is revealed by AFM for low coverage of 
InGaAs. Our report indicates the need to study InGaAs growth 
on GaAs surfaces lying inside the stereographic triangle, thus 
achieve a comprehensive picture of strain-driven growth and 
pursuing novel QD configurations.  
 
Received 16 August 2009; accepted 31 August 2009; published 
online 15 October 2009. 
References 
1. S. Sanguinetti, S. Castiglioni, E. Grilli, M. Guzzi, G. 
Panzarini, L. C. Andreani and M. Henini, Jpn. J. Appl. 
Phys. 38, 4676 (1999). doi:10.1143/JJAP.38.4676 
2. H. Wen, Z. M. Wang and G. J. Salamo, Appl. Phys. Lett. 84, 
1756 (2004). doi:10.1063/1.1664018 
3. Y. Temko, T. Suzuki, M. C. Xu and K. Jacobi, Surf. Sci. 
591, 117 (2005). doi:10.1016/j.susc.2005.06.026 
4. Y. Temko, T. Suzuki, M. C. Xu, K. potschke, D. Bimberg 
and K. Jacobi, Phys. Rev. B 71, 045336 (2005). FIG. 3. (a) 5×5 μm AFM image of InGaAs/GaAs(731) multilayers with InGaAs
coverage of 5.7 ML and GaAs spacer of 70 ML. (b) Two-dimensional image of
autocorrelation functions calculated from (a). (c) A line profile along [-113] 
crossing the center of (b). The scale bar of 500 nm and the lateral direction of
[-113] apply to both (a) and (b). 
5. M. Zervos, C. Xenogianni, G. Deligeorgis, M. 
Androulidaki, P. G. Savvidis, Z. Hatzopoulos and N. T. 
Pelekanos, Phys. Status Solidi C 3, 3988 (2006). 
6. B. L. Liang, Zh. M. Wang, Yu. I. Mazur, Sh. 
Seydmohamadi, M. E. Ware and G. J. Salamo, Optics 
Express 15, 8157 (2007). doi:10.1364/OE.15.008157 
7. C. Wang, Y. Yang, X.M. Chen, Z.L. Liu, H.Y. Cui, S. 
Zhang, X.S. Chen and W. Lu, Appl. Surf. Sci. 254, 4626 
(2008). doi:10.1016/j.apsusc.2008.01.089 
8. Zh. M. Wang, C. Rodriguez, Sh. Seydmohamadi, Yu. I. 
Mazur, Y. Z. Xie and G. J. Salamo, Appl. Phys. Lett. 94, 
083107 (2009). doi:10.1063/1.3089695 
9. J. Marquez, L. Geelhaar and K. Jacobi, Appl. Phys. Lett. 
78, 2309 (2001). doi:10.1063/1.1365101 
10. D. Leonard, M. Krishnamurthy, C. M. Reaves, S. P. 
Denbaars and P. M. Petroff, Appl. Phys. Lett. 63, 3203 
(1993). doi:10.1063/1.110199 
11. D. Bimberg, M. Grundmann and N. N. Ledentsov, 
Quantum Dot Heterostructures (Wiley, Chichester, 1999). 
12. S. S. Li, J. B. Xia, J. L. Liu, F. H. Yang, Z. C. Niu, S.L. 
Feng and H.Z. Zheng, J. Appl. Phys. 90, 6151 (2001). 
doi:10.1063/1.1416855 
13. L. Geelhaar, J. Marquez, P. Kratzer and K. Jacobi, Phys. 
Rev. Lett. 86, 3815 (2001). doi:10.1103/PhysRevLett.86. 
3815 
14. Z. M. Wang, J. L. Shultz and G. J. Salamo, Appl. Phys. Lett. 
83, 1749 (2003). doi:10.1063/1.1606891 
 


file:///data/core-remote/dit/data/Springer-OA/pdf/c38/aHR0cDovL2xpbmsuc3ByaW5nZXIuY29tLzEwLjEwMDcvQkYwMzM1MzU5Ni5wZGY=.pdf

Multiple stacking of InGaAs/GaAs (731) nanostructures

Abstract

Similar works

Full text

Available Versions

Springer - Publisher Connector

Springer - Publisher Connector