In situ accurate control of 2D3D transition parameters for growth of lowdensity InAs/GaAs selfassembled quantum dots
 MiFeng Li^{1}Email author,
 Ying Yu^{1},
 JiFang He^{1},
 LiJuan Wang^{1},
 Yan Zhu^{1},
 Xiangjun Shang^{1},
 HaiQiao Ni^{1} and
 ZhiChuan Niu^{1}Email author
DOI: 10.1186/1556276X886
© Li et al.; licensee Springer. 2013
Received: 26 December 2012
Accepted: 6 February 2013
Published: 18 February 2013
Abstract
A method to improve the growth repeatability of lowdensity InAs/GaAs selfassembled quantum dots by molecular beam epitaxy is reported. A sacrificed InAs layer was deposited firstly to determine in situ the accurate parameters of two to threedimensional transitions by observation of reflection highenergy electron diffraction patterns, and then the InAs layer annealed immediately before the growth of the lowdensity InAs quantum dots (QDs). It is confirmed by microphotoluminescence that control repeatability of lowdensity QD growth is improved averagely to about 80% which is much higher than that of the QD samples without using a sacrificed InAs layer.
Keywords
InAs quantum dots Sacrificed InAs layer Molecular beam epitaxy Reflection highenergy electron diffraction Microphotoluminescence Low density 78.67.Hc 78.55.Cr 78.55.mBackground
Single selfassembled semiconductor quantum dots (QDs) are of increasing interest due to their applications in lowthreshold lasers[1], singlephoton and entangled photon sources[2, 3], quantum computing, and quantum information processing[4, 5]. Several techniques have been developed to obtain lowdensity QD structures, such as the StranskiKrastanov selfassembled growth of QDs on a substrate patterned with mesa/holes[6, 7], stopping of the rotation of the substrate to obtain a gradient density of InAs QDs[8, 9], and a modified droplet epitaxy method to lower the QDs' density[10]; especially one of the most effective method is to stop the InAs deposition at the onset of a twodimensional to threedimensional (2D3D) growth transition[11] by controlling the parameters of 2D3D growth transition such as temperature, growth rate, deposition amount of indium, and interruption time. However, the narrow range of deposition in the 2D3D growth transition determines that allowed deviations of controllable parameters are quite limited for repeatable growth of lowdensity QDs.
In this paper, to increase the repeatability and to obtain good singlephoton characteristics, we investigated a growth technique to obtain in situ the critical deposition in 2D3D growth transition and slightly change the critical conditions to achieve InAs QDs with good singlephoton characteristics. The success ratio is improved averagely to about 80% which is much higher than that of the traditional QD samples (less than 47%).
Methods
Growth parameters of sample 1 to sample 9
Samples  Growth temperature of SQD/QD (°C)  Growth rate (ML/s)  Deposition θ_{c} + Δ (ML)  Interruption time (s)  Annealing temperature (°C) 

1  520/525  0.005  θ_{c} + 0.15  10  610 
2  520/525  0.005  θ_{c} + 0.075  10  610 
3  520/525  0.005  θ_{c} + 0.025  10  610 
4  520/525  0.005  θ_{c} + 0  10  610 
5  520/525  0.005  θ_{c} − 0.05  10  610 
6  520/525  0.005  θ_{c} − 0.075  10  610 
7  520/525  0.005  θ_{c} + 0  10  580 
8  520/525  0.005  θ_{c} + 0  10  590 
9  /525  0.005  θ _{c}  10   
Results and discussion
By growing a reference sample to obtain the critical growth parameters, then increasing growth interruption and growth temperature, and decreasing deposition of InAs, a very low density of QDs can be realized[11]. However, the repeatability is very low if the critical conditions were obtained from samples in different batches because of the accidental error and system error, such as differences caused by different molybdenum sample holder blocks, ambience in the growth chamber, measurement of growth rate and temperature, and so on. For our samples used in this method, the repeatability is less than 47%.
Another reason for the low repeatability is that the condition of the lowdensity InAs QD for singlephoton source devices is strict, so a small deviation of deposition may affect the microPL seriously. The microPL spectra of samples 3 and 4 at 80 K are shown in Figure 4c,d. The sharp single peak indicates that sample 4 has a good singlephoton characteristic. The multiple peaks of sample 3 demonstrate that a slight change (0.025 ML) of deposition may determine the optical characteristic, so the critical growth parameters obtained from the reference sample ex situ make the repeatability low.
Conclusion
It is an important issue to accurately control the 2D3D transition parameters for the growth of lowdensity selfassembled InAs QDs. We have proposed a method of introducing a sacrificial InAs layer to determine in situ the 2D3D critical condition as a spotty pattern appears in RHEED. After annealing of the InAs sacrificial layer at 610°C, the expected lowdensity QDs can be grown with highly improved repeatability. As confirmed by microPL spectroscopy, high opticalquality lowdensity QDs were obtained under the growth temperature of 5°C higher than that of the SQD layer and the same deposition of InAs. The slight increase of the InAs deposition amount dramatically deteriorates the PL properties. Our result provides a useful way to accurately control the critical condition of the lowdensity InAs QDs and thus to improve the fabrication repeatability.
Authors' information
MFL, YY, JFH, LJW, YZ, and XjS are Ph.D. students at the Institute of Semiconductors, Chinese Academy of Sciences. HQN is associate researcher, and ZCN is a researcher at the State Key Laboratory for Superlattices and Microstructures, Institute of Semiconductors, Chinese Academy of Sciences.
Abbreviations
 θc:

Critical coverage
 PL:

Photoluminescence
 QD:

Quantum dot
 RHEED:

Reflection highenergy electron diffraction
 SQDs:

Sacrificed InAs quantum dots
 TEM:

Transmission electron microscopy.
Declarations
Acknowledgments
This work is supported by the National Natural Science Foundation of China (under grant nos. 90921015, 61176012, 61274125), the National Key Basic Research Program of China (grant nos. 2013CB933304, 2010CB327601, 2012CB932701), and the Strategic Priority Research Program (B) of the Chinese Academy of Sciences (grant no. XDB01010200).
Authors’ Affiliations
References
 Pelton M, Yamamoto Y: Ultralow threshold laser using a single quantum dot and a microsphere cavity. Phys Rev A 1999, 59: 2418–2421. 10.1103/PhysRevA.59.2418View ArticleGoogle Scholar
 Karrai K, Warburton RJ, Schulhauser C, Hogele A, Urbaszek B, McGhee EJ, Govorov AO, Garcia JM, Gerardot BD, Petroff PM: Hybridization of electronic states in quantum dots through photon emission. Nature 2004, 427: 135–138. 10.1038/nature02109View ArticleGoogle Scholar
 Thompson RM, Stevenson RM, Shields AJ, Farrer I, Lobo CJ, Ritchie DA, Leadbeater ML, Pepper M: Singlephoton emission from exciton complexes in individual quantum dots. Phys Rev B 2001, 64: 201302.View ArticleGoogle Scholar
 Bennett CH: Quantum cryptography using any two nonorthogonal states. Phys Rev Lett 1992, 68: 3121–3124. 10.1103/PhysRevLett.68.3121View ArticleGoogle Scholar
 Knill E, Laflamme R, Milburn GJ: A scheme for efficient quantum computation with linear optics. Nature 2001, 409: 46–52. 10.1038/35051009View ArticleGoogle Scholar
 Ishikawa T, Nishimura T, Kohmoto S, Asakawa K: Sitecontrolled InAs single quantumdot structures on GaAs surfaces patterned by in situ electronbeam lithography. Appl Phys Lett 2000, 76: 167–169. 10.1063/1.125691View ArticleGoogle Scholar
 Vitzethum M, Schmidt R, Kiesel P, Schafmeister P, Reuter D, Wieck AD, Dohler GH: Quantum dot microLEDs for the study of fewdot electroluminescence, fabricated by focused ion beam. Physica E 2002, 13: 143–146. 10.1016/S13869477(01)005069View ArticleGoogle Scholar
 Moskalenko ES, Karlsson FK, Donchev VT, Holtz PO, Monemar B, Schoenfeld WV, Petroff PM: Effects of separate carrier generation on the emission properties of InAs/GaAs quantum dots. Nano Lett 2005, 5: 2117–2122. 10.1021/nl050926aView ArticleGoogle Scholar
 Jin P, Ye XL, Wang ZG: Growth of lowdensity InAs/GaAs quantum dots on a substrate with an intentional temperature gradient by molecular beam epitaxy. Nanotechnology 2005, 16: 2775–2778. 10.1088/09574484/16/12/005View ArticleGoogle Scholar
 Liang BL, Wang ZM, Lee JH, Sablon K, Mazur YI, Salamo GJ: Low density InAs quantum dots grown on GaAs nanoholes. Appl Phys Lett 2006, 89: 043113. 10.1063/1.2244043View ArticleGoogle Scholar
 Sun J, Jin P, Wang ZG: Extremely low density InAs quantum dots realized in situ on (100) GaAs. Nanotechnology 2004, 15: 1763–1766. 10.1088/09574484/15/12/012View ArticleGoogle Scholar
 Patella F, Arciprete F, Fanfoni M, Balzarotti A, Placidi E: Apparent critical thickness versus temperature for InAs quantum dot growth on GaAs (001). Appl Phys Lett 2006, 88: 161903. 10.1063/1.2189915View ArticleGoogle Scholar
 Zhang BY, Solomon GS, Pelton M, Plant J, Santori C, Vuckovic J, Yamamoto Y: Fabrication of InAs quantum dots in AlAs/GaAs DBR pillar microcavities for single photon sources. J Appl Phys 2005, 97: 073507. 10.1063/1.1882764View ArticleGoogle Scholar
 Goldstein L, Glas F, Marzin JY, Charasse MN, Leroux G: Growth by molecular beam epitaxy and characterization of InAs/GaAs strainedlayer superlattices. Appl Phys Lett 1985, 47: 1099–1101. 10.1063/1.96342View ArticleGoogle Scholar
Copyright
This article is published under license to BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.