Morphology and growth of capped Ge/Si quantum dots

  • Yizhak Yacoby
  • Naomi Elfassy
  • Samit K. Ray
  • Raj K. Singha
  • Samaresh Das
  • Eyal Cohen
  • Shira Yochelis
  • Roy Clarke
  • Yossi Paltiel
Research Paper
Part of the following topical collections:
  1. Nanostructured Materials 2012. Special Issue Editors: Juan Manuel Rojo, Vasileios Koutsos

Abstract

The morphology, atomic structure, and chemical composition of small (4 nm average height and 20 nm average diameter), dense capped MBE-grown Ge/Si quantum dots are studied using an energy-differential extension of the direct X-ray phasing method, COBRA. Our results lead to the following conclusions: (i) the quantum dot system has a partial wetting layer; (ii) in the lower parts of the dots, the Ge content is small and increases toward the top; and (iii) the contact angle between the dots and the substrate is acute, consistent with the presence of a wetting layer. A growth mechanism compatible with these findings is proposed.

Keywords

Nano-crystals Quantum dots X-ray crystallography Self-assembly MBE 

References

  1. Abstreiter G, Schittenhelm P, Engel C, Silveira E, Zrenner A, Meertens D, Jager W (1996) Growth and characterization of self-assembled Ge-rich islands on Si. Semicond Sci Technol 11:1521–1528CrossRefGoogle Scholar
  2. Alguno A, Usami N, Ujihara T, Fujiwara K, Sazaki G, Nakajima K, Shiraki Y (2003) Enhanced quantum efficiency of solar cells with self-assembled Ge dots stacked in multilayer structure. Appl Phys Lett 83:1258CrossRefGoogle Scholar
  3. Aroutiounian V, Petrosyan S, Khachatryan A, Touryan K (2001) Quantum dot solar cells. J Appl Phys 89:2268CrossRefGoogle Scholar
  4. Baribeau JM, Wu X, Lockwood DJ (2006a) Probing the composition of Ge dots and Si/Si1−xGex island superlattices. J Vac Sci Technol A 24:663CrossRefGoogle Scholar
  5. Baribeau JM, Wu X, Rowell NL, Lockwood DJ (2006b) Ge dots and nanostructures grown epitaxially on Si. J Phys Condens Matter 18:R139CrossRefGoogle Scholar
  6. Baskaran A, Smereka P (2012) Mechanisms of Stranski–Krastanow growth. J Appl Phys 111:044321CrossRefGoogle Scholar
  7. Biasiol G, Heun S (2011) Compositional mapping of semiconductor quantum dots and rings. Phys Rep 500:117–173CrossRefGoogle Scholar
  8. Capellini G, Motta N, Sgarlata A, Calarco R (1999) Evolution of strained Ge islands grown on Si(111): a scanning probe microscopy study. Solid State Commun 112:145–149CrossRefGoogle Scholar
  9. Caroff P, Bertru N, Platz C, Dehaese O, Le Corre A, Loualiche S (2005) Emission wavelength control of InAs dots quantum dots in a GaInP matrix grown on InP (311)B substrates. J Cryst Growth 273:357–362CrossRefGoogle Scholar
  10. Chaparro SA, Zhang Y, Drucker J, Chandrasekhar D, Smith DJ (2000) Evolution of Ge/Si(100) islands: island size and temperature dependence. J Appl Phys 87:2245CrossRefGoogle Scholar
  11. Cohen E, Yochelis S, Westreich O, Shusterman S, Kumah DP, Clarke R, Yacoby Y, Paltiel Y (2011) Structure of droplet-epitaxy-grown InAs/GaAs quantum dots. Appl Phys Lett 98:243115CrossRefGoogle Scholar
  12. Denker U, Stoffel M, Schmidt OG (2003) Probing the lateral composition profile of self-assembled islands. Phys Rev Lett 90:196102CrossRefGoogle Scholar
  13. Drucker J (2002) Self-assembling Ge (Si)/Si (100) quantum dots. IEEE J Quantum Electron 38:975CrossRefGoogle Scholar
  14. Floyd M, Zhang Y, Driver KP, Drucker J, Crozier PA, Smith DJ (2003) Nanometer-scale composition measurements of Ge/Si (100) islands. Appl Phys Lett 82:1473CrossRefGoogle Scholar
  15. Fong DD, Cionca C, Yacoby Y, Stephenson GB, Eastman JA, Fouss PH, Streiffer SK, Thompson C, Clarke R, Pindak R, Stern EA (2005) Direct structural determination in ultrathin ferroelectric films by analysis of synchrotron X-ray scattering measurements. Phys Rev B 71:144112CrossRefGoogle Scholar
  16. Grätzel M (2001) Photoelectrochemical cells. Nature 414:338CrossRefGoogle Scholar
  17. Hesse A, Stangl J, Holy V, Roch T, Bauer G, Schmidt OG, Denker U, Struth B (2002) Effect of overgrowth on shape, composition, and strain of SiGe islands on Si(001). Phys Rev B 66:085321CrossRefGoogle Scholar
  18. Kumah DP, Shusterman S, Paltiel Y, Yacoby Y, Clarke R (2009) Atomic-scale mapping of quantum dots formed by droplet epitaxy. Nat Nanotechnol 4:835CrossRefGoogle Scholar
  19. Kumah DP, Wu JH, Husseini NS, Dasika VD, Goldman RS, Yacoby Y, Clarke R (2011) Correlating structure, strain, and morphology of self-assembled InAs quantum dots on GaAs. Appl Phys Lett 98:021903CrossRefGoogle Scholar
  20. Lang C (2003) Composition of self-assembled quantum dots. Mater Sci Technol 19:411CrossRefGoogle Scholar
  21. Ledentsov NN, Ustinov VM, Shchukin VA, Kop’ev PS, Alferov ZI, Bimberg D (1998) Quantum dot heterostructures: fabrication, properties, lasers. Semiconductors 32:343CrossRefGoogle Scholar
  22. Liao XZ, Zou J, Cockayne DJH, Wan J, Jiang ZM, Jin G, Wang KL (2002) Alloying, elemental enrichment, and interdiffusion during the growth of GeSi 001 quantum dots. Phys Rev B 65:153306CrossRefGoogle Scholar
  23. Magidson V, Regelman DV, Beserman R, Dettmer K (1998) Evidence of Si presence in self-assembled Ge islands deposited on a Si, 001 substrate. Appl Phys Lett 73:1044–1046CrossRefGoogle Scholar
  24. Rastelli A, Stoffel M, Malachias A, Merdzhanova T, Katsaros G, Kern K, Metzger TH, Schmidt OG (2008) Three-dimensional composition profiles of single quantum dots determined by scanning-probe-microscopy-based nanotomography. Nano Lett 8:1404–1409CrossRefGoogle Scholar
  25. Robel I, Subramanian V, Kuno M, Kamat PV (2006) Quantum dot solar cells: harvesting light energy with CdSe nanocrystals moleculary linked to mesoscopic TiO2 films. J Am Chem Soc 128:2385CrossRefGoogle Scholar
  26. Schülli TU, Stangl J, Zhong Z, Lechner RT, Sztucki M, Metzger TH, Bauer G (2003) Direct determination of strain and composition profiles in Si Ge islands by anomalous X-ray diffraction at high momentum transfer. Phys Rev Lett 90:066105CrossRefGoogle Scholar
  27. Singha RK, Das S, Majumdar S, Das K, Dhar A, Ray SK (2008) Evolution of strain and composition of Ge islands on Si (001) grown by molecular beam epitaxy during post-growth annealing. J Appl Phys 103:114301CrossRefGoogle Scholar
  28. Singha RK, Manna S, Das S, Dhar A, Ray SK (2010) Room temperature infrared photoresponse of self assembled Ge/Si (001) quantum dots grown by molecular beam epitaxy. Appl Phys Lett 96:233113CrossRefGoogle Scholar
  29. Sowwan M, Yacoby Y, Pitney J, MacHarrie R, Hong M, Cross J, Walko DA, Clarke R, Pindak R, Stern EA (2002) Direct atomic structure determination of epitaxially grown films: Gd2O3 on GaAs(100). Phys Rev B 66:205311CrossRefGoogle Scholar
  30. Stangl J, Holý V, Bauer G (2004) Structural properties of self-organized semiconductor nanostructures. Rev Mod Phys 76:725CrossRefGoogle Scholar
  31. Wang KL, Cha D, Liu J, Chen C (2007) Ge/Si self-assembled quantum dots and their optoelectronic device applications. Proc IEEE 95:1866CrossRefGoogle Scholar
  32. Yacoby Y, Pindak R, MacHarrie R, Pfeiffer L, Berman L, Clarke R (2000) Direct structure determination of systems with two-dimensional periodicity. J Phys Condens Matter 12:3929–3938CrossRefGoogle Scholar
  33. Yoffe D (2001) Semiconductor quantum dots and related systems: electronic, optical, luminescence and related properties of low dimensional systems. Adv Phys 50:1CrossRefGoogle Scholar
  34. Zhang Y, Drucker J (2003) Annealing-induced Ge/Si (100) island evolution. J Appl Phys 93:15Google Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  • Yizhak Yacoby
    • 1
  • Naomi Elfassy
    • 2
  • Samit K. Ray
    • 3
  • Raj K. Singha
    • 3
  • Samaresh Das
    • 3
  • Eyal Cohen
    • 2
  • Shira Yochelis
    • 2
  • Roy Clarke
    • 4
  • Yossi Paltiel
    • 2
  1. 1.Racah Institute of PhysicsHebrew UniversityJerusalemIsrael
  2. 2.Department of Applied PhysicsHebrew UniversityJerusalemIsrael
  3. 3.Department of Physics and MeteorologyIndian Institute of Technology KharagpurKharagpurIndia
  4. 4.Applied Physics Program, and Center for Solar and Thermal Energy ConversionUniversity of MichiganAnn ArborUSA

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