Dynamic Aspects of Droplet Epitaxy Studied by Low Energy Electron Microscopy

Droplets on semiconductor surfaces are receiving considerable attention because of their important role in fabricating nanostructures. For example, liquid Ga (or other group III metal) droplets on GaAs can transform into intricate quantum structures when placed under arsenic flux (As2 or As4) [1]. These range from dots to quantum rings, double rings, multi-rings, molecules and wires. This so-called droplet epitaxy method of nanostructure fabrication offers some unique features compared with conventional Stranski-Krastanow methods of quantum structure formation [2] including the separate control of size and shape, growth on unconventional surfaces and the fabrication of strain-free structures.
Liquid droplets are the basis of droplet epitaxy and it is advantageous to study and understand their behavior in real-time, at elevated temperature and, where necessary, under As flux. With this in mind we have combined a small III-V MBE system with a surface electron microscope to create a III-V low energy electron microscope (LEEM) system [3]. We have applied this technique to study a number of phenomena related to droplet behavior on surfaces including an intrinsic mechanism for motion during Langmuir evaporation [4], daughter droplet formation during coalescence [5], nanostructure writing utilizing a morphology dependent congruent evaporation temperature [5] and quantum ring and disk formation during droplet epitaxy [6]. Additionally, we will report on very recent work relating to surface reconstruction changes in the vicinity of droplets and the development of new characterization techniques including convergent beam low energy electron diffraction and Lloyd’s mirror photoemission electron microscopy [7].

[1] See, for example, C. Somaschini, S. Bietti, N. Koguchi, and S. Sanguinetti, Appl. Phys. Lett. 97, 203109 (2010).
[2] See, for example, D. Bimberg, M. Grundmann, and N. N. Ledentsov, Quantum Dot Heterostructures (Wiley, New York, 1998).
[3] D. E. Jesson and W. X. Tang, in Microscopy: Science, Technology, Applications and Education, edited by A. Méndez-Vilas and J. D. Álvarez (Formatex Research Center, Badajoz, Spain, 2010) Chap. 3, pp. 1608-1619.
[4] J. Tersoff, D. E. Jesson, and W. X. Tang, Science 324, 236 (2009).
[5] J. Tersoff, D. E. Jesson, and W. X. Tang, Phys. Rev. Lett. 105, 036102 (2010).
[6] Z. Y. Zhou, C. X. Zheng, W. X. Tang, J. Tersoff and D. E. Jesson, Phys. Rev. Lett. 111, 035702 (2013).
[7] D. E. Jesson, K. M. Pavlov, M. J. Morgan and B. F. Usher, Phys. Rev. Lett. 99 016103 (2007).

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