Epitaxially Self-Assembled Quantum Dots

Petroff, P.M., Lorke, A., Imamoglu, A., 2001. Epitaxially self-assembled quantum dots. Phys. Today 54, 46—52. 

Petroff P, Lorke A, Imamoglu A (2001) Epitaxially Self-Assembled Quantum Dots. Phys Today 54 46-51... 

The method of templated self assembly has been recently successfully implemented for the growth of ordered arrays of InAs as well as Ge islands in 2-and 3-dimensional arrays and quantum dot crystals [1] by molecular beam epitaxy (MBE). The quantum dot arrays fabricated by templated self-assembly exhibit narrow size distributions and perfect ordering [2]. Thus, this technology enables fabrication of nanodevices requiring exact positioning of quantum dots [3] and offers a suitable path for the demonstration of spintronics and manipulation of qubits [4]. 

Quantum dots are the engineered counterparts to inorganic materials such as groups IV, III-V and II-VI semiconductors. These structures are prepared by complex techniques such as molecular beam epitaxy (MBE), lithography or self-assembly, much more complex than the conventional chemical synthesis. Quantum dots are usually termed artificial atoms (OD) with dimensions larger than 20-30 nm, limited by the preparation techniques. Quantum confinement, single electron transport. Coulomb blockade and related quantum effects are revealed with these OD structures (Smith, 1996). 2D arrays of such OD artificial atoms can be achieved leading to artificial periodic structures. 

Z. Z. Sun, S. F. Yoon, K. C. Yew, W. K. Loke, S. Z. Wang, and T. K. Ng, Self-assembled GalnNAs/GaAs quantum dots grown by solid-source molecular beam epitaxy, J. Crystal Growth 242, 109-115 (2002). 

Mitsuru Sugawara, Theoretical Bases of the Optical Properties of Semiconductor Quantum Nano-Structures Yoshiaki Nakata, Yoshihiro Sugiyama, and Mitsuru Sugawara, Molecular Beam Epitaxial Growth of Self-Assembled InAs/GaAs Quantum Dots... 

Abstract Some aspects of self-assembly of quantum dots in thin solid films are considered. Nonlinear evolution equations describing the dynamics of the fihn instability that results in various surface nanostructures are analyzed. Two instability mechanisms are considered the one associated with the epitaxial stress and the other caused by the surface-energy anisotropy. It is shown that wetting interactions between the film and the substrate transform the instability spectrum from the long- to the short-wave type, thus yielding the possibility of the formation of spatiaUy-regular, stable arrays of quantum dots that do not coarsen in time. Pattern formation is analyzed by means of ampbtude equations near the insta-bibty threshold and by numerical solution of the strongly nonlinear evolution equations in the small-slope approximation. 

We have discussed certain aspects of self-assembly of quantum dots from thin solid films epitaxially grown on solid substrates. We have considered two principle mechanisms of instability of a planar film that lead to the formation of quantum dots the one associated with epitaxial stress and the one associated with the anisotropy of the film surface energy. We have focused on the case of particularly thin hlms when wethng interactions between the film and the substrate are important and derived nonlinear evolution equations for the him surface shape in the small-slope approximahon. We have shown that wetting interachons between the him and the substrate damp long-wave modes of instability and yield the short-wave instability spectrum that can result in the formahon of spahally-regular arrays of islands. We have discussed the nonlinear evoluhon of such arrays analyhcally, by means of weakly nonlinear analysis, and numerically, far from the instability threshold and have shown... 

The concept of templated self-assembly of quantum dots has been transferred from molecular beam epitaxy to chemical vapour deposition. Here we demonstrate the fabrication of ordered arrays of Ge islands on a Si (100) surface using optical holography for the prepattern and subsequent growth by chemical vapor deposition. The samples were analyzed by atomic force microscopy and photoluminescence. Ordered arrays of Ge islands with a narrow size distribution and intense narrow photoluminescence lines of the islands have been observed. 

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