Quantum dots electron beam lithography

Figure 1. Selective growth of semiconductor quantum dots (Ge or Si) in Si windows in an SiO2 layer. In large area Si windows ((bi), (b2), d > 270 nm), few dots per window are grown [4]. In small area windows ((ci), (c2), d < 270 nm) only one dot per window is grown [4], For samples (bi), (b2) the windows in SiO2 were defined by electron beam lithography [4], while for samples (ci), (c2) by focussed ion beam milling [6],...

For the fabrication of quantum wires, the above-mentioned quantum wells are used as precursor. The wells are then patterned by electron beam lithography and dry- or wet-chemical etching [26,41-43]. This method is also used to fabricate quantum dots with regular spatial distribution. The resulting wires or dots have well-defined widths and lengths down to about 10 nm. A disadvantage of this method is the low density of quantum dots on the surface area and the fact that it is very difficult to obtain structures below certain sizes. A further method for the fabrication of quantum wires with high concentrations per volume unit is the electrochemical deposition of the semiconductor material into the cavities of anodic aluminum oxide. The aluminum oxide can be removed chemically and one obtains quantum wires with diameters down to 9 nm [44-46]. 

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. 

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