Heiss W.D. (ed.) Quantum dots.. a doorway to - tiera.ru

50 J.M. Elzerman et al.
a b
c
200 nm
500 nm
200 nm
Fig. 14. Few-electron quantum dot devices. (a) Scanning electron microscope image
of the first sample, showing the metal gate electrodes (light) on top of a
GaAs/AlGaAs heterostructure (dark) that contains a 2DEG 90 nm below the surface
(with electron density 2.9 × 10 11 cm −2 ). This device was used only as a few-electron
single dot. Due to the similarity of the image to characters from the Japanese “Gundam”
animation, this has become known as the Gundam design. The two gates
coming from the top and ending in small circles (the “eyes”) were meant to make
the dot confinement potential steeper, by applying a positive voltage to them (up
to ∼0.5 V). The gates were not very effective, and were left out in later designs.
(The device was fabricated by Wilfred van der Wiel at NTT Basic Research Laboratories.)
(b) Scanning electron microscope image of the second device, made on
a similar heterostructure. It was used only as a few-electron single dot, and was
more easily tunable than the first one. (The device was fabricated by Wilfred van
der Wiel and Ronald Hanson at NTT Basic Research Laboratories.) (c) Atomic
force microscope image of the third device, made on a similar heterostructure. This
design, with two extra side gates to form two quantum point contacts, was operated
many times as a single dot, and twice as a few-electron double dot. It was used for
all subsequent measurements. A zoom-in of the gate structure is shown in Fig. 16a.
(The device was fabricated by Ronald Hanson and Laurens Willems van Beveren at
NTT Basic Research Laboratories)