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(a) SEM image of the Si MOS DQD. The three BGs and the TG have widths and , respectively. The Al BGs were plasma-oxidized to isolate them from the TG. (b) Schematic cross section of the device. Source and drain contacts (red) were formed by phosphorus diffusion into the Si substrate (light blue). The TG induces a 2DEG and the BGs create three potential barriers, forming two dots. The size of the dots is estimated to be . (c) Color-enhanced XTEM image of a similar device. (d) Enlarged XTEM image, showing sharp interfaces between the Si substrate, gate oxide, and the Al TG.
Differential conductance =0 V as a function of and , for and =0 V. Tuning the middle BG voltage in the range , we observe a transition from two almost isolated dots (a) to the formation of a single large dot (b).
Bias spectroscopy of a weakly coupled DQD with . (a) At finite , the triple points develop into triangle pairs. [(b) and (c)] Detailed bias spectroscopy of a pair of triangles at and 0.5 mV. (d) Line cut along the red arrow in (b) shows resonant tunneling through excited states in the transport.
Comparison of experimental values obtained from Fig. 3(a) and modeled FASTCAP capacitances. For definitions, see text.
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