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Device structure and characterization. (a) Schematic cross section of the device indicating the accumulation of a 2DEG at the interface and the local depletion by the barrier gates. (b) Scanning electron microscopy top-view of the device before the top gate is deposited. (c) Turn-on characteristics of the device at 300 K and 290 mK when a positive voltage is applied to all the three surface gates. . (d) Data from a different device at 4.2 K. Drain barrier gate presents an electrical discontinuity. Dual-side gating (DB1 and DB2 simultaneously biased) allows flexible control of the tunnel barrier.
SET characterization at 290 mK. (a) Device conductance as a function of the barrier gate voltages for and . (b) Coulomb blockade diamonds as a function of for and . Differential conductance measured using a lock-in excitation voltage of .
Device tunability. (a) Stability diagram for a large range of top gate voltages showing periodic regular Coulomb diamonds. Lock-in AC excitation of . and . (b) Total capacitance of the SET island as a function of . Periodic CB oscillations for different barrier gates biasing conditions for : (c) , (d) , (e) .
Dopant signatures. (a) Source barrier voltage differential conductance at low . Two clear transition a, b are observable in the subthreshold regime as well as irregular resonances c at larger . (b) Source barrier stability diagram acquired with a lock-in AC excitation voltage of . The charging energy of the system is 20 meV.
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