Direct-write single electron transistors by focused electron beam induced deposition

Single-electron transistor (SET) device fabrication for operation in the tens of Kelvin range is still challenging due to the need of controlled definition of the metallic island with a diameter far below 100 nm and proper tuning of the island's tunnel couplings to the drain and source leads. Here we present results on SET device fabrication using focused electron beam induced deposition (FEBID) for island definition between pre-fabricated SET electrode structures. The island's nano-granular microstructure allows us, in conjunction with in situ tuning of the inter-grain tunnel coupling by post-growth electron irradiation, to study the effect of the island's electronic granularity on SET device performance. In addition we show that for reliable SET operation FEBID-associated co-deposit in proximity of the island has to be removed which can be accomplished by a novel in situ Ar ion etching process. For the low-temperature properties of functioning SET devices we obtain good agreement of capacitance values deduced from the current-voltage characteristics and capacitance calculations based on the geometry of the device electrodes and the microstructure of the island. Complementary simulations of the SET current-voltage characteristics based on the master equation approach are in good agreement with the experimental data. The observation of well-defined Coulomb oscillations indicates that FEBID-based SET structures can be useful as on-demand charge monitor devices with high lateral positioning flexibility.